The Earth Through TimeCHAPTER 12—LIFE OF THE PALEOZOIC

CHAPTER OUTLINE FOR TEACHING

I. Overview of Life’s Expansion

A. Cambrian: vast expansion of shelly marine life forms; jawless fishes

B. Ordovician: most modern phyla established by this time

C. Late Paleozoic: land plants and vertebrates (tetrapods and amniotes) are very successful in populating the continents

D. Mass Extinctions: within Ordovician and Devonian; end of Permian

II. Invertebrates of the Paleozoic: arrival of animals with shells

A. Review of Significant Early Cambrian Fossils

1. Cloudina2. Anabarites3. Aldanella4. Lapworthella

B. Review of Significant Middle Cambrian Fossils

1. Aysheaia2. Leanchoila3. Waptia4. Anomalocaris5. Marrella6. Hallucigenia7. Opabinia8. Pikaia9. Cathaymyrus and Yunnanozoon

C. Extraordinary Cambrian Soft-Body Fossil Sites

1. Burgess Shale, British Columbia, Canada a. viewed as one of the most important faunas in fossil recordb. impressions and films on bedding planesc. limited exposure near Mt. Wapta, BCd. discovered by C.D. Walcott in 1909e. four groups of arthropods (trilobites, crustaceans, scorpions, insects)f. other groups: sponges, onycophorans, crinoids, sea cucumbers,

chordates, other unknown forms2. Chengjian site, Yunnan Province, China

a. about 10 million years older than Burgess Shaleb. discovered in 1984

c. early chordates and oldest fishes

D. The Cambrian explosion of life

1. Sudden increase in the pace of evolution2. Possible causes

a. more beneficial climatic conditions following glacial episodes and the related demise of the Ediacaran animals

b. changes in the sequences of HOX genes that control body architecturec. combination of factors, some of which may not be known

E. The Great Ordovician Biodiversification Event (GOBE)

1. Middle Ordovician, only 40 million years after the Cambrian explosion2. Tripling of global biodiversity in only 25 million years3. Accompanied fragmentation of continents and proliferation of shallow, warm

water habitats4. New groups

a. trilobitesb. brachipodsc. bivalve mollusksd. gastropodse. coralline animals

5. Newly diverse life strategiesa. epifaunal and infaunalb. filter and sediment feedingc. herbivores, carnivores, and scavengers

III. Invertebrates of the Paleozoic

A. Diversification of Many Groups

1. Epifaunal animals2. Infaunal animals (bioturbation)3. Filter-feeding animals4. Sediment-feeding animals

B. Unicellular Groups

1. Foraminifera (calcareous microfossils)a. range Cambrian to presentb. more numerous and varied by Carboniferousc. global distribution during Pennsylvanian-Permian (fusulinids)

2. Radiolarians (siliceous microfossils)a. range Early Paleozoic to presentb. most abundant in Mesozoic rocks

C. Marine Invertebrate Groups

1. Colonial cup animalsa. archaeocyathidsb. sponges (Porifera)

(i) well-known guide fossils Cambrian: Protospongia Silurian: Astraeospongium Devonian: Hydnoceras

(ii) sponge-like fossils: stromatoporoidsc. corals and other cnidarians

(i) rugose or tetracorals(ii) scleractinid or hexacorals(iii) tabulates

2. Bryozoans3. Brachiopods

a. articulateb. inarticulate

4. Mollusksa. placophoransb. monoplacophoransc. bivalvia or pelecypoda

(i) clams(ii) mussels(iii) scallops(iv) oysters

d. gastropodse. cephalopods

5. Arthropodsa. trilobitesb. ostracodsc. eurypterids

6. Echinodermsa. asteroidea (starfish)b. ophiuroidea (brittle stars)c. echinoidea (sea urchins)d. edioasteroidea (ancestral starfish and sea urchins)e. crinoidea (crinoids)f. cystoidea (cystoids)g. blastoidea (blastoids)h. rhombiferai. diploporita

7. Graptolites: primitive chordates called pterobranchs

IV. Vertebrates (Chordates) of the Paleozoic

A. Basic Groups

1. Non-Amniotic vertebratesa. fish and amphibiansb. require water to reproduce

2. Amniotic vertebratesa. all higher vertebratesb. have enclosed eggs

3. Chordatesa. stiff, elongate support structure with central nerve cordb. gill slits and ventral and dorsal blood circulation

B. Fishes: five taxonomic classes

1. Agnathids (jawless fish): ostracoderms2. Acanthodians and Placoderms (archaic jawed fish)

a. placodermsb. arthrodiresc. antiarchs

3. Chondrichthyans (cartilaginous fish)4. Osteichthyans (bony fish)

a. actinopterygians (ray-fined fish)b. sarcopterygians (lobe-finned fish)

(i) dipnoans (lungfish)(ii) crossopterygians (lobe-finned fish with limbs)

rhipidistians coelacanths

C. Conodont elements (microfossil teeth)

1. Range: Late Paleozoic-Triassic2. Fossil hard parts: tooth-like calcium phosphate fossils3. Whole body form: eel-like, 40 mm long, a primitive jawless vertebrate with

many teeth (Promissum)

D. Crossopterygians: transitional animals between fish and amphibians that had forelimbs1. Tiktaalik2. Eusthenopteron

E. Tetrapods

1. Amphibians (egg-laying tetrapods that reproduce in water)a. ichthyostegids: fish-like amphibians (basal tetrapods)b. labyrinthodonts: teeth similar to ray-fin fishes

2. Reptiles, Birds, and Mammals (Amniotic tetrapods)a. Late Carboniferous subdivision

(i) reptiles(ii) synapsids

b. Permian-Triassic groups(i) therapsids (mammal-like reptiles)(ii) cynodonts (an especially mammal-like group)

V. Plants of the Paleozoic

A. Stromatolites and stromatolitic reefs: Cambrian-Ordovician

B. Non-stromatolitic algae of Early Paleozoic

1. Chlorophytes2. Receptaculids (lime-secreting algae sometimes called “sunflower corals”)

C. Land plants

1. Bryophytes (mosses, liverworts, hornworts)2. Tracheophytes (ferns and trees)

a. lycopsids (scale trees)(i) Lepidodendron(ii) Sigillaria

b. cordaites

VI. Mass Extinctions

A. Late Ordovician: global cooling event due to Gondwanaland’s ice caps

1. Phase-one victims: planktonic and nektonic organisms (graptolites, acritarchs, and many nautloids) a. associated with global cooling, which shifted living groups toward the

equatorb. sea level was lowered and epeiric seas and shallow shelf areas lost due to

regression2. Phase-two victims: benthic organisms (surviving trilobites; great reduction in

numbers of corals, conodonts, bryozoans, and brachiopods)a. associated with global coolingb. sea level rising due to ice-sheet melting c. warmer conditions stressed cold-adapted groups

B. Late Devonian: global cooling due to Gondwanaland glaciation

1. Decimated Devonian reef communities including tabulate corals and stromatoporoids

2. Severely reduced: rugose corals, brachiopods, goniatites, trilobites, conodonts, and placoderms

3. Marine invertebrates in general: loss of 70% of families4. Occurred over 20 million years, therefore an ecological crisis of some kind

a. eutrophication or anoxic conditions in the oceansb. continental glaciation: cooling and regression of seas

C. Late Permian (“Mother of Mass Extinctions”)

1. Continental effectsa. 70% of land animal species exterminatedb. extinction of families of amphibians, primitive reptiles, mammal-like

reptiles2. Marine effects

a. most strongly affected the tropicsb. 90% of marine species exterminatedc. extinction of fusulinids, rugose corals, many crinoids, productid

brachiopods, lacy bryozoans, many ammonoid groups3. Factors

a. extreme global warmingb. greenhouse gas effectsc. massive flood basalt eruptionsd. carbon-dioxide poisoninge. ozone layer damage or loss

Answers to Discussion Questions

1. In the Burgess Shale, Pikaia is a chordate. In the Chengjian site, China, Cathysmyrus and Yunnanozoon are chordates. Chordates have a notochord (at some stage of development) and a related nerve cord on the dorsal side of the notochord. Fossils with evidence of these features are classified as chordates.

2. Here are the age assignments of the fossils indicated:

fusulinids Pennsylvanian-Permianarchaeocyathids Early-Middle CambrianArchimedes Mississippian

3. The presence of stinging cells, or cnidocytes, characterizes all members of the Phylum Cnidaria, and thus the phylum is so named. The extinct forms are tabulate and rugose corals.

4. Cephalopods of the Subclass Nautiloidea have straight or gently undulating sutures, whereas the Ammonoidea have more complex sutures.

5. Conodont elements consist of cones, bars, and blades bearing tiny denticles or cusps. These elements are made of calcium phosphate (a variety of the mineral apatite), a material common in teeth of vertebrates.

6. By the end of Paleozoic, many invertebrate groups had become extinct, including fusulinids, rugose corals, many families of crinoids, productid brachiopods, trilobites, lacy bryozoans, and many groups of ammonoids.

7. Shallow shelf and epeiric sea environments are affected by episodes of continental glaciation when sea level is lowered due to ice buildup at high latitude. Cooling of water also makes calcium carbonate precipitation move difficult, so the amount of carbonate deposition is greatly decreased.

8. Echinoderms are largely sessile spiny skinned animals which generally consist of a crown, stem, and arms. Trilobites are mobile, three-lobed arthropods which were highly successful Paleozoic animals, but are extinct today. Mollusks are a diverse group which all have in common a foot and a mantle (which secrets shell, if any). The Mollusks have various strategies of life: infaunal, epifaunal, and mobile. The Brachiopods are symmetrical bivalves that are filter feeders. The Brachiopods still exist but were at their peak of diversity during Paleozoic. The Bryozoa are colonial organisms consisting of collections of zooecia; they generally form branching or encrusting shapes. The Porifera (sponges) consist mainly of an osculum, choanocytes, mesenchyme, and flagellae. The Porifera are attached forms; their fossil record is mainly as spicules of silica or calcium carbonate.

9. Evolution of the shell provided obvious physical protection for the invertebrate. Further, the shell permitted more efficient locomotion in water and sediment.

10. (a) Ostracaderms and placoderms – The former are Early Paleozoic armored, jawless fishes (Agnatha), and the latter, armored jawed fishes.

(b) Osteichthyes and chondrichthyes – The former are bony fishes, and the latter, cartilaginous fishes (e.g., sharks).

(c) Sarcopterygians and labyrinthodonts – The former are lobe-finned fish, and the latter, a lung fish with specialized teeth made of infolded enamel. (d) Infaunal and epifaunal invertebrates – The former live within sediment or rock, and the latter, upon sediment or rock.

(e) Synapsids and diapsids – The former type of tetrapod has one temporal fenestra (opening) on each side of the skull, and the latter, two fenestra on each side.

11. Tiktaalik was a transitional animal between fish and amphibians that had forelimbs. These forelimbs had the beginnings of fingers, wrist bones, elbows, and shoulders. The upper arm (humurus) resembled both that of the fish and the amphibian.

12.Therapsid reptile characteristics indicating eventual mammalian evolution include: fewer bones in the skull, enlarged lower jaw at the expense of more posterior elements, double ball-and-socket articulation of skull and neck, differentiation of

teeth (incisors, canines, cheek, teeth), limbs indirect vertical alignment beneath body, and ribs reduced in neck and lumber region (promoting flexibility).

13.Chlorophytes, or green algae, are considered ancestral to land plants because of chlorophytes’ adaptation to freshwater and presence of chlorophyll (green pigment).

14.The vascular system in plants was a key step in evolution of land-dwelling species because it allowed conduction of water and dissolved minerals and gave strength to the plant so it could withstand gravity’s force and wind. The first plant to make this transition was Cooksonia, small, leafless stems that were thin and evenly branching (with branches surmounted by sporangia). Aglaophyton and Rhynia which followed had woody, vascular tissue.

15. Synapsid reptiles have a single, lower temporal opening (fenestra) on each side of the skull.

16.a and e

17.a

18.b and c

19.d

20.d

21.e

22.b

23.a

24.d

25.e

26.a

Chapter Activities

Student activities for in-depth learning.

1. Using the resources on Anomalocaris at http://www.trilobites.info/anohome.html, write a description of this unusual looking arthropod. In your description, note what uses the various features of Anomalocaris’ body plan might have been. Make a sketch of Anomalocaris and label the parts. When did this arthropod live and where has it been found?

2. Use the web resources at the web pages on placoderms located at the University of California, Berkeley, Museum of Paleontology web site as follows: http://www.ucmp.berkeley.edu/ vertebrates/basalfish/placodermi.html. What is the nature of a placoderm? What is the geological range of this fish? Make a sketch of the bony skull of the placoderm. Why was bony armor of importance to such fish at this time in geological history?

CHAPTER 12—LIFE OF THE PALEOZOIC

CHAPTER OVERVIEW

The evolution of early soft-bodied life Proterozoic forms is compared with the diversification of harder shelled Paleozoic forms. The evolution of those Paleozoic (Cambrian through Permian) forms exhibited an exponential expansion of life. This increase in the invertebrate phyla is prominently noted during Cambrian in shell-bearing trilobites and brachiopods. Cambrian history of the Burgess Shale Fauna is discussed in terms of one of its most important members, Pikaia, the earliest known member of the phylum chordata. Several other interesting members of the Burgess Shale are also described. The development of unicellular animals (protistans) and Paleozoic metazoan invertebrates is also detailed.

The evolutionary history of jawless fish beginning during Silurian to their dominance in the seas during Devonian is traced. Devonian is known as the “Age of Fish.” With the domination of the sea by fish; the first land animals, the ichthyostegids, made their appearance only to be foreshadowed by the amniotes that become more dominant. The reptiles dominance on land during Late Paleozoic and the anatomical characteristics shared by reptiles, therapsids, and mammals is discussed. Other major advances include receptaculids (green algae), and tracheophytes (trees, ferns, and flowering plants). The earliest evidence of the invasion of the continent by plants is by tetrads during Ordovician. This chapter concludes with a discussion of worldwide extinctions during Late Ordovician, Late Devonian, and Late Permian with supportive evidence given for those extinctions.

LEARNING OBJECTIVES

By reading and completing information within this chapter, you should gain an understanding of the following concepts:

Explain the significant changes in the fossil record in comparing Precambrian with Paleozoic.

Explain the importance of the Burgess Shale, both morphologically as a fossil form of chordate and as a stratigraphic marker.

Describe some morphological differences in the following Paleozoic

organisms: Protista, Foraminifera, radiolarians, archaeocyathids, Porifera, Cnidaria , Bryzoa, Brachiopoda, Mollusca, Arthropoda, Echinodermata, and graptolites.

Trace the evolutionary history of fish from an early form such as the lancelet (Branchiostoma), Ostrocoderms, Acanthodians, and Placoderms to the two major groups, Chondrichthyes (cartilaginous fish) and Osteichthys (bony skeleton forms).

Describe the evolutionary history of amphibians, including the characteristics they share with fish and reptiles.

Describe the significance of the amniotic egg in the evolutionary transition of amphibians to reptiles.

Describe the three anatomical traits possessed by therapsids that suggest they are on the main line of evolution toward mammals.

Describe the characteristics of receptaculids, chlorophytes, bryophytes, and tracheophytes in the development of land plants.

Explain some of the possible causes of mass extinctions where nearly half of all marine and terrestrial life forms became extinct by the end-Permian.

CHAPTER OUTLINE

I. Animals With Shells Proliferate — and So Does Preservation

II. The Cambrian Explosion of Life: Amazing Fossil Sites in Canada and ChinaA. The Burgess Shale FaunaB. The Chengjang Fauna

III. Continuing Diversification: Each Creature Found Its Ecological Niche

IV. Protistans: Creatures of a Single CellA. ForaminiferaB. Radiolaria

V. Marine Invertebrates Populate the SeasA. Cup Animals: ArchaeocyathidsB. Sponges: Phylum PoriferaC. Corals and Other CnidariaD. Moss Animals: BryozoaE. BrachiopodsF. Mollusks: Clams, Snails, Squid, and KinG. Arthropods: Jointed Bodies and LimbsH. Spiny-Skinned Animals: EchinodermsI. The Echinoderm-Backbone ConnectionJ. Graptolites

VI. Advent of the Vertebrates

VII. The Rise of FishesA. Agnathids (Jawless Fish)B. Evolution of the JawC. Acanthodians and Placoderms (Fish with Jaws)D. Chondrichthyes (Fish with Cartilaginous Skeletons)E. Osteichthyes (Fish with Bony Skeletons)

VIII. Conodonts: Valuable but Enigmatic Fossils

IX. Advent of TetrapodsA. Coming Ashore: First Four-Legged VertebratesB. Amniotes: Reptiles, Birds, and Mammals

X. Plants of the PaleozoicA. Land Plants

XI. Mass ExtinctionsA. Late Ordovician ExtinctionsB. Late Devonian ExtinctionsC. Late Permian Extinctions — Terrestrial Causes?D. Late Permian Extinctions — Extraterrestrial Cause?

KEY TERMS (pages given in parentheses)

acanthodians (366): The earliest known vertebrates (fishes) with a movable, well-developed lower jaw, or mandible; hence, the first jawed fishes.

actinopterygian fish(366): A division of bony fish—ray—fin forms. They lack a muscular base to their paired fins which are thin structures supported by radiating rods or rays. They also lack paired nasal passages that open into the throat.

Agnathans (364): Early agnathids are collectively termed ostracoderms (“shell skins”). The oldest armored forms were present during Paleozoic. Some lacked heavy bony armor. The diverse forms also include unarmored forms. ammonoid (351): An extinct group (subclass) of cephalopods, with coiled, chambered conch(s) and having septa with crenulated margins.

amniotic egg (337): Egg produced by reptiles, birds, and monotremes in which the developing embryo is protected by an elaborate arrangement of shell membranes, yolk sac, amnion, and allantois.

amniotic membrane (363): Membrane which allows oxygen to enter but which retains water. The membrane encloses the embryo in a cushioning, watery environment.

amniotic vertebrate (363): Higher vertebrates that have evolved internal fertilization and an amniotic egg.

antiarch (363): A heavily armored placoderm that had mud-grubbing habits.

archaeocyathid (345): A group of extinct marine organisms having double, perforated, calcareous, conical-to-cylindrical walls. Archaeocyathids lived during Cambrian.

arthrodire (366): (Latin: jointed neck.) The name refers to a ball-and-socket joint between shoulder and head that allowed the head to be rotated backward. A member of the placoderms; arthrodires were the most formable of the plate-skinned fish that were carnivorous.

arthropod (351): An enormous phylum that includes such living animals as lobsters, spiders, insects, and a host of other animals that possess chitinous exterior skeletons, segmented bodies, paired and jointed appendages, and highly developed nervous systems and sensory organs. Members of arthropoda that have left a particularly significant fossil record are the trilobites, ostracods, and eurypterids.

asteroidea (356): A member of phylum Echinodermata that are abundant and useful in geologic studies. Includes the starfish.

basal tetrapod (337): Includes amphibians. Basal tetrapod is a term applied to the earliest four-legged amphibians that walked on land, inhabited lakes, streams, and laid eggs that survived only in water.

bioturbation (343): The disturbance of sediment by burrowing, boring, and sediment-ingesting organisms.

Bivalvia (Pelcypoda) (350): Class of mollusks which includes clams, oysters, and mussels. They are characterized by layered gills, a muscular foot, a bi-lobed mantle, and the absence of a definite “head.” Members of the class made their first appearance during Cambrian, but did not become notably abundant until Pennsylvanian and Permian when they populated the shallow seas of the time.

Blastoidea (356): Sessile (attached) Paleozoic echinoderms having a stem and an attached cup or calyx composed of relatively few plates.

blastopore (359): A group of cells that form inward on the blastula to form an opening called the blastopore. In echinoderms and chordates the blastopore develops into the anus.

blastula (359): In the early development of a chordate and echinoderm embryo a small sphere of cells that are formed.

brachiopod (348): Bivalved (double-shelled) marine invertebrates. They were particularly common and widespread during Paleozoic and persist in fewer numbers today.

bryophyte (375): Today’s land plants that include mosses, liverworts, and hornworts.

bryozoan (347): A phylum of attached and incrusting colonial marine invertebrates. Minute, bilaterally symmetric animals that grow in colonies, which frequently appear twig-like when viewed without the aid of a magnifier.

Burgess Shale fauna (338): Exposure that contains one of the most important faunas in the fossil record. The fossils in the Burgess Shale are reduced to shiny, jet like impressions on the bedding planes of the black rock. Most of them are the remains of animals that lacked shells. Altogether, they form an extraordinary assemblage that includes four major groups of arthropods (trilobites, crustaceans, and members of the taxonomic groups that include scorpions and insects) as well as sponges, onycophorans, crinoids, sea cucumbers, chordates, and many species that defy placement in any known phyla.

cephalopod (350): May be the most complex of all the mollusks. This marine group is represented by the squid, cuttlefish, octopod, and the attractive chambered nautilus.

ceratite (351): One of the three larger groups of ammonoid cephalopods having sutural complexity, intermediate between goniates and ammonites.

Chengjian fauna (343): A fauna that resembles that of the Burgess Shale, but that are older and better preserved. Many of the normally soft-bodied worms, eyes, segmentation, digestive organs are preserved. The Chengjiang fossils are dated at 535 million years old. They also include the world’s oldest fish.

chlorophyte (374): Green algae. The close relationship between chlorophytes and land plants is suggested by their adaptation not only to freshwater bodies but to moist soil as well. Both green algae and land plants possess the same kind of green pigments and produce the same kind of carbohydrate during photosynthesis. During Early Paleozoic, chlorophytes were probably symbiotically joined by fungi to form lichens.

chordate (342): Are unique creatures that in some stages in their development, have a notochord (an internal supportive rod) and a nerve cord that extend along the dorsal (upper) side of the notochord. In humans, the notochord is replaced with a series of vertebrae, therefore are called vertebrates.

Cnidaria (346): A phylum including sea anemones, sea fans, jellyfish, the tiny Hydra, and reef-forming corals. This phylum is known for the great diversity and beauty of its members. The body wall is composed of an outer layer of cells, the ectoderm; and inner layer, the endoderm; and a thin, non-cellular intermediate layer, the mesoglea.

cnidocyte (347): Members of Cnidaria have stinging cells (cnidophytes) that when activated can inject a paralyzing poison, e.g., jelly fish.

conodont elements (370): Small, tooth-like fossils composed of calcium phosphate and found in rocks ranging from Cambrian to Triassic. Although the precise nature of the conodont-producing organism has not been determined, this uncertainty does not detract from their usefulness as guide fossils.

crinoid (357): Stalked echinoderm with a calyx composed of regularly-arranged plates from which radiate arms for gathering food.

crinoid (357): Crinoids are the most abundant stalked echinoderm. They range from Cambrian to present. Some Ordovician, Silurian, and Carboniferous limestones contain such great quantities of crinoid plates that they are called “crinoidal limestones.”

Crinoidea (356): One of the many classes of the phylum Echinodermata. Stalked echinoderms, usually called crinoids.

crossopterygian fish (370): That group of choanichthyan fishes ancestral to earliest amphibians and characterized by stout pectoral and pelvic fins as well as lungs.

deuterostome (359): Echnoderms and chordates are deuterostomes since they form an anus from an opening called a blastopore.

Diploporita (356): One of the many classes of the phylum Echinodermata. These echinoderms have unusual patterns of pores.

dipnoan fish (367): An order of lungfishes with weak pectoral and pelvic fins; not considered ancestral to land vertebrates.

echinoderm (356): The large group (phylum Echinodermata) of marine invertebrates characterized by prominent pentamerous symmetry and skeleton frequently constructed

of calcite elements including spines. Cystoids, blastoids, crinoids, and echinoids are examples of echinoderms.

Echinoidea (356): Class of the phylum Echinodermata which includes sea urchins. Echinoids were more frequent in later eras.

Edrioasteroid (356): Class of the phylum Echinodermata. Edrioasteroids are considered to be ancestral to starfish and sea urchins.

epifaunal animal (343): Organisms living on, as distinct from in, a particular body of sediment or another organism. They live on top of the sediment that carpets the seafloor.

eurypterid (355): Aquatic Paleozoic arthropods, superficially resembling scorpions, and probably carnivorous.

filter feeders (343): Organisms that strained tiny bits of organic matter or microorganisms from the water.

foraminifera (343): An order of mostly marine, unicellular protozoans that secrete tests (shells) that are usually composed of calcium carbonate.

fusulinid (343): Primarily spindle-shaped foraminifers with calcareous, coiled tests divided into a complex of numerous chambers. Fusulinids were particularly abundant during Pennsylvanian and Permian.

gastropod (350): Class of mollusk first appearing in Lower Cambrian strata. The earliest forms constructed small, depressed conical shells. During Late Cambrian and Ordovician, gastropods with the more familiar coiled conchs became commonplace. By Pennsylvanian, gastropods had become abundant and diverse. The oldest known air-breathing (pulmonate) gastropods appeared. Permian ended with widespread extinctions among marine invertebrates, and many families of gastropods were decimated.

goniatite (351): One of the three large groups of ammonoid cephalopods with sutures forming a pattern of simple lobes and saddles and thus not as complex as either the ceratites or the ammonites.

graptolite (361): Extinct colonial marine invertebrates considered to be protochordates. Graptolites range from Late Cambrian to Mississippian.

herbivore (343): Animals that consume plants exclusively.

HOX genes (338): Sequences of genes that control the development of entire regions of the body.They lay out the basic body architecture of many animals. Very small changes in HOX genes are potentially able to cause sudden and major evolutionary change.

hypercapnia (380): Carbon dioxide poisoning.

ichthyostegid (372): The fossil record for amphibians begins with this group. These creatures retained many features of their fish ancestors.

infaunal animal (343): Organisms that live and feed within bottom sediments. They burrow into soft sediment for food and protection.

labyrinthodont (372): Amphibians that followed the ichthyostegids fall within a group termed labyrinthodonts. During Carboniferous, large numbers of labyrinthodonts walled in swamps and streams, eating insects, fish, and one another. A labyrinthodont that exemplifies the culmination of the lineage is Eryops. Labyrinthodonts declined during Permian, and only a relatively few survived into Triassic.

lycopsid (375): Leafy plants with simple, closely spaced leaves bearing sporangia on their upper surfaces. They are represented by living club mosses and vast numbers of extinct Late Paleozoic “scale trees.”

mass extinctions (337): Marked by times of sudden worldwide extinctions of large number of animals and some plant populations. During Paleozoic, mass extensions occurred during Late Ordovician, Devonian, and Permian.

mollusk (349): Any member of the invertebrate Phylum Mullusca, including bivalves (pelecypods) cephalopods, gastropods, scaphopods, and chitons.

monoplacophoran (349): Primitive marine molluscans with simple, cap-shaped shells.

nautiloid (351): A subclass of cephalopods having straight or gently undulating sutures.

non-amniotic vertebrates (363):

notochord (342): A rod-shaped cord of cartilage cells forming the primary axial structure of the chordate body. In vertebrates, the notochord is present in the embryo and is later supplanted by the vertebral column.

Ophiuroidea (356): A member of Phylum Echinodermata. Class Ophiuroidea include brittle stars.

osteichthyes (365): Are the bony fish forms that represent the most numerous, varied and successful of all aquatic vertebrates. They also play a key role in the evolution of testrapods (four-legged animals).

ostracod (355): Bean-shaped arthropod of Paleozoic seas. They are bivalved resembling a small clam. The bivalved carapace encloses a segmented body from which extend seven pairs of jointed appendages. Valves are composed of both chitin and calcium carbonate and are hinged along the dorsal margin. Ostracods first appeared during Early Ordovician and continue in relative abundance to the present day. They occur in both marine and freshwater sediments.

ostracoderm (365): Extinct jawless fishes of Early Paleozoic.

Pelecypoda (350): A class of mollusks that includes clams, mussels, scallops, and oysters. They originated during Cambrian, but did not become abundant until Carboniferous and Permian.

pelycosaur (372): These Permian reptiles had several mammalian skeletal characteristics, they are thought to be early representatives of the reptilian group which advanced, mammal-like reptiles known as therapsids arose.

placoderm (366): Extinct primitive Paleozoic jawed fishes.

placophoran (349): Relatively primitive mollusks that have multiple-paired gills and, in shelled forms, a creeping foot much like that seen in snails. The most familiar is the polyplacophorans, represented by chitons, which possess eight overlapping plates covering an ovoid, flattened body.

polyplacophorans (349): Are primitive mollusks that have multiple-paired gills and, in shelled forms, a creeping foot similar to snails. Chitons are polyplcophorans. Their fossil record extends from Cambrian to present.

Porifera (345): Phylum containing sponges. Sponges appear to have evolved from colonial flagellated unicellular creatures and thus provide insight into how the transition from unicellular to multicellular animals may have occurred. Sponges have always been predominantly marine creatures, although a few modern species live in fresh water. Although sponges vary greatly in size and shape, their basic structure is that of a highly perforated vase modified by folds and canals. The body is attached to the seafloor at the base, and there is an excurrent opening, or osculum, at the top. The walls consist of two layers of cells. Facing the internal space is a layer of collar cells (choanocytes), and on the outside is a protective wall of flat cells that resemble the bricks of a worn masonry pavement. Between these two layers one finds a gelatinous substance called mesenchyme. Sponges lack true organs. Water currents moving through the sponge are created by the beat of flagellae. The currents bring in suspended food particles, which are ingested by the collar cells. In a simple sponge, water enters through the pores, flows across sheets of choanocytes in the central cavity, and passes out through the osculum.

protostome (359): Animals that would include arthropods, mollusks, and annelid worms in which the blastopore develops into a mouth.

pterobranchs (362): A primitive living chardate that secretes tiny enclosed tubes.

radiolaria (344): Protozoa that secrete a delicate, often beautifully filigreed skeleton of opaline silica.

receptaculid (374): Relatively common group of marine algal fossils found within Lower Paleozoic rocks. Receptaculids are lime-secreting green algae of the family

Dasycladaea. Although most frequently found within Ordovician rocks, members of this group also occur sparsely within Silurian and Devonian strata.

sarcopterygian fish (366): Lobe-finned bony fish including air-breathing crossopterygion fish that had a pair of openings in the roof of the mouth that led to external nostrils. This allowed sarcopterygion to rise to the surface and take in air. This eventually led to functional lungs.

sediment feeders (343): Organisms that ingest mud of the seafloor through their digestive tracts to extract nutrients, as earthworms today.

small shelly fossils (337): Fossils that date back to Late Neoproterozoic. Include shells and skeletal elements of mollusks and sponges. It also includes small invertebrates of uncertain classification that secreted tabular or cap-shaped shells.

stromatoporoid (345): A group of Early Paleozoic sclerosponges of particular interest because of their reef-building capabilities. These organisms constructed fibrous, calcareous skeletons of pillars and thin laminae that can nearly always be found in reef-associated Silurian and Devonian carbonate rocks.

synapsid (372): Reptiles having only one temporal opening which is located low on the skull (below the squamosal and post orbital bones): belongs to the subclass Synapsida.

tetrapod (337, 363): Vertebrates that include both water-dwelling and land-dwelling forms that walk on four legs.

therapsid (337, 374): An order of advanced mammal-like reptiles. They were widely dispersed during Permian and Triassic. They were predominantly small to moderate-sized animals that displayed at least the beginnings of several mammalian skeletal traits. There were fewer bones in the skull than generally found in reptile skulls, and there was a mammal-like enlargement of the lower jaw bone (dentary) at the expense of more posterior elements of the jaw. A double ball-and-socket articulation had evolved between the skull and neck. Teeth showed a primitive but distinct differentiation into incisors, canines and cheek teeth. The limbs were in more direct vertical alignment beneath the body, and the ribs were reduced in the neck and lumbar region for greater overall flexibility. Therapsids became extinct early in the Jurassic. Before they died out, they gave origin to the early mammals.

tracheophyte (375): A member of today’s land plants includes trees, ferns, and flowing plants. Tracheophytes have a vascular tissue that transports water and nutrients from one part of the plant to another.

trilobite (351): Swimming or crawling arthropods that take their name from division of the dorsal surface into three longitudinal segments, or lobes. The skeleton was composed of chitin strengthened by calcium carbonate in parts not requiring flexibility. Growth was accomplished by molting. Although many trilobites were sightless, the majority had either single-lens eyes or compound eyes composed of a large number of discrete visual bodies. Earliest forms had small pygidian and a large number of thoracic segments suggesting evolution from annelid worms.

vertebral column (363): The segmented backbone of the vertebral animal.

vertebrate (342, 358): Animals having a segmented backbone, or dorsal vertebrae column. The vertebral column is composed of individual vertebrae. Arches of the vertebrae encircle and protect a hollow spinal cord (nerve cord). In addition, vertebrates have a cranium or skull that houses a brain.

water vascular system (356): A system possessed by phylum Echinodermata in which a system of soft-tissue tubes function in respiration and locomotion.

Life of the Paleozoic

2 PALEOZOIC OVERVIEW FIGURE 10-1 Major events of the Paleozoic Era.

3 PALEOZOIC FOSSIL RECORD In Paleozoic rocks, we find abundant fossils of multicellular organisms bearing shells. The fossil record is much improved at the beginning (the base of) Paleozoic strata. The pace of evolution appears to have quickened in the Paleozoic

4 PALEOZOIC INVERTEBRATES Representatives of most major invertebrate phyla were present during Paleozoic, including sponges, corals, bryozoans, brachiopods, molluscs, arthropods, and echinoderms.

Almost all of the common invertebrate phyla in existence today had appeared by Ordovician.

5 PALEOZOIC VERTEBRATES Vertebrates evolved during Paleozoic, including: Fishes Amphibians Reptiles Synapsids ("mammal-like reptiles") The first vertebrates were jawless fishes, which are found in rocks as old as Cambrian in China.

6 PALEOZOIC VERTEBRATES An advanced lineage of fishes with primitive lungs and stout fins gave rise to the four-legged animals or tetrapods.

The transition from water-dwelling vertebrates to land-dwelling vertebrates depended on the evolution of the amniotic egg.

7 PALEOZOIC PLANTS The first primitive land plants appeared near the end of Ordovician. Vascular plants expanded across the land, forming great forests during Devonian. The plants progressed from seedless, spore-bearing plants to plants with seeds but no flowers (gymnosperms).

8 PALEOZOIC EXTINCTIONS Several mass extinctions occurred during Paleozoic, including the largest extinction of all at the end of Permian.

Other mass extinctions occurred at the end of Ordovician and Devonian.

9 PALEOZOIC LIFE Summary of invertebrate phyla

10 PALEOZOIC LIFE CONT. Summary of invertebrate phyla

11 ADAPTIVE RADIATIONS AND EXTINCTIONS Paleozoic was a time of several adaptive radiations and extinctions. Many geologic periods began with adaptive radiations (times of rapid evolution). Several periods ended with extinction events of varying severity. The extinction event at the end of Permian was the most extensive mass extinction in the history of life.

12 DIVERSITY DURING PALEOZOIC Red arrows mark extinction events.

FIGURE 12-94 13 SOFT-BODIED ANIMALS Multicellular animals evolved during Precambrian. Soft-bodied Ediacaran-type organisms ranged into Cambrian. Soft-bodied fossils are infrequently preserved.

Preservation improved with the origin of hard parts.

14 The first animals with shells are called small shelly fossils.

Small shelly fossils are found at the base of Cambrian, and during Late Neoproterozoic.

Most disappeared during the Early Cambrian.

SMALL SHELLY FOSSILS

FIGURE 12-2 15 SMALL SHELLY FOSSILS Many had phosphatic shells, few mm in size. Shells and skeletal remains of primitive molluscs, sponges, and animals of uncertain classification, such as Cloudina, that secreted a calcareous tube. FIGURE 12-1 Tiny shell-bearing fossils from the Late Precambrian and Early Cambrian in Siberia. 16 CAMBRIAN DIVERSIFICATION The initial Paleozoic diversification is known as "the Cambrian explosion." Abrupt appearance of many types of animals about 535 million years ago, followed by rapid evolution.

During that episode of explosive evolution, all major invertebrate phyla appeared in the fossil record (except Bryozoa). 17 CAMBRIAN SUBSTRATE REVOLUTION Infaunal, burrowing animals evolved rapidly during Cambrian, as indicated by trace fossils and bioturbation (disruption of sedimentary structures by biological activity) of sediments.

The dramatic change in the character of the seafloor sediments (from undisturbed to highly burrowed) has been called the "Cambrian substrate revolution."

18 WHY THE CAMBRIAN EXPLOSION? No satisfying answers to why life diversified at the beginning of the Cambrian. The answer likely involves a number of factors. Climate conditions became more favorable after the end of the Neoproterzoic glaciation. Perhaps the glaciation produced an extinction event in the Ediacaran animals. Extinction events of the Phanerozoic have been followed by rapid adaptive radiation 19 SOFT-BODIED FOSSILS IN THE BURGESS SHALE The extraordinarily well-preserved Middle Cambrian Burgess Shale fauna of Canada provides a window into the past to view the spectacular diversity of Middle Cambrian. Many soft-bodied organisms are preserved in black shale, along with the soft parts of animals with shells, such as legs and gills of trilobites. 20 SOFT-BODIED FOSSILS IN THE BURGESS SHALE The significance of the Burgess Shale is that is records soft-bodied organisms, and the soft parts of organisms with shells. The finely detailed preservation reveals the extraordinary diversity and evolutionary complexity

that existed near the beginning of Paleozoic. 21 STRATIGRAPHIC SETTING OF THE CAMBRIAN BURGESS SHALE FIGURE 12-5 The Burgess Shale fauna. 22 ANIMALS IN THE BURGESS SHALE 1.Several groups of arthropods, including trilobites and crustaceans 2.Sponges 3.Onycophorans 4.Crinoids 5.Molluscs 6.Corals 7.Three phyla of worms 8.Chordates (Pikaia) 9.Many others 23

Location of the Burgess Shale fauna in British Columbia, Canada C = Onycophoran, Aysheaia, intermediate in evolution between segmented worms and arthropods. D = Arthropod Leanchoila E= Arthropod Waptia

ANIMALS IN THE BURGESS SHALE FIGURE 12-5 The Burgess Shale fauna. 24 ANIMALS IN THE BURGESS SHALE: CHORDATES Chordates have a notochord or dorsal stiffening rod associated with a nerve chord, at some stage in their development. In vertebrates, the notochord is surrounded by and usually replaced by a vertebral column during embryonic development. Vertebrates are chordates, but Pikaia pre-dates the evolution of vertebrae. It is thought that vertebrates evolved from organisms similar to Pikaia.

Pikaia is a fish-like lower chordate from the Burgess Shale. Modern representatives are called lancelets, such as the genus Amphioxus.

FIGURE 12-13 25 PREDATORS IN THE CAMBRIAN SEAS The giant predator of the Cambrian seas, Anomalocaris, up to 60 cm long. Predators would have caused selective pressures on prey. The need to avoid being eaten probably encouraged the evolution of hard protective shells. Predation probably also caused an increase in diversity of prey, as they evolved to better survive predation. FIGURE 12-8 Anomalocaris, “invertebrate equivalent of the dinosaurs.” 26 OTHER BURGESS SHALE ANIMALS Marrella, a "lace crab," is common in the Burgess Shale. Hallucigenia, an onycophoran, was originally interpreted to walk on its spines, until claws were discovered on its "tentacles."

FIGURE 12-10 FIGURE 12-11 27 EXCEPTIONAL PRESERVATION Fossil sites containing abundant fossils with extraordinary preservation are called lagerstätten.

Both the Burgess Shale fauna and the Chengjiang fauna from China are considered to be lagerstätten. 28 THE CHENGJIANG FAUNA In 1984, the Lower Cambrian Chengjiang fossil site was discovered in Yunnan Province, China. More than 100 species of invertebrates have been found, with extraordinary preservation, including many soft bodied forms. 29 THE CHENGJIANG FAUNA Jelly fish Annelid worms Cnidaria Porifera (sponges) Brachiopods Arthropods Early chordates similar to Pikaia The world's oldest known fish (Myllokunmingia) Other species of unknown phyla 30 OLDEST KNOWN FISH The world's oldest known fish, Myllokunmingia, from the Maotianshan Shale near Chengjiang, in the Yunnan Province of China. 535 million years old. 31 ORDOVICIAN DIVERSITY Following a slight dip in diversity at the end of Cambrian, Ordovician seas experienced renewed diversification. Global diversity tripled over a 25 million year time interval. The number of genera increased rapidly, and the number of families increased from about 160 to 530. The increase was particularly notable among trilobites, brachiopods, bivalve molluscs, gastropods, and corals.

Why diversify? Fragmented continents Extensive seafloor spreading Extensive warm nutrient rich seas fostering plankton growth resulting in an expansion of the base of the food chain. 32 LATE ORDOVICIAN EXTINCTION An extinction event at the end of Ordovician led to an abrupt decline in diversity. This extinction event was apparently related to the growth of glaciers in Gondwana, coupled with a reduction in shallow water habitat associated with the lowering of sea level. 33 DIVERSITY AND EXTINCTION DURING PALEOZOIC Red arrows mark extinction events 34 SILURIAN DIVERSITY Diversification of marine animals occurred again at the beginning of Silurian. The period ended with only a slight drop in diversity. 35 DEVONIAN DIVERSITY During Devonian, there was continued diversification, but this ended with another fairly large extinction event, which extended over about 20 million years. Roughly 70% of marine invertebrates disappeared.

Because of the long duration, the extinction is unlikely to have been caused by a sudden, catastrophic event. 36 CARBONIFEROUS-PERMIAN DIVERSITY During Early Carboniferous, diversity once again increased.

Diversity of marine animals remained fairly constant throughout Carboniferous and Permian. Late Permian is marked by a catastrophic extinction event which resulted in the total disappearance of many animal groups. 37 OVERVIEW OF CHANGES IN DIVERSITY THROUGH TIME 1.Several Paleozoic periods ended with extinction events 2.The beginning of most Paleozoic periods were marked by adaptive radiations 3.Maximum diversity in Paleozoic seas was maintained roughly constant at between 1000 and 1500 genera 4.The largest extinction occurred at the end of Permian 38

5.Recovery of diversity during Mesozoic was slow 6.Diversity increased rapidly during Cretaceous 7.Another mass extinction occurred at the end of Cretaceous 8.Diversity increased extremely rapidly, at unprecedented rates, at the beginning of Cenozoic 9.Diversity during Cretaceous and Cenozoic was much greater than during Paleozoic OVERVIEW OF CHANGES IN DIVERSITY THROUGH TIME 39 Red arrows mark extinction events OVERVIEW OF CHANGES IN DIVERSITY THROUGH TIME 40 UNICELLULAR ORGANISMS IN THE PALEOZOIC SEAS The principal groups of Paleozoic unicellular animals with a significant fossils record are the foraminifera and the radiolaria, which belong to Phylum Sarcodina.

These organisms are unicellular eukaryotic organisms, and belong to Kingdom Protista. 41 FORAMINIFERA Name: Foraminifera means "hole bearer." Chief characteristics: Unicellular. Related to the amoeba, with pseudopods. Foraminifera build tiny shells (called tests) which grow by adding chambers. Some species (called agglutinated foraminifera) construct tests of tiny particles of sediement. This is the most primitive test. Other forams construct tests of calcium carbonate. 42 FORAMINIFERA Geologic range: Cambrian to Holocene. Modes of life: Benthic or benthonic (bottom dwellers) Planktic or planktonic (floaters). 43 FUSULINID FORAMINIFERA (FUSULINIDS)

Fusulinids were abundant during Late Paleozoic (primarily Pennsylvanian and Permian). Their tests were similar in size and shape to a grain of rice. Their internal structure is complex and used to distinguish different species. Important guide fossils during Pennsylvanian and Permian because they evolved rapidly, were abundant, and widespread geographically. 44 RADIOLARIA Chief characteristics: Unicellular. Test or shell composed of opaline silica Ornate lattice-like skeleton Often spherical or radially symmetrical with spines Geologic range: Precambrian or Cambrian to Holocene. Rare during Early Paleozoic. More abundant during Mesozoic and Cenozoic. Mode of life: Planktonic. Marine only. 45 RADIOLARIA AND THE ROCK RECORD Radiolarians are important constituents of chert at certain times in geologic history.

Their tests accumulate on the seafloor today to form radiolarian ooze, particularly in deep water, where any calcium carbonate shells would be dissolved. 46 MARINE INVERTEBRATES IN THE PALEOZOIC SEAS The fossils of shell-bearing invertebrates that inhabited shallow seas are common in Paleozoic rocks. Archaeocyathids, sponges, corals, bryozoans, trilobites, molluscs, and echinoderms. Many were benthic (bottom dwellers), but others, such as graptolites, were planktonic. Currents carried them over wide areas. As a result, they are useful index fossils for global stratigraphic correlation. 47 PHYLUM ARCHAEOCYATHA Name means "ancient cup" Chief characteristics: Conical or vase-shaped skeletons made of calcium carbonate. Double-walled structure with partitions and pores. Geologic range: Cambrian only. Extinct. Mode of life: Attached to the sea floor. Reef-builders. FIGURE 12-17 Archaeocyathid skeleton. 48 PHYLUM PORIFERA - THE SPONGES Name means “pore-bearing,” or covered by tiny pores. FIGURE 12-21 Schematic diagram of a sponge with the simplest type of canal system. FIGURE 12-18 Early Paleozoic sponges. 49 PHYLUM PORIFERA - THE SPONGES Chief characteristics: Globular, cylindrical, conical or irregular shape. Basic structure is vase-like with pores and canals. Interior may be hollow or filled with branching canals. Solitary or colonial. Skeletal elements are called spicules, and they may be separate or joined. Composition may be calcareous, siliceous or organic material called spongin.

50 PHYLUM CNIDARIA Corals, sea fans, jellyfish, and sea anemones. Name: Cnidaria are named for stinging cells called cnidoblasts or cnidocytes. Many are soft-bodied but only those which form hard skeletal structures are readily preservable as fossils. FIGURE 12-23 Common cnidarians. 51 PHYLUM CNIDARIA Geologic range: Late Precambrian (Proterozoic) to Holocene for the phylum.

The first corals were the tabulates.

Mode of life: Corals live attached to the sea floor, primarily in warm, shallow marine environments.

52 PHYLUM CNIDARIA – CHIEF CHARACTERISTICS 1.Radial symmetry 2.Mouth at the center of a ring of tentacles. FIGURE 12-24 53 PHYLUM CNIDARIA – CHIEF CHARACTERISTICS 3.Body form may be polyp (attached to the bottom, with tentacles on top) or medusa (free-swimming, jellyfish). Diorama photograph courtesy of the U.S. National Museum of Natural History/ Smithsonian Institution.) 54 CHIEF CHARACTERISTICS OF CORALS 1.May be solitary or colonial. Colonies are composed of many polyps living together. 2.Hard calcareous skeleton. The skeletal parts formed by polyps are called corallites. 3.The "cup," in which an individual coral polyp sits, is called the theca. Each theca is small, and roughly circular or hexagonal. 4.The theca is divided internally by vertical partitions called septae, arranged in a radial pattern. 55 CHIEF CHARACTERISTICS OF CORALS 5.Types of corals are distinguished by presence or absence, and number of septae: Rugose corals (or tetracorals) have septae arranged in multiples of four. Tabulate corals lack septae. Mesozoic and Cenozoic scleractinian corals (or hexacorals) have septae arranged in multiples of six. 56 RUGOSE CORALS Most rugose corals are solitary and conical (shaped like ice cream cones). Septae are visible in the circular opening of the cone. Some rugose corals are colonial, having hexagonal corallites with septae (such as Hexagonaria from Devonian of Michigan). 57 RUGOSE CORALS Geologic range: Ordovician to Permian - all extinct.

Rugose corals were abundant during Devonian and Carboniferous, but became extinct during Late Permian. 58 TABULATE CORALS Tabulate corals are colonial and resemble honeycombs or wasp nests.

They lack septae. They have horizontal plates within the theca called tabulae. Tabulae are one of the main features of the tabulate corals. 59 TABULATE CORALS Geologic range: Ordovician to Permian - all extinct. The principal Silurian reef formers. They declined after Silurian and their reef-building role was assumed by the rugose corals. 60 MODERN CORALS Modern corals are scleractinian corals. Scleractinian corals have septae are arranged in multiples of six, and are sometimes called hexacorals. Scleractinian corals did not appear until after Paleozoic Geologic range: Triassic to Holocene. 61 PHYLUM BRYOZOA Name: Name means "moss" (bryo) + "animal" (zoa). Chief characteristics: Colonial (many microscopic individuals living physically united adjacent to one another). The individuals are called zooids, and they are housed in a hard "capsule" called a zooecium. The colony is called a zoarium. 62 PHYLUM BRYOZOA Individual zooecia (plural of zooecium) are very tiny (about the size of a pin-hole, a millimeter or less in diameter). They are just large enough to be seen with the unaided eye.

Bryozoans may be distinguished from corals because of the apertures in the skeleton are much smaller. 63 PHYLUM BRYOZOA The bryozoan colony may resemble lace or a tiny net, may be delicately branching, finger-like, circular or dome-shaped. There are more than 4000 living species of bryozoans, and nearly 16,000 fossil species. Archimedes, from Mississippian rocks, has a cork-screw-like central axis with a fragile net-like colony around the outer edge. 64 PHYLUM BRYOZOA Geologic range: Ordovician to Holocene. Mode of life: Widespread in marine environments. A few live in freshwater lakes and streams.

65 PHYLUM BRACHIOPODA Name: Name means "arm" (brachio) + "foot" (pod). Chief characteristics: Bivalved (two shells), each with bilateral symmetry. The plane of symmetry passes through the center of each shell or valve. The two valves differ in size and shape in most. Sometimes the larger valve will have an opening near the hinge line through which the pedicle extended in life. 66 PHYLUM BRACHIOPODA Soft parts include a lophophore consisting of coiled tentacles with cilia. The lophophore circulates water between the two valves, distributing oxygen and flushing out carbon dioxide. Water

movements caused by the lophophore also transport food particles toward the mouth. 67 PHYLUM BRACHIOPODA Mode of life: Shallow marine environments. Generally attached to the sea floor. Inarticulate brachiopods are known to live in burrows in the sediment. Brachiopods are filter feeders. FIGURE 12-28 68 INARTICULATE BRACHIOPODS Primitive brachiopods with phosphatic or chitinous valves. No hinge. Spoon-shaped valves held together with muscles and soft parts. Lingula is a well known genus Geologic range: Early Cambrian to Holocene

69 ARTICULATE BRACHIOPODS Calcareous valves attached together with a hinge consisting of teeth and sockets. Geologic range: Early Cambrian to Holocene Spiny brachiopods (called productids) are characteristic of Carboniferous and Permian. 70 PHYLUM BRACHIOPODA Geologic range:

Early Cambrian to Holocene. Very abundant during Paleozoic. A few species (belonging to only three families) remain today.

71 PHYLUM MOLLUSCA Clams, oysters, snails, slugs, Nautilus, squid, octopus, cuttlefish Name: Mollusca means " soft bodied."

72 PHYLUM MOLLUSCA Chief characteristics:

Soft body enclosed within a calcium carbonate shell. A few, like slugs and the octopus, have no shell. Muscular part of body of clams and snails and some other groups of molluscs is called the foot.

73 PHYLUM MOLLUSCA Geologic range: Cambrian to Holocene

Mode of life: Marine, freshwater, or terrestrial. They may: swim, float or drift, burrow into mud or sand, bore into wood or rock, attach themselves to rocks, or crawl.

74 TYPES OF MOLLUSCS 1.Monoplacophorans (Neopilina) 2.Polyplacophorans or amphineurans (chitons)

3.Bivalves or pelecypods (clams, scallops) 4.Gastropods (snails and slugs) 5.Cephalopods (squid, octopus, Nautilus) 6.Scaphopods (tusk shells)

75 CLASS MONOPLACOPHORA Chief characteristics: Single shell resembling a flattened cone or cap. Soft part anatomy shows pseudo-segmented arrangement of gills, muscles, and other organs. Suggests that the primitive mollusc was a segmented animal. Segmentation was lost secondarily. Monoplacophorans are regarded as ancestral to bivalves, gastropods, and cephalopods.

FIGURE 12-35 76 CLASS MONOPLACOPHORA Name: Monoplacophora means "single plate-bearer."

Geologic range: Cambrian-Holocene, but only known as fossils from Cambrian to Devonian. Living monoplacophorans found in deep water off Costa Rica in 1952 and named Neopilina. Considered to be a "living fossil."

77 CLASS AMPHINEURA OR POLYPLACOPHORA – THE CHITONS Chief characteristics: Chitons have 8 overlapping plates covering an ovoid, flattened body. FIGURE 12-34 A common placophoran, the Atlantic Coast chiton. 78 CLASS AMPHINEURA OR POLYPLACOPHORA – THE CHITONS Name: Polyplacophora means "many plate-bearer." Geologic range: Cambrian to Holocene

79 CLASS BIVALVIA OR PELECYPODA Clams, oysters, scallops, mussels, rudists Chief characteristics: Skeleton consists of two calcareous valves connected by a hinge. Bilateral symmetry; plane of symmetry passes between the two valves. FIGURE 12-36 Paleozoic bivalves. 80 CLASS BIVALVIA OR PELECYPODA Name: Bivalvia means " two" (bi) + " shells" (valvia).

Geologic range: Early Cambrian to Holocene

Mode of life: Marine and freshwater. Many species are infaunal burrowers or borers, and others are epifaunal.

81 CLASS GASTROPODA Snails and slugs Chief characteristics: Asymmetrical, spiral-coiled calcareous shell. Name: means "stomach" (gastro) + "foot" (pod). Geologic range: Early Cambrian to Holocene. Mode of life: Marine, freshwater or terrestrial.

82 CLASS CEPHALOPODA Squid, octopus, Nautilus, cuttlefish Name: means " head" (kephale) + " foot" (pod). Chief characteristics: Symmetrical cone-shaped shell with internal partitions called septae Shell may be straight or coiled in a spiral which lies in a plane. Smooth or contorted sutures visible on the outside of some fossils mark the place where septae join the outer shell.

83 CLASS CEPHALOPODA Geologic range: Late Cambrian to Holocene

Mode of life: Marine only; carnivorous (meat-eating) swimmers.

Types of Paleozoic cephalopods:

84 NAUTILOID CEPHALOPODS The shells of nautiloid cephalopods have smoothly curved septa, which produce simple, straight or curved sutures. Geologic range: Cambrian to Holocene

85 AMMONOID CEPHALOPODS Ammonoid cephalopods have complex, wrinkled or crenulated septa, which produce angular or dendritic sutures. Geologic range: Devonian to Cretaceous - all extinct.

86 AMMONOID CEPHALOPODS There are three basic types of sutures in ammonoid shells:

Goniatite or goniatitic (septae have relatively simple, zig-zag undulations) Ceratite or ceratitic (septae have smooth "hills" alternating with saw-toothed "valleys") Ammonite or ammonitic (septae are complexly branching and tree-like or dendritic) 87 TYPES OF SUTURES IN CEPHALOPODS FIGURE 12-39 Cephalopod suture patterns. 88 SUBCLASS COLEOIDEA Belemnoids (belemnites) Geologic range: Mississippian to Eocene - all extinct. Sepioids (cuttlefish) Geologic range: Jurassic to Holocene Teuthoids (squid) Geologic range: Jurassic to Holocene

Octopods (octopus) Geologic range: Cretaceous to Holocene 89 ORDER BELEMNOIDEA - BELEMNOIDS

The belemnoids have an internal calcareous shell (which resembles a cigar in size, shape, and color) called a rostrum The front part of this shell is chambered, as in the nautiloids and ammonoids. The rostrum is made of fibrous calcite, arranged in concentric layers. 90

CLASS SCAPHOPODA Tusk shells or tooth shells

Chief characteristics: Curved tubular shells open at both ends.

Geologic range: Ordovician to Holocene.

Mode of life: Marine. 91 PHYLUM ARTHROPODA

Insects, spiders, shrimp, crabs, lobsters, barnacles, ostracodes, trilobites, eurypterids Name: means "jointed" (arthro) + "foot" (pod). Chief characteristics: Segmented body with a hard exterior skeleton composed of chitin (organic material). Paired, jointed legs. Highly developed nervous system and sensory organs. 92

PHYLUM ARTHROPODA Geologic range: Cambrian to Holocene

Mode of life: Arthropods inhabit a wide range of environments. Most fossil forms are found in marine or freshwater sediments. 93 PALEOZOIC ARTHROPODS AND THEIR GEOLOGIC RANGES

Trilobites - Cambrian to Permian Horseshoe crabs - Silurian to Holocene Eurypterids - Ordovician to Permian Arachnids - Late Silurian to Holocene Ostracodes - Cambrian to Holocene Onychophorans - Cambrian to Holocene Insects - Devonian to Holocene 94

SUBPHYLUM TRILOBITA - TRILOBITES Chief characteristics: Body has three-lobes Skeleton composed of chitin, with calcium carbonate Body is divided into three segments: Rigid head segment - cephalon Jointed, flexible middle section - thorax Rigid tail piece - pygidium FIGURE 12-42 95 SUBPHYLUM TRILOBITA - TRILOBITES

Name: Trilobite means "three" (tri) + "lobed" (lobus). Geologic range: Cambrian to Permian Mode of life: Exclusively marine. Most were bottom dwellers living in shallow shelf environments. 96 CLASS EURYPTERIDA - EURYPTERIDS

Extinct scorpion-like or lobster-like arthropods. Predators. Up to 10 ft long. Geologic range: Ordovician to Permian. Most are Silurian or Devonian. Mode of life: Inhabited brackish estuaries. 97

CLASS ARACHNIDA - ARACHNIDS Scorpions, spiders, ticks, and mites Scorpions are the oldest arachnids with a fossil record. Scorpions had evolved by Late Silurian. The earliest ones appear to have lived in the water, because their fossils have gills. Scorpions, spiders, and mites are found in Devonian rocks. Geologic range: Late Silurian to Holocene. 98 CLASS OSTRACODA -OSTRACODES

The ostracodes are mainly microscopic in size. Tiny bivalved shell encasing a shrimp-like creature. Geologic range: Cambrian to Holocene. Mode of life: Both marine and freshwater. 99 CLASS ONYCHOPHORA Onychophorans share many characteristics of segmented annelid worms and arthropods, and are considered to be intermediate in evolution between the two groups. Geologic range: Cambrian to Holocene The onycophoran, Aysheaia 100 CLASS HEXAPODA - INSECTS

The insects are among the most diverse living group on Earth, but they are rarely found as fossils. Body is divided into three parts, head, thorax, and abdomen. Thorax has six legs. The earliest insects were wingless. Winged insects appeared by Pennsylvanian. Geologic range: Middle Devonian to Holocene.

FIGURE 12-46 101 PHYLUM ECHINODERMATA

Starfish, sea urchins, sand dollars, crinoids, blastoids, and others

Name: Echinodermata means "spiny" (echinos) + "skin" (derma). FIGURE 12-47 Representative living echinoderms. 102 PHYLUM ECHINODERMATA

Chief characteristics: Calcite skeleton with five-part symmetry, superimposed on primitive bilateral symmetry.

Echinoderms have a water vascular system with water in a system of tubes within the body.

Tube feet are soft, movable parts of the water vascular system which project from the body and are used in locomotion, feeding, respiration, and sensory perception. 103 PHYLUM ECHINODERMATA

Geologic range: Cambrian to Holcene. Mode of life: Exclusively marine. Some are attached to the sea floor by a stem with "roots" called holdfasts; others are free-moving bottom dwellers. Similarity of embryos between echinoderms and chordates suggests that they may be derived from a common ancestral form. 104 CLASS CRINOIDEA - CRINOIDS

Crinoids are animals which resemble flowers. They consist of a calyx with arms, atop a stem of calcite disks called columnals. The crinoid is attached to the sea floor by root-like holdfasts. Some living crinoids are swimmers, and not attached. Over 1000 genera are known. FIGURE 12-55 Crinoid in living position on the seafloor. 105 CRINOIDS

Geologic range: Middle Cambrian to Holocene. Especially abundant during Mississippian. 106 CLASS BLASTOIDEA - BLASTOIDS

Blastoids are extinct animals with an armless bud-like calyx on a stem. About 95 genera are known. A common genus is Pentremites. Geologic range: Ordovician to Permian - all extinct. FIGURE 12-52 Some common Paleozoic blastoids. 107 CLASS ASTEROIDEA - STARFISH

Starfish are star-shaped echinoderms with five arms. About 430 genera are known. Geologic range: Ordovician to Holocene. FIGURE 12-48 Partially dissected starfish showing elements of the water vascular system and other organs. 108 CLASS OPHIUROIDEA – BRITTLE STARS

Brittle stars have 5 arms, like starfish, but the arms are thin and serpent-like. About 325 genera are known. Geologic range: Ordovician to Holocene. FIGURE 12-47 Representative living echinoderms. 109 CLASS ECHNINODEA

Sand dollars and sea urchins Echinoids are disk-shaped, biscuit-shaped, or globular. Viewed from above, they may be circular or somewhat irregular in shape, but with a five-part symmetry. About 765 genera are known. Geologic range: Ordovician to Holocene. 110 CLASS HOLOTHUROIDEA

Sea cucumbers Soft-bodied echinoderms resembling cucumbers. They have microscopic hard parts called sclerites in various shapes resembling hooks, wheels and anchors. About 200 genera are known. Geologic range: Middle Cambrian?; Middle Ordovician to Holocene 111 CLASS EDRIOASTEROIDEA

Edrioasteroids A group that was probably ancestral to starfish and sea urchins. Globular, discoidal, or cylindrical tests (shells), many of which had concave surfaces. Geologic range: Early Cambrian to Middle Pennsylvanian. 112 CLASS CYSTOIDEA

Cystoids This primitive group had a calyx attached to the seafloor by a stem (like crinoids and blastoids). Distinctive patterns of pores on the plates of the calyx. Geologic range: Cambrian to Late Devonian. Most common during Ordovician and Silurian. 113 THE ECHINODERM-BACKBONE CONNECTION

Echinoderms are closely related to chordates (the group that includes the vertebrates).

The early cell division, embryonic development, and larvae of echinoderms resemble those of chordates, and are different from those of other invertebrates.

Biochemistry of echinoderms is also similar to that of chordates (chemical similarities associated with muscle activity and chemistry of oxygen-carrying pigments in the blood). 114 GRAPTOLITES

Chief characteristics: Organic (chitinous) skeletons consisting of rows or lines of small tubes or cups, called thecae. Tubes or cups branch off a main cord or tube called a stem or stipe. Stipes may consist of one, two, or many branches. Entire colony called a rhabdosome. A filament at the lower end of the rhabdosome is called a nema. 115 GRAPTOLITES

Most graptolites are found flattened and carbonized in black shales and mudstones. Geologic range: Cambrian to Mississippian. (Most abundant during Ordovician and Silurian.) Some living organisms which may be surviving descendants (living fossils) have been recovered in 1989 in the South Pacific and later in Bermuda. Mode of Life: Planktonic (colonies attached to floats).

• FIGURE 12-94 Five major mass extinction episodes. Source: After J. J. Sepkowski Jr., 1994, Geotimes,39(3): 15–17. FIGURE 12-2 Geologic time scale across the Proterozoic–Cambrian boundary. Source:

• FIGURE 12-1 Tiny shell-bearing fossils from the Late Precambrian and Early Cambrian in Siberia. Source: Matthews, C., and Missarzhevsky, V., 1975, Small shelly fossils of late Precambrian and Early Cambrian age. Journal of the Geol. Society of London, 131:289-304. • FIGURE 12-5 The Burgess Shale fauna. Source: • FIGURE 12-13 Reconstruction of Pikaia, the earliest known member of our own phylum, Chordata. Source: • FIGURE 12-8 Anomalocaris, “invertebrate equivalent of the dinosaurs.” Source: • FIGURE 12-10 Marrella, the most elegant and common arthropod in the Burgess Shale fauna. Source: • FIGURE 12-11 The early Cambrian Burgess Shale fossil Hallucigenia. Source: • FIGURE 12-17 Archaeocyathid skeleton. Source: • FIGURE 12-18 Early Paleozoic sponges. Source: • FIGURE 12-23 Common cnidarians. Source: • FIGURE 12-24 Medusaandpolypformsin cnidarians. Source: • FIGURE 12-28 Dwelling positions of articulate and inarticulate brachiopods. Source: • FIGURE 12-35 The monoplacophoran Pilina. Source: • FIGURE 12-34 A common placophoran, the Atlantic Coast chiton. Source: • FIGURE 12-36 Paleozoic bivalves. Source: • FIGURE 12-39 Cephalopod suture patterns. Source: • FIGURE 12-42 Trilobites. Source: • FIGURE 12-46 Mischoptera, a Pennsylvanian-age dragonfly. Source: • FIGURE 12-47 Representative living echinoderms. Source: • FIGURE 12-55 Crinoid in living position on the seafloor. Source: • FIGURE 12-52 Some common Paleozoic blastoids. Source: • FIGURE 12-48 (A) Partially dissected starfish showing elements of the water vascular system and other organs. Source:

PHYLUM CHORDATA Vertebrates, sea squirts or tunicates, lancelets such as Amphioxus. Name: "Chord" means "string," referring to the nerve cord and/or notochord. Geologic range: Cambrian to Holocene. Mode of life: Varied. Among the vertebrates alone, various members are land dwellers, swimmers, or fliers. Paleozoic vertebrates were initially in the sea, but later colonized freshwater and land.

1 Chief characteristics (some are embryonic): 1.Bilateral symmetry. 2.Gill slits. These slits are a series of openings that connect the inside of the throat to the outside of the "neck." 3.Dorsal nerve cord (sometimes called a spinal cord). The nerve cord runs down the "back," connecting the brain with the muscles and other organs. PHYLUM CHORDATA 2 PHYLUM CHORDATA 4.Notochord. A stiff cartilaginous rod which supports the nerve cord.

5.Post-anal tail. This is an extension of the body past the anal opening. 6.Blood that circulates forward in a main ventral vessel and backward in a dorsal vessel.

3 PHYLUM CHORDATA SUBPHYLUM UROCHORDATA Primitive chordates: Sea squirts, ascidians, or tunicates. Larval forms have notochord in tail region.

Chief characteristics: Adults have sac-like bodies, ranging in size from less than 1 mm to a few cm. Larval form resembles a tadpole and has a notochord, dorsal tubular nerve cord, gill slits, and post-anal tail.

4 PHYLUM CHORDATA SUBPHYLUM UROCHORDATA Geologic range: not known

Mode of life: Inhabit overhangs or shaded areas in the low intertidal and subtidal zone. Most live attached as adults. Filter feeders. Behavior resembles that of a sponge. Body contracts abruptly expelling water, giving them the name "sea squirts."

5 PHYLUM CHORDATA SUBPHYLUM CEPHALOCHORDATA

Primitive chordates. Lancelets, Amphioxus, Branchiostoma. Small marine animals with fish-like bodies and notochord. Geologic range: Cambrian to Holocene. Mode of life: Bottom dwellers. Lancelets spend much of their time burrowing in the sand in warm, coastal, marine environments. Filter feeders. Relatively sessile but capable of swimming. Significance: An ancestor to the vertebrates resembled a lancelet-like creature (Pikaia).

6 Chief characteristics: Lancelets resemble a small, colorless anchovy fillet. No obvious eyes or lateral fins. Worm-like. Has segmented axial muscles, gill slits, a dorsal hollow nerve cord, a notochord, and a post-anal tail. No solid skeleton. Nothing resembling a vertebral column. PHYLUM CHORDATA SUBPHYLUM CEPHALOCHORDATA 7 FIGURE 12-60 Branchiostoma, a fishlike member of the subphylum Cephalochordata. WHAT ARE CONODONTS?

The conodonts were previously placed in a separate phylum (Phylum Conodonta), because their affinities were unknown. The current interpretation places the conodont-bearing animal with the Chordates in Phylum Chordata. The organism from which they came is not known with certainty.

Examples of various shapes of conodont elements. Photographs courtesy of K. Chauff 8 CONODONTS Chief characteristics: Microscopic in size Composed of calcium fluorapatite. Shape - cone-shaped teeth, or bars with rows of tooth-like denticles, or irregular knobby plates called platforms. Each conodont element is part of a larger organism. Most fossil occurrences are of disassociated elements, but occasionally they are found arranged in specific assemblages or “apparatuses." 9 CONODONTS Name: Conodont means "cone" + "teeth" (dont) Geologic range: Neoproterozoic to Late Triassic.

Mode of life: Marine, free-swimming. 10

CONODONTS Significance: Useful in biostratigraphy Useful in marine paleoenvironmental interpretation Their color is a good indicator of the temperature to which the rock has been subjected. (This is important in determining whether oil or gas may be present in the rock). 11 WHAT WAS THE CONODONT ANIMAL? Several fossils of conodont animals have been reported, but most were discredited and reinterpreted as an organism which had actually eaten the conodont animal, because the conodont elements were only in the stomach or digestive tract. 12 WHAT WAS THE CONODONT ANIMAL? Sketch of a conodont animal published in 1993 from Lower Carboniferous of Scotland. The conodont animal is found as soft-bodied impressions. The animals lack skeletal parts except for the conodonts, which occur in the mouth region. Photograph courtesy of K. Chauff 13 WHAT WAS THE CONODONT ANIMAL? A fossil discovered (1995) in Ordovician Soom Shale of South Africa contains soft bodied remains of an animal with an elongated eel-like body. The animal had an eye, and had V-shaped musculature along the sides of the body, as in the amphioxus or lancelet.

The organism has a longitudinal band which may mark the position of the notochord.

14 WHAT WERE THE CONODONT ELEMENTS USED FOR IN THE CONODONT ANIMAL? Internal laminated structures within conodont elements indicate that new lamellae were added on the outer surface of many elements, suggesting that they were an internal skeletal appatatus, covered with tissue, rather than being used as teeth.

They may have been supports for a food-gathering apparatus.

Some conodonts show evidence of having been broken and subsequently repaired.

The function of the conodont apparatus is not known. 15 PHYLUM CHORDATA SUBPHYLUM VERTEBRATA The vertebrates are animals with: Segmented backbone consisting of vertebrae Definite head with a skull that encloses a brain Ventrally-located heart Well-developed sense organs Notochord is supplemented or replaced by cartilaginous or bony vertebrae. Arches of the vertebrae encircle and protect a hollow spinal cord.

16 PHYLUM CHORDATA SUBPHYLUM VERTEBRATA Mode of Life: Includes both water-dwelling and land-dwelling tetrapods (from the Latin, meaning four feet). Some walk on four legs and some walk only on the hind legs (bipedal). In some, forelimbs are modified into wings. In some, the limbs have been modified into flippers. Geologic range: Cambrian to Holocene. 17 PHYLUM CHORDATA SUBPHYLUM VERTEBRATA Two major groups of vertebrates: Non-amniotic vertebrates - Egg lacks a covering and must be fertilized externally. Must be wet or in water to reproduce. Amniotic vertebrates - Amniotes. Internal fertilization and an amniotic egg (enclosed egg). Water is not required for reproduction.

18 AMNIOTIC EGG Amnion (or amniotic membrane) encloses the embryo in water (amniotic fluid). Allantois is a reservoir for waste and provides for gas diffusion. It becomes the urinary bladder in the adult. Chorion provides a protective membrane around the egg. Yolk is a storage area for fats, proteins, and other nutrients - food for the embryo. 19 FIGURE 12-59 Amniotic egg. SIGNIFICANCE OF THE AMNIOTIC EGG Provided freedom from dependency on water bodies.

Helped the vertebrates live in diverse types of terrestrial environments.

An important milestone in the evolution of vertebrates.

20 THE FISHES There are five classes of fishes. 1.Agnathids or jawless fish 2.Acanthodians or spiny fish with jaws. Extinct. 3.Placoderms or plate skinned fish with jaws. Extinct. 4.Chondrichthyes or fish with cartilaginous skeletons, including sharks, rays, and skates. 5.Osteichthyes or bony fishes. Most modern fish. Led to evolution of tetrapods.

21 GEOLOGIC RANGES OF THE FIVE CLASSES OF FISHES 22 FIGURE 12-61 Evolution of the five major categories of fishes. CLASS AGNATHA Jawless fishes, including the living lampreys and hagfishes as well as extinct ostracoderms Name: "A-" means "without," and "gnatha" means "jaws." Chief characteristics: Fish without jaws. Mode of life: Swimmers.

23 CLASS AGNATHA Geologic range: Cambrian to Holocene. Ostracoderms were Ordovician to Devonian. Jawless fishes are present in the Harding Sandstone (Lower Ordovician) of Colorado. Also found in Lower Ordovician rocks in Australia and Bolivia. Includes Astraspis.

FIGURE 12-62 Ordovician agnathan Astraspis, from Harding Sandstone, Colorado. 24 OSTRACODERMS

A group of armored jawless fishes called the ostracoderms (name means "shell skin") lived during Early Paleozoic. Ostracoderms were mainly small, sluggish fish that were filter feeders or "mud strainers."

25 FIGURE 12-63 Early Paleozoic ostracoderms. OSTRACODERMS The armor was made of bony material, and served as protection from predators or for storing seasonally available phosphorous.

Bone is made of apatite, which contains phosphorous.

26 EVOLUTION OF JAWS

The first fish with jaws appeared in nonmarine rocks during Late Silurian.

The evolution of the jaw expanded the adaptive range of vertebrates.

Used for biting and grasping.

Led to more varied and active ways of life, and to new sources of food.

27 EVOLUTION OF JAWS Origin of jaws - two hypotheses: Modification of a front pair of bone or cartilage gill supports. More recent hypothesis: Modification of the velum, a structure used in respiration and feeding in lamprey larvae.

Both hypotheses are based on anatomy and embryology of living fishes.

28 CLASS ACANTHODII

Acanthodians or spiny fishes. The first fishes to have jaws. Name: "Acanthos" means "spiny." Chief characteristics: Primitive spiny fishes with jaws. Geologic range: Late Silurian to Permian. Most numerous during Devonian. Extinct. Mode of life: Swimmers. Nonmarine.

29 FIGURE 12-64 Early Devonian acanthodian fish Climatius. CLASS PLACODERMI

Placoderms or "plate-skinned" fishes. Name: "Placo-" means plate and "derm" means "skin." Chief characteristics: Fish with jaws and armor plating. Geologic range: Late Silurian to Late Devonian. Extinct. Mode of life: Swimmers. Some were large carnivorous predators, such as Dunkleosteus, which grew to about 9 m long Dunkleosteus (top) J. Sibbick, (bottom) Courtesy of the U.S. National Museum of Natural History, Smithsonian Institution; photograph by Chip Clark) 30

CLASS CHONDRICHTHYES - SHARKS

Sharks, rays, and skates Name: From "chondros," meaning "cartilage," and "icthyes" meaning "fish." Chief characteristics: Cartilaginous fishes. Skeleton made of cartilage not bone. Rarely preserved. Geologic range: Middle Paleozoic (Late Silurian or Devonian) to Holocene. Mode of life: Swimmers. Marine, except one Late Carboniferous freshwater genus. The genus Cladoselache, is found in Devonian shales on the southern shore of Lake Erie. 31 CLASS OSTEICHTHYES - BONY FISHES

Bony fishes Name: "Osteo" means "bone" and "ichthyes" means "fish." Chief characteristics: Skeleton of bone, not cartilage. Modern bony fishes are of this type. Geologic range: Devonian to Holocene. Mode of life: Swimmers. Marine and freshwater. The earliest lived in freshwater. The most numerous, varied, and successful of all aquatic vertebrates. 32 FIGURE 12-68 CLASS OSTEICHTHYES - BONY FISHES

Bony fishes played a key role in the evolution of tetrapods (four-legged animals).

Two types of bony fish are significant: Subclass Actinopterygii - the ray-finned fish. Subclass Sarcopterygii - the lobe-finned fish or lungfish. 33 SUBCLASS ACTINOPTERYGII

Ray-finned fish Dominant fishes in the world today. No muscular base to the paired fins. Fins are thin structures supported by radiating rods or rays. First appeared during Devonian freshwater lakes and streams, and then expanded their geographic range to the sea.

34 SUBCLASS SARCOPTERYGII - LOBE-FINNED FISH OR LUNGFISHChief Characteristics: Leg-like fins: Muscular fins used to "walk" on pond or stream bottoms. Lungs: A pair of openings in the roof of the mouth led to nostrils. Able to rise to the surface and breathe air with lungs when the water became foul or stagnant. Some had both lungs and gills. 35 SUBCLASS SARCOPTERYGII – LOBE-FINNED FISH OR LUNGFISH

Geologic range: Late Devonian to Holocene

Significance: This group gave rise to the amphibians and other tetrapods (four-legged animals). Types of sarcopterygians: Order Dipnoi or dipnoans Order Crossopterygii or crossopterygians – the ancestor of the amphibians

36 ORDER DIPNOI - DIPNOANS

Chief characteristics: They can breathe with lungs during the dry season, and can burrow into the mud during droughts. Name: Dipnoi means "double breather" Significance: This group did not lead to tetrapods, but includes interesting freshwater lungfish living today in Australia, Africa and South America. FIGURE 12-69 Dipterus, a Devonian lungfish. 37 ORDER CROSSOPTERYGII - CROSSOPTERYGIANS

Chief characteristics: Short, muscular, paired fins. Had a single limb bone called the humerus, followed by the radius and ulna in front fins, and the tibia and fibula in hind fins. The adaptation assisted movement in shallow water, and allowed the fish to move from a stagnant or drying body of water, to another body of water. 38 ORDER CROSSOPTERYGII - CROSSOPTERYGIANS

Significance: Considered to be ancestral to the amphibians because of the arrangement of bones in their fins, the pattern of bones of the skull, and the structure of their teeth. 39 TYPES OF CROSSOPTERYGIAN FISH

1.Rhipidistians - This group led to the amphibians 2.Coelacanths - Lobe-finned crossopterygian fish invaded the sea and gave rise to coelacanths. Coelacanths were long-believed to be extinct and are considered to be living fossils. One was caught in 1938 near Madagascar. More have been caught since. Latimeria, a modern coelacanth. Tail is similar to that of Dipterus, but very different from that of ray-finned fish. 40 FIGURE 12-75 SIMILARITIES BETWEEN CROSSOPTERYGIAN FISH AND AMPHIBIANS

1.The same limb bones are present. Early amphibian (left). Crossopterygian fish (right). The major limb bones are coded r, u and h. r = radius u = ulna h = humurus 41 FIGURE 12-72 SIMILARITIES BETWEEN CROSSOPTERYGIAN FISH AND AMPHIBIANS

2.The same skull bones are present. Devonian amphibian, Ichthyostega (right). Crossopterygian fish (left) 42 FIGURE 12-73 THE ADVENT OF TETRAPODS

Tens of millions of generations passed before crossopterygian fish evolved into animals that could live entirely on land. The early tetrapods (four-legged animals) continued to return to water to lay their fish-like, naked eggs. Fish-like tadpoles hatched from these eggs, which used gills for respiration. 43 ANATOMICAL CHANGES ASSOCIATED WITH THE SHIFT FROM WATER TO LAND:

1.Three-chambered heart developed and functioned to pump blood more efficiently to the lungs 2.Limb and girdle bones altered to support the body above the ground 3.Spinal column changed to become sturdy but flexible 4.Fish spiracle (vestigial gill slit) became amphibian eustachian tube and middle ear 44 ANATOMICAL CHANGES ASSOCIATED WITH THE SHIFT FROM WATER TO LAND:

5.Bones of the ear changed to function better in air than in water (modification of hyomandibular bone that propped fish braincase and upper jaw together, into an ear ossicle called the stapes) 6.Eardrum (tympanic membrane) formed across a notch in the skull 45 AMPHIBIANS ARE INTERPRETED TO BE DESCENDED FROM CROSSOPTERYGIAN FISHES BECAUSE OF:

1.Arrangement of bones in amphibian limbs compared with the fins of crossopterygian fish 2.Pattern of bones of the skull 3.Structure of the teeth - highly infolded like a maze (or labyrinth), and called labyrinthodont teeth. 4.Bones of the spinal column in early forms. 46 CLASS AMPHIBIA – THE AMPHIBIANS

Name: "Amphi" means "both" or "double," and "bios" means "life." "Amphibios" means living a double life, referring to living in water and on the land.

Chief characteristics and mode of life: Amphibians can live on the land as adults, but they lay their eggs in water. Young amphibians live in the water and are fish-like (tadpoles). 47 THE AMPHIBIANS

Geologic range: Late Devonian to Holocene.

For 50 million years, from Late Devonian to Middle Carboniferous, amphibians were the only vertebrates to the inhabit the land. Some adult amphibians reverted to an aquatic mode of life, while others retained a terrestrial lifestyle. 48 FIGURE 12-77 Evolution of lobe-fin fishes and amphibians from Devonian fishes. ICHTHYOSTEGA – THE FIRST AMPHIBIAN

The first terrestrial vertebrate, Ichthyostega, appeared in Late Devonian, about 375 m.y. ago Found in freshwater deposits. "Ichthyo" means "fish" and "stega" means "roof" or "cover" (probably referring to the bones in the roof of the skull). 49 FIGURE 12-78 ICHTHYOSTEGA – THE FIRST AMPHIBIAN

Ichthyostega retained many features of its fish ancestors, such as: Similar skull structure, including arrangement of nostrils Loosely connected fish-like spinal column It also had a number of unique traits such as: Five-toed limbs Pelvic and pectoral girdles, allowing it to walk on land 50

Amphibians inhabited the Carboniferous coal swamps, and were abundant and varied.

They had several different modes of life, including some with an aquatic lifestyle (as suggested by features such as a flattened body and skull, reduced limbs, and a slender snake-like body), and some that were clearly land dwellers (with stout limbs, short body and tail). THE AMPHIBIANS 51

Some Carboniferous amphibians were quite large, ranging up to 20 feet (about 6-7 m) long. In contrast, most living amphibians are small.

Cacops, a small Early Permian labrynthodontic amphibian. THE AMPHIBIANS 52 CLASS REPTILIA - THE REPTILES

Name: From "reptilis" meaning "creeping.“

Chief characteristics: Skull characteristics that distinguish reptiles from amphibians: Reptile skull is high and narrow, compared with the low, broad amphibian skull. In reptiles, the roof of the mouth is arched, with small openings. In amphibians, it is flat with large openings. 53 CLASS REPTILIA - THE REPTILES Mode of life: Complete colonization of land was achieved by the reptiles, which can lay their eggs on dry land.

Geologic range: Pennsylvanian to Holocene.

The oldest reptile fossils, genus Hylonomus, (300 m.y. old) are found in Nova Scotia inside fossilized hollow trees filled with sediment. These reptiles were about 24 cm (1 ft) long. They resemble modern insect-eating lizards. 54 CLASS SYNAPSIDA - THE SYNAPSIDS

The synapsids had diverged from the reptiles by Late Carboniferous.

The synapsids were long considered to be a subclass of reptile, but more recent cladistic analysis shows that they diverged from ancestors completely different than Hylonomus and other true reptiles. 55 THE SYNAPSIDS The synapsids were the dominant terrestrial vertebrates during Permian. This group was formerly called the "mammal-like reptiles," however the name has been abandoned because they are not really reptiles. Synapsids include the pelycosaurs and the therapsids. 56 PELYCOSAURS

Several species of pelycosaurs had fins or "sails" on their backs, supported by rod-like extensions of their vertebrae. These sails may have been used as temperature regulating mechanisms. Pelycosaurs lived during Carboniferous and Permian. Sail-backed forms are Permian. Permian pelycosaur, Dimetrodon. 57 PELYCOSAURS

Two well known pelycosaurs, which evolved their sails independently were the carnivorous Dimetrodon, and the plant-eating Edaphosaurus. Dimetrodon has a larger skull and teeth than does Edaphosaurus, suggesting that Dimetrodon was a meat-eater. 58 THERAPSIDS Therapsids were small to moderate-sized animals with mammalian skeletal characteristics: 1.Fewer bones in the skull than the other reptiles 2.Mammal-like structure of the jaw 3.Differentiated teeth (incisors, canines, and cheek teeth) 4.Limbs in more direct alignment beneath the body 5.Reduction of ribs in the neck and lumbar regions, allowing greater flexibility 59 THERAPSIDS

6.Double ball-and-socket joint between the skull and neck 7.Bony palate which permitted breathing while chewing (an important characteristic for animals evolving toward mammalian warm-bloodedness). Efficient breathing provides oxygen needed to derive heat energy from food. 8.Whisker pits on the snout.

Geologic range: Permian to Triassic. 60 THERAPSIDS – CYNOGNATHUS

Mammal-like features are well developed in the therapsid, Cynognathus. Name: From "kynos" meaning "dog" and "gnathos" meaning "jaw" or "tooth." 61 THERAPSIDS - CYNOGNATHUS

Examination of the bone on the snout portion of the skull reveals probable "whisker pits," suggesting that they had hair, which may have functioned to insulate the animal and slow the rate of heat loss. 62 PLANTS OF PALEOZOIC 63 STROMATOLITES - A PHOTOSYNTHETIC PLANT ANCESTOR The earliest photosynthetic organisms were in the sea. Stromatolites, built by photosynthetic bacteria (cyanobacteria, sometimes called blue-green algae), were ancestral to Paleozoic plants. They were not plants themselves. 64 STROMATOLITES - A PHOTOSYNTHETIC PLANT ANCESTOR

Stromatolites: Expanded during Proterozoic Are present in Phanerozoic limestones.

Most Precambrian stromatolites grew in shallow marine and intertidal environments, but some lived in freshwater. 65 STROMATOLITES - A PHOTOSYNTHETIC PLANT ANCESTOR Stromatolite reefs were widespread during Cambrian, but declined during Ordovician. They are typically found in areas lacking marine invertebrates, which feed on the cyanobacterial mats.

The appearance of abundant marine invertebrates during Cambrian led to the decline of the stromatolites. Why? They ate them. 66 MARINE ALGAE

The next step in the evolutionary path to land plants was probably the green algae or chlorophytes. Kingdom Protista.

Marine algae fossils are found in some Paleozoic rocks.

Types of marine algae: 1.Chlorophytes 2.Receptaculitids 67 CHLOROPHYTES 1.Chlorophytes - Green algae.

•Cambrian to Holocene.

•A close relationship between chlorophytes and land plants is suggested by the adaptation of some species to freshwater and moist soil. 68 RECEPTACULITIDS

2.Receptaculitids are lower Paleozoic marine fossils resembling sunflowers. Produced by organisms of uncertain affinity. Interpreted as lime-secreting algae. Most are found in Ordovician rocks, but they are also present in some

Silurian and Devonian rocks as well. 69 LAND PLANTS Land plants include: 1.Bryophytes - non-vascular plants Mosses, liverworts, and hornworts.

Devonian to Holocene. 2.Tracheophytes - vascular plants

Trees, ferns, and flowering plants. Silurian to Holocene 70 TRACHEOPHYTES

Tracheophytes have vascular tissues, or an internal system of tubes and vessels, that transport water and nutrients from one part of the plant to another.

A water transport system is important, because plants generally withdraw water from below the ground. Below the ground there is water but no light. Above the ground there is sunlight but there may not be water. The vascular system allows the plant to take advantage of both places. 71 TRACHEOPHYTES The oldest unquestioned vascular plant fossils occur in Silurian rocks. Small, leafless plants with thin branching stems. These plants are called psilophytes. Spore bodies are present on the ends of the stems in fossils of Cooksonia. Cooksonia, an early vascular plant of Late Silurian - Early Devonian. Height about 4 cm. 72 FIGURE 12-85 MAJOR ADVANCES IN LAND PLANTS

Three major advances in land plant history, developing more efficient reproductive systems: 1.Seedless spore-bearing plants, appearing during Ordovician, and flourishing in Carboniferous coal swamps 2.Seed-producing, pollinating, but non-flowering plants appearing during Late Devonian (gymnosperms, such as conifers) 3.Flowering plants, appearing during Late Mesozoic (angiosperms)

73 SPORE-BEARING PLANTS

The first plants to invade the land were spore-bearing plants.

In fact, the first evidence of land plants is the presence of spores in Ordovician rocks. Spores are plant reproductive structures. Familiar spore-bearing plants include mosses and ferns. 74 LIFE CYCLE OF SPORE-BEARING PLANTS

The life cycle of spore-bearing plants differs from that of the more familiar seed-bearing plants.

Alternation of generations between diploid (double set of chromosomes) and haploid (single set of chromosomes) forms.

Water is required for fertilization.

75 THE FIRST SEEDS

Seeds appeared during Late Devonian, although it is not known which plant produced them.

Seed-bearing plants became more abundant during Carboniferous.

The seed is significant because it freed plants from their dependence on moist environments and allowed them to inhabit dry land, much as the amniotic egg freed animals from their dependence on wet environments. 76 INVASION OF THE LAND BY PLANTS

The invasion of the land by plants profoundly altered the landscape. Plant roots slowed erosion. Decaying vegetation led to soil formation. Plants also provided a food source for animals, which invaded the land after the appearance of land plants. Animals could not have survived on land without a food source (plants) in place.

77 EVOLUTION OF WOOD

As plants evolved wood, they were able to withstand the pull of gravity and grow taller. During Middle Devonian, the first wood appeared in plants of the genus Rhynia. Rhynia, a Middle Devonian vascular land plant with woody tissues called xylem. 78 FIGURE 12-87 THE FIRST TREES The first trees were present by Late Devonian.

By Carboniferous, trees reached 30 m tall or more, with trunks 1 m in diameter. 79 CARBONIFEROUS COAL

There are more plant fossils in Carboniferous strata than in any other geologic interval. Plants gave Carboniferous its name, because of the vast coal deposits which formed from plant remains in lowland swamps. Coal is dominated by the element carbon. Coal represents an enormous biomass of plants because it takes several cubic meters of wood to make one cubic meter of coal. 80 COMMON PLANTS OF CARBONIFEROUS 1.Lycopods or Lycopsids - club mosses 2.Sphenopsids - horsetails, scouring rushes 3.Ferns 4.Gymnosperms a.Seed ferns b.Cordaites c.Conifers d.Ginkgoes 81 LYCOPODS OR LYCOPSIDS

Phylum Lycopodophyta or Lycopsida Club mosses, scale trees Spore-bearing plants were confined to swamps because spores require moisture to germinate. Some grew to be 30 m tall and 1 m diameter. Geologic range: Silurian to Holocene. (Only a few species persisted after Permian.) Common genera = Lepidodendron and Sigillaria. 82 SPHENOPSIDS Phylum Equisetaphyta or Sphenopsida Spore-bearing and similar to living horsetails or scouring rushes. Interpreted as living in moist areas or standing water. Geologic range: Devonian to Holocene. (But only a few persisted after Permian.) Common genus = Calamites 83 FERNS

Phylum Polypodiophyta Ferns are vascular plants that reproduce by means of spores. They live in moist habitats. Geologic range: Devonian to Holocene. 84 GYMNOSPERMS Phylum Pinophyta or Gymnospermophyta Conifers, cycads, ginkgoes, and various evergreen plants without flowers The word "gymnosperm" means "naked seed." Seed-bearing plants. No flowers. Seed-bearing plants no longer require moist habitats. This led to the expansion of plants into drier areas. Geologic range: Middle Paleozoic to Holocene.

85 SEED FERNS

Gymnosperms. Class Pteridospermophyta Fernlike leaves, but reproduced with seeds instead of spores. Geologic range: Devonian to Holocene. Common genera = Neuropteris and Glossopteris. One of the best-known is Glossopteris, which lived in Gondwana during Carboniferous and Permian. They were sometimes associated with glacial deposits, suggesting that they were adapted to cool climates. 86 CORDAITES Gymnosperms. Class Pinopsida, Order Cordaitales Seed-bearing gymnosperms with strap-like leaves that were ancestors to the modern conifers. Tall trees (up to 50 m). Abundant in Carboniferous coal swamps. Extinct by the end Permian. 87 CONIFERS

Gymnosperms. Class Pinopsida, Order Coniferales The word "conifer" means "cone bearing." Trees with cones which contain seeds. Today conifers are represented by trees such as pines, cedars, hemlocks, spruces, firs, etc. Conifers spread widely during Permian, perhaps as a result of the drier conditions which led to the demise of the coal swamps. 88 GINKGOES Gymnosperms. Class Ginkgopsida Deciduous trees (they drop their leaves) Fan-shaped leaves. They produce a fleshy fruit but have no flowers. Geologic range: Early Permian to Holocene. Maximum diversity during Jurassic. Represented by a single species today, Ginkgo biloba. It is extinct in the wild, but is widely grown as an ornamental tree. 89 MASS EXTINCTIONS OF PALEOZOIC

Paleozoic was a time of adaptive radiations and extinctions.

Many of the geologic periods of Paleozoic began with adaptive radiations, or times of rapid evolution of organisms. Several of the Paleozoic periods ended with extinction events of varying severity. 90 MASS EXTINCTIONS OF PALEOZOIC The three most catastrophic extinctions during Paleozoic Era were at the following times: End of Ordovician (443 m.y. ago) End of Devonian (359 m.y. ago)

End of Permian (251 m.y. ago)

Permian extinction was the most severe. The extinction at the end Permian is considered to be the most catastrophic mass extinction in the history of life. 91 Diversity of marine animals, and extinction events over geologic time. MASS EXTINCTIONS OF PALEOZOIC 92 LATE ORDOVICIAN EXTINCTIONS Following a slight dip in diversity at the end Cambrian, Ordovician was a time of renewed diversification. The number of genera increased rapidly, and the number of families increased from about 160 to 530. This increase was particularly dramatic among trilobites, brachiopods, bivalved molluscs, and gastropods.

An extinction event at the end of Ordovician led to an abrupt decline in diversity. 93 LATE ORDOVICIAN EXTINCTIONS

The extinction occurred in two phases.

First phase - affected planktonic and nektonic (floating and swimming) organisms such as graptolites, acritarchs, many nautiloids and conodonts, as well as benthic (bottom-dwelling) organisms such as trilobites, bryozoa, corals, and brachiopods. Second phase - affected several trilobite groups, corals, conodonts, and bryozoans. 94 LATE ORDOVICIAN EXTINCTIONS Both phases of the extinction event were related to global cooling and the growth of glaciers in Gondwana. Glaciation was coupled with the lowering of sea level and a reduction in shallow water habitat. As the climate cooled, tropical organisms showed the greatest decline. As warming occurred and the glaciers began to melt, organisms which were adapted to the cooler conditions began to suffer extinction. This was the second phase of extinctions. 95 LATE DEVONIAN EXTINCTIONS Late Devonian extinctions occurred over a span of about 20 million years, and appear to have been the result of an ecological crisis in the seas, perhaps induced by changes occurring on the land. 96 LATE DEVONIAN EXTINCTIONS Devonian saw the appearance of trees and spread of land plants. This would have accelerated weathering rates, leading to large volumes of nutrients being washed into the seas. Large quantities of nutrients in the water (such as phosphorus) causes algal blooms. Bacteria breaking down large quantities of dead algae uses up all of the oxygen in the water, causing anoxic conditions (= "without oxygen"). This process is called eutrophication, and it occurs today in lakes, and causes massive "fish kills."

97 LATE DEVONIAN EXTINCTIONS

Extensive Devonian black shale deposits (for example, the Chattanooga Shale) suggest the widespread occurrence of anoxic conditions in the Devonian sea. Glaciation may have been an additional contributing factor. By Late Devonian, South America had drifted over the South Pole, and glaciations occurred. Overall, 70% of marine invertebrate families went extinct during Late Devonian. 98 LATE DEVONIAN EXTINCTIONS Organisms most strongly affected (but not totally wiped out) by the Devonian extinction were: Tabulate corals Rugose corals Stromatoporoids Brachiopods Goniatite ammonoids (cephalopod molluscs) Trilobites Conodonts Placoderm fish 99 LATE PERMIAN EXTINCTIONS Late Permian is marked by a catastrophic extinction event which resulted in the total disappearance of many animal groups.

This was the largest extinction event in the history of life, exceeding even the extinction event at the end of Cretaceous, which killed the dinosaurs. 100 LATE PERMIAN EXTINCTIONS More than 90% of all marine species that existed during Permian disappeared or were severely reduced in number. Nearly half of the known families disappeared. Tropical forms experienced the most extensive losses. 101 LATE PERMIAN EXTINCTIONS

The following marine organisms were extinct by the end Permian: Fusulinid foraminifera Rugose corals Tabulate corals Blastoids Trilobites (which had become extinct somewhat earlier during Permian) 102 LATE PERMIAN EXTINCTIONS Other groups of organisms were severely reduced in diversity, with some surviving species: Brachiopods Crinoids Bryozoa Ammonoids

Organisms which inhabited warm waters shifted their distributions toward the equator. Cool conditions prevented construction of reefs and the formation of limestones. 103 LATE PERMIAN EXTINCTIONS

Permian extinction also affected land dwellers. More than 70% of land animals disappeared or were severely reduced, including: Amphibian families Reptile families Synapsids (once called "mammal-like reptiles") 104 LATE PERMIAN EXTINCTIONS Among the plants, the spore-bearing plants that inhabited tropical coal swamps were replaced by seed-bearing gymnosperms, that could inhabit cooler, drier climatic conditions. 105 CONTRIBUTING FACTORS Many factors may have contributed to the Permian mass extinction: 1.Climatic change associated with assembly of Pangea – Global cooling and drying, along with interruption of equatorial circulation 2.Glaciation at both north and south ends of Pangea 3.Reduction in epicontinental seas as sea level dropped (habitat loss) 106 CONTRIBUTING FACTORS 4.Unusually active volcanism releasing CO2 (flood basalts in Siberia), leading to global warming, which may have triggered release of large stores of methane gas frozen in sediments on the sea floor, causing increased global warming. 5.Possibility of an extraterrestrial impact, as indicated by spherical carbon molecules containing an extraterrestrial helium-3 isotope 107 Diversity of marine animals, and extinction events over geologic time. 108 109

• FIGURE 12-60 Branchiostoma, a fishlike member of the subphylum Cephalochordata. Source: • FIGURE 12-59 Amniotic egg. Source: • FIGURE 12-61 Evolution of the five major categories of fishes. Source: After Romer, A., 1945, Vertebrate Paleontology, Chicago: University of Chicago Press. • FIGURE 12-62 Ordovician agnathan Astraspis, from Harding Sandstone, Colorado. Source: Elliot, D., 1987, A reassessment of Astraspis desiderata, the oldest North American vertebrate. Science. 237:190-192. • FIGURE 12-63 Early Paleozoic ostracoderms. Source: • FIGURE 12-64 Early Devonian acanthodian fish Climatius. Source: Romer, A., 1945, Vertebrate Paleontology, Chicago: University of Chicago Press. • FIGURE 12-68 Cheirolepis, the ancestral bony fish that lived during the Devonian Period. Source: • FIGURE 12-69 Dipterus, a Devonian lungfish. Source: • FIGURE 12-75 Latimeria, a surviving coelacanth in the ocean near Madagascar. Source:

• FIGURE 12-72 Limb bones of an early amphibian (left) and crossopterygian fish (right). Source: • FIGURE 12-73 Skulls and lower jaws of a Eusthenopteron (left) and Devonian amphibian Ichthyostega (right). Source: • FIGURE 12-77 Evolution of lobe-fin fishes and amphibians from Devonian fishes. Source: Colbert, E. and Morales, M., 1991, Evolution of Vertebrates, 4th edition.This material is reproduced with permission of John Wiley & Sons, Inc. • FIGURE 12-78 The Ichthyostega skeleton retains the fishlike form of its crossopterygian ancestors. Source: • FIGURE 12-85 Late Silurian/Early Devonian vascular plant, Cooksonia. Source: • FIGURE 12-87 Middle Devonian vascular land plant, Rhynia. Xylem. Source: