Vertebrate EvolutionTorsten Bernhardt

Redpath Museum, McGill University

This teaching resource was made possible with funding from the PromoScience programme of NSERC.

© McGill University 2010

History of the Earth

4.6 3.8-3.5 1.5 0.542 0

Origins of Bacteria

Origins of Eukaryotes

Phanerozoic

Paleozoic Mesozoic Cenozoic

(Billions of years)

(Millions of years)

Chordates

Pikaia

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Tunicates (sea squirts)

The First Fish?

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Haikouichthys

Agnathans: Jawless Fish (i)

Ostracoderms-armoured, jawless fish-used gills only for respiration-no paired fins, so probably poor swimmers

Endeiolepis aneri

Agnathans: Jawless Fish (ii)

Cephalaspisht

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Ostracoderms went extinct in the Devonian, most likely due to the placoderms (who we’ll get to in a minute…)

Agnathans: Jawless Fish (iii)

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A modern agnathan: the lamprey

Placoderms: Jaws Evolve (i)

Bothriolepis

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-Still armoured-Jaws are a major advantage-First live birth-Paired fins

Placoderms: Jaws Evolve (ii)ht

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Dunkleosteus

No teeth

Cartilaginous Fish (Chondrichthyes) (i)ht

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Manta ray

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Fish/chimaera_fish1.jpg

-Sharks, skates, rays, chimeras-Skeleton is made of cartilage instead of bone-Don’t fossilize well-Are thought to have evolved from placoderms

Chimeraht

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Great white shark

Cartilaginous Fish (Chondrichthyes) (ii)ht

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Stethacanthus(~360 Mya)

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Megalodon (~1.5 mya)

Bony Fish (Osteichthyes)ht

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-store.co.uk/wp-content/uploads/2009/01/beta-fish-pictures.jpgNile Perch

Betta

Bony Fish – Ray-finned Fish(Actinopterygii)

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Brook trout

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Clown fish

-25 000 species, 99% of all fish today-Fins are supported by bony rays

Homalacanthus

Bony Fish – Lobe-finned Fish(Sarcopterygii)

Eusthenopteron

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Coelacanth

-Fins have bones and muscle-Live on the bottom-Not especially diverse, as fish

From Fish to Amphibians

One group of sarcopterygians, the osteolepiforms, had nostrils that led to an opening in the roof of its mouth. This allowed air to pass into the mouth and then to paired swim bladders (similar to our lungs).

Lungfish, which are modern sarcopterygians, can crawl over land from one water body to another.

The sturdy fins of the sarcopterygians have bones much like those in our limbs. Other anatomical features, such as skull bones and teeth, also point to a relationship.

We think that amphibians evolved from sarcopterygian (lobe-finned) fish. Why is this?

From Fish to Amphibiansht

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Amphibian limb (left) and lobe-finned fish fin (right)

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Early amphibians had as many as eight toes; this was eventually reduced to five, or four

Amphibiansht

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Ichthyostega

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Acanthostega http

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-Early amphibians didn’t look like modern amphibians

-Three-chambered heart-Had lungs, but also breathed through

their skin-Were tied to water for reproduction-Dominant predators in the Carboniferous

Amniotes

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Amni

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Amniote egg

Outer envelope

Inner envelope

Yolk Amphibian egg

-Amniotes’ eggs allowed them to reproduce away from water and expand to drier areas

-They diverged into two lineages: one would eventually become mammals, the other would become reptiles and birds

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Chroniosuchus, which may be an ancestor of amniotes

Mammal-like reptiles (Synapsids)

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Dimetrodon

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Gorgonopsids

-Ancestors of true mammals-Regulated their temperature-Different types of teeth-Very successful until the end of the Permian

The Permian Extinction

!

-The most severe extinction event in the Earth’s history-May be related to the Siberian Traps, the largest volcanic

eruptions on Earth-96% of species in the oceans go extinct, 70% of vertebrates on

land go extinct, 99.5% of all living creatures die-The mammal-like reptiles are severely affected

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Reptileshttp://w

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Scutosaurus

-Many different groups-Scales, “3.5”-chambered heart-Almost all lay eggs-Extremely successful in the Mesozoic (which is

known as the Age of Reptiles)

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Mesosaurus, one of the first reptiles to return to the sea

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Coelurosauravus, a gliding reptile

Crurotarsi

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Postosuchus

-The group that today includes crocodiles

-Ruled the world in the Triassic, after the mammal–like reptiles were severely affected by the Permian extinction

-Were themselves severely affected by the extinction event at the end of the Triassic

Other Reptilesht

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Green sea turtle

Snake

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Tokay gecko

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Tuatarahttp

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Dinosaurs

Triceratops Gorgosaurus

-Were around for 160 million years

-Two groups, based on hip structure

-May have been warm blooded

-Advanced features – bones, gait

Dinosaursht

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Not Just Dinosaurs! (i)

Turtles

Snakes

Lizardsht

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Crocodylimorphs

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Tuatara

Not Just Dinosaurs! (ii)ht

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Pterosaurs - the first flying vertebrates

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Mosasaurs

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Ichthyosaurs

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Plesiosaurs

True Mammals

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-Evolved from the synapsids (mammal-like reptiles)

-Vaguely rodent-like, small

-Showed up not too long after the dinosaurs

-Didn’t amount to much in the Mesozoic; lawnmower ecology

Birdsht

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Archaeopteryx

-Evolved from dinosaurs; specifically, the meat-eating deinonychosaurs, which includes Dromaeosaurus

-Are technically dinosaurs

-Feathers evolved before birds did; T. rexmay have been fuzzy

-May have outcompeted the pterosaurs and helped drive them to extinction

-The second vertebrate group to fly

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Cretaceous Extinction

!

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-Ends the reign of the dinosaurs

-Flying and swimming reptiles also go extinct

-Many other groups suffer as well

-Mammals step into the empty niches

Mammals Take Over (i)ht

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Indricotherium

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Panochthus_frenzelianus.jpg

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Arsinoitherium

Glyptodont

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Leptictidium

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Saber-toothed cat

Mammals Take Over (ii)ht

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Humpback whale

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Bat

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