Review, 1st Paleozoic Vertebrate lecture

• At one point in their lives, all chordates have:– Notochord– Dorsal hollow nerve cord– Gill/phyrangeal slits– Tail

• First vertebrates were marine fish without jaws– Ostracoderms

• Devonian = Age of Fish

Evolution in the Devonian

• Evolution of jaws was a big deal– Extended ecological web/opened new

ecological niches

• Ray Finned Fish and Lobe Finned fish– Lobe fins -> lungfish, crossopterigians (both

have protolungs)– Crossopterygians -> amphibians

• First creatures on land were Arthropods (early Devonian)

• Although amphibians were the first vertebrates to live on land, they were not the first land-living organisms

• Land plants, which probably evolved from green algae, first evolved during the Ordovician

• Furthermore, insects, millipedes, spiders, and snails invaded the land before amphibians

Amphibians—Vertebrates Invade the

Land

• The oldest amphibian fossils Ichthyostega– found in the Devonian of eastern Greenland– streamlined bodies, long tails, and fins– four legs, a strong backbone, a rib cage, and

pelvic and pectoral girdle

Precursor organism (Acanthostega)Was adapted to movement in Wet boggy environments

Oldest Amphibians

• Like other groups that moved into previously unoccupied niches – amphibians underwent rapid adaptive radiation – became abundant during the Carboniferous and Early Permian

• Little resemblance to modern amphibians

• Much more diverse

Rapid Adaptive Radiation

• Reconstruction of a Carboniferous coal swamp

Carboniferous Coal Swamp

Large labyrinthodont amphibian Eryops

The serpentlike Dolichosoma

• In passing from water to land, plants and animals had to solve the same basic problem

– the method of reproduction was the major barrier to expansion into the various terrestrial environments

– required evolution of the seed in plants and the amniote egg in animals

Transition from Water to Land

• Amphibians limited in colonizing the land – had to return to water to lay their gelatinous eggs

• Evolution of the amniote egg freed reptiles from this constraint

Evolution of the Reptiles —

the Land is Conquered

http://www.geoclassics.com/mesosour.htm

• In an amniote egg – the embryo is

surrounded by a liquid sac, the amnion cavity

– provided with a food source (yolk sac) and waste sac

• Its evolution freed reptiles to inhabit all parts of the land

Amniote Egg

• In this way the emerging reptile is – in essence a miniature adult– bypassing the need for a larval stage in the water

• The evolution of the amniote egg allowed vertebrates – to colonize all parts of the land – no longer had to return to the water as part of their

reproductive cycle

Able to Colonize All Parts of the Land

• Reconstruction and skeleton of Hylonomus lyelli from the Pennsylvanian Period

One of the Oldest Known Reptiles

– Hylonomus lyelli was about 30 cm long

• Evolutionary relationship among the Paleozoic reptiles

Paleozoic Reptile Evolution

• Most pelycosaurs have a characteristic sail on their back• Sail explanations: display, thermoregulation• Odd: not closely related; neither had ‘sailed’ predecessor• Adaptive escalation?

Pelycosaurs (Finback Reptiles)

The carnivore Dimetrodon

The herbivore Edaphosaurus

• The pelycosaurs became extinct during the Permian – and were succeeded by the therapsids – that evolved from the carnivorous pelycosaur lineage – and rapidly diversified into

• herbivorous • and carnivorous lineages

Therapsids—Mammal-like Reptiles

• A Late Permian scene in southern Africa showing various therapsids

Therapsids

Dicynodon

Moschops

– Many paleontologists think therapsids were endothermic– and may have had a covering of fur

• Therapsids were small- to medium-sized animals – displaying the beginnings of many mammalian features

• Many paleontologists think therapsids were endothermic

• or warm-blooded – enabling them to maintain a constant internal body

temperature– allowing them to expand into a variety of habitats

Therapsid Characteristics

How are we related to them anyway?

• Relationships among Amniota are tracked via ‘fenestrae’, or openings in the head.

• Fenestrae:– Make the head

lighter– Anchor points for

muscles

Fenestrae in the descendents of proterothyrids

• Fish– First appeared in the Cambrian (jawless fish – first vertebrate)– Diversified in Devonian (Age of Fish)

• Amphibians– First appeared in the Devonian– Evolved from lobe-finned fish

• Reptiles– First appeared in Pennsylvanian– Did not need to return to water to reproduce

Summary

Plant Evolution

• Evolution of photosynthesis: Archaean cyanobacteria

• Genetic evidence suggests that plants evolved from green algae

• No Cambrian explosion for plants– Many steps needed to move plants

onto the land

Buoyancy and humidity

• How to keep your guts wet in a dry world?– Cutin: exterior plant waxes protect from dessication

• How to stay upright when you’re not buoyant in air?– Cellulose and lignin: rigid polymers that make cells

strong

• How to grow bigger than a few centimeters in a dry world?– Develop the ability to move fluids from soils to

leaves

• Earliest plants did not produce seeds

• The sedimentary rocks in which these plant fossils are found – indicate that they lived in low, wet, marshy, freshwater

environments

Earliest Land Plant

• The earliest known fertile land plant was Cooksonia– seen in this fossil from

the Upper Silurian of South Wales

Vascular plants

– Vascular system:• network of tubes which distribute nutrients and

remove wastes• Not clear if Cooksonia was truly vascular• First definitive vascular plant: ferns

• Major events in the evolution of land plants– The Devonian Period was a time of rapid evolution for the land

plants

Plant Evolution

– the appearance of leaves

– and emergence of seeds

Early Devonian Plants• Reconstruction of an Early Devonian landscape

Dawsonites

Protolepidodendron

Bucheria

– showing some of the earliest land plants

• Early Devonian – relatively small – low-growing

– bog-dwelling types of plants

• Late Devonian – tree-size plants up to 10 m

tall

Early and Late Devonian Plants

Chaleuria cirrosa

• The evolution of the seed during the Late Devonian – liberated land plants from their dependence on moist

conditions – and allowed them to spread over all parts of the land

• In the seed method of reproduction– the spores are not released to the environment

– but are retained on the spore-bearing plant

– where they grow into the male and female forms

Evolution of Seeds

• In the case of the gymnosperms • or flowerless seed plants

– male cone produces pollen – egg is contained in the female cone– After fertilization

• seed develops into a mature, cone-bearing plant

• Seed plants • like reptiles

– were no longer restricted to wet areas – but were free to migrate into previously unoccupied dry

environments

Gymnosperms

• Rocks of the Pennsylvanian Period are the major source of the world's coal

• The geologic and geographic conditions of the Pennsylvanian – ideal for the growth of seedless vascular plants – these coal swamps had a very diverse flora

Late Carboniferous and Permian Floras

• Reconstruction of a Pennsylvanian coal swamp with its characteristic vegetation

Pennsylvanian Coal Swamp

• An important non-swamp dweller was Glossopteris, the famous plant so abundant in Gondwana (a seed fern)– Great resource for paleobiogeographers

Glossopteris

http://www.lowcountrygeologic.com/plants/gloss1.htm