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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