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5/7/2011
1
Paleozoic Life
History
Vertebrates and Plants
Vertebrate Evolution
Chordates – Animals with a notocord, not
necessarily a backbone.
Vertebrates are a subphylum of Chordates
Earliest records of Chordates are without
vertebrae, soft-bodied.
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–a notochord, a dorsal hollow nerve cord, and gill slits
Amphioxus
Oldest Known Chordate
Yunnanozoon lividum 525 million year old rocks of China
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Origin of Vertebrates
Closely related to Echinoderms
Cell Cleavage (see fig. 13.3)
Biochemistry of muscle activity
Blood proteins
Larval stages
Vertebrates acquire a 2nd set of genes?
Fish
Ostracoderms –
earliest (Cambrian and Ordovician)
jawless
shallow marine
Probably bottom feeders
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Ostracoderms
Cambrian to Devonian
Fish evolve jaws
Joints in forward gill arches
Mouth could open wider
Pumped more oxygen past gills
Allowed eating larger prey
Acanthodians – 1st jawed fish
Spiny, scaly, teeth, reduced body armor
Most abundant in the Devonian, extinct in Permian
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Fish with jaws: 1st Acanthodians
Various primitive acanthodians from Early Devonian England and
Scotland, Mesacanthus pusillus, Parexus falcatus, Ishnacanthus
gracilis
Age of Fishes = Devonian
Placoderms
Late Silurian to Permian
Plate-skinned fish – heavy armor
Freshwater and ocean
Bottom dwellers (small) and Large predators
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Dunkleosteus More than 12m in length
Phyllolepis
Coccosteus (top, Middle Devonian), Campbellodus (left, Late Devonian),
and Bothriolepis (bottom right. Late Devonian) ©
Age of Fishes = Devonian
Cartilaginous fish – Chrondrichthyes
Sharks, rays and skates
Early Devonian to recent
White shark
Ray
Skate
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Age of Fishes = Devonian
Bony Fish – Osteichthyes Ray-finned fish: with thin bones radiating in fins
Devonian to Recent
Most common fish today; Mesozoic and Cenozoic
Lobe-finned fish: with thick bones and muscles for fins
Silurian to Recent
Many extinct in Permian
Coelacanth- thought to be extinct in Cretaceous, found in modern seas = Latimeria
Lungfish has modified swim bladder that allows it to breath air
Crossopterigians probably evolved into amphibians
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Transition to Amphibians
Group of Crossopterigians called
rhipidistians appear to be ancestors of
amphibians
Structural similarities are striking
Earlier and earlier finds are causing some
rethinking of timing (Acanthostega)
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Crossopterigian Amphibian
Invasion of the land
Land plants evolve from algae in the late Ordovician (more about this later)
Arthropods (insects, millipedes, spiders, scorpions) and Gastropods (snails) by Devonian
Difficulties to surmount Desiccation
Reproduction
Effects of gravity
Extraction of oxygen from air
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Vertebrates Invade Land
Several transitional species
Acanthostega – many features of amphibians
but not truly land dwelling; shallow fresh water
Panderichthys – transitional, shallow water
Tiktaalik roseae – fish and tetrapod features
Oldest known amphibian, Ichthyostega,
Late Devonian
Acanthostega
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Panderichthys
Ichthyostega – oldest amphibian
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Carboniferous Landscape
Labyrinthodont – Late Paleozoic
Proterogyrinus
Labyrinthodont
tooth cross-section
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Eryops Large labyrinthodont amphibian
Fate of the Amphibians
Many became extinct at Permian/Triassic
extinction event (66%)
Few survived the Cretaceous/Tertiary
event and those are small
Frogs, salamanders etc.
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Reptiles conquer the land
Amphibians must have water in which to
lay gelatinous eggs.
Reptiles have Amniotic Eggs that have
shells and don’t dry out in air.
Reptiles therefore could venture farther
onto the land
Amniote Egg
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Westlothiana – Oldest reptile?
Late Mississippian of Scotland
Hylonomus lyelli
30 cm long. Joggins Cliffs, Nova Scotia
Found in tree stumps
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Pelycosaurs
Fin-backed reptiles
Evolved in Pennsylvanian; dominant by Permian
Herbivores and Carnivores
Sail back used for? Sexual display
Protection
Scary display
Thermoregulatory device Capture sun’s heat
Turn to wind for cooling
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Dimetrodon
Dimetrodon
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Therapsids – Mammal-like Reptiles
Therapsids were small- to medium-sized animals displaying the beginnings of many mammalian features
fewer bones in the skull because many of the small skull bones were fused
enlarged lower jawbone
differentiation of the teeth for various functions such as nipping, tearing, and chewing food
more vertically placed legs for greater flexibility,
as opposed to the sideways sprawling legs in primitive reptiles
Evolved in the Permian and radiated after extinction of ancestral pelycosaurs
Therapsids with hypothetical fur; endothermic?
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Fate of the Reptiles
66% of reptiles and amphibians became
extinct in the Permian/Triassic mass
extinction event
Reptiles radiated in the Mesozoic to
become dominant animal life form
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Evolution of Plants
The earliest record of plants on land is
palynological.
Upper Ordovician
plant spores and
cuticle from Lybia
Palynology (Read Perspective
13.1)
Study of various organic microfossils
called palynomorphs.
Includes: Pollen, Spores, Acritarchs,
Dinoflagellates and plant parts such as
wood and cuticle.
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Fossil Algae Ancestors
Earliest Land Plants
Small Y-shaped stems , leafless, with
sporangia at tips, resistant cuticle and
spores typical of lower vascular plants
Rhizome rather than true roots
Low, wet, marshy, freshwater environment
Needed moisture for sperm to reach egg.
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Earliest Land Plants
Cartoon of
Cooksonia
earliest known
land plant
Cooksonia
Cooksonia pertoni with sporangia
South-Wales
Pridolian (Upper Silurian)
Height of the plant 3.7 cm.
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Lower Vascular Plants
Reproduce sexually with a gametophyte
generation; small inconspicuous.
Fern gametophytes growing
in a terrarium
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Spores of lower vascular plants
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The Seed Plants - Gymnosperms
Heterosporic ancestors
Intermediate between lower vascular
plants and Gymnosperms
Two types of spores: 1 female, 1male
Megaspore – Large, ornate, female
Miospore – small (1/3 size) less ornate, male
Early Devonian
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Megaspores
Miospores
Chaleuria cirrosa Fossil Heteroporus plant
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Before the Gymnosperms
Progymnosperms
Fernlike reproduction and
leaves
Gymnosperm anatomy
Middle and Late Devonian
Archaeopteris halleri
Stump of Calixylon
Archeopteris
Fernlike leaves,
Gymnosperm wood
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Late Devonian Gymnosperm
Groups
Seed Ferns - Pteridospermatophyta
Extinct group with fern-like leaves
Produced seeds and pollen
Conifers
Cone bearing plants
Produced seeds and pollen
Fossil seed fern
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Seed Fern seeds
Lebatia Walchia
Fossil Conifers
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Fossil cones of conifers
Aracaria
Carboniferous Coal Swamps
Mostly seedless vascular plants Grown into trees of heights of 30m or more
Lycopsids Lepidodendron
Sigillaria
Shed palm-like leaves as they grew; leaves only at the top; leaf scars along trunk
Sphenopsids – Horsetail trees Calamites
Jointed stem/trunk
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Coal Swamp Plants
Lepidodendron
Coal Swamp Plants
Sigillaria
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Coal Swamp Plants
Calamites
Higher ground in the Carboniferous
Gymnosperms
Cordiates- tall trees (50m high)
Glossopteris –Gondwanaland marker
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Gymnosperms of the
Carboniferous
Cordiates
Mazon Creek deposits
Gymnosperms of the
Carboniferous
Glossopteris
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Fate of the Late Paleozoic Plants
Pangea – warmer and drier on land
Cordiates become extinct at end of Permian
Lycopsids and Sphenopsids reduced to small creeping plants
Dry tolerant Gymnosperms dominate Permian and survive the Permo/Triassic extinction event to dominate Triassic and Jurassic.
Club Moss