Evolution of Tetrapod Vertebrates

inferred from fossil record

Labyrinthodonts – first tetrapod amphibians

Rhipidistians – crossopterygian lobe-finned fish

(Sarcopterygii)

Placoderms – first jawed fishes

Ostracoderms – jawless fishes

Cladogram of key taxa in evolution of tetrapods

Eusthenopteron foordi (Sarcopterygii: Crossopterygii) Devonian Quebec

Panderichthys rhombolepis (Sarcopterygi: Crossopterygii)

Devonian Latvia

Tiktaalik rosseae

Sarcopterygian Fish

Devonian 375 MY

Labyrinthodont amphibians - the earliest tetrapods

Carboniferous

Ichthyostega

Acanthostega

Acanthostega

Labyrinthodont Amphibian

Acanthostega

Labyrinthodont Amphibian

facweb.furman.edu

Eusthenopteron and Acanthostega

classical reconstruction

Behavior of fossil species can be difficult to interpret

Frogfishes (Antennarius)

have limb-like fins but

they never leave the

water …

Periophthalmus

…but mudskippers

do, and they don’t

even have lungs

Sarcopterygians, do have

lungs

African lungfishes cuaght

in small water-hole

Sarcopterygians do have

lungs

African lungfishes caught

in small water-hole

Ichthyostega – a temnospondyl labyrinthodont

Ichthyostega – a temnospondyl labyrinthodont

...had 7 toes!

facweb.furman.edu

Sclerocephalus - a temnospondyl labyrinthodont

Eryops – a temnospondyl labyrinthodont

fin-foot intermediates

CA Boisvert et al. Nature (2008) doi:10.1038/nature07339

Eusthenopteron Panderichthys Tiktaalik Acanthostega

Evolution of Reptiles from Amphibians

inferred from fossil record

Synapsids – mammal-like reptiles

Diapsids – Lepidosaurs (lizards, snakes)

and Archosaurs (“ruling reptiles” dinosaurs, crocodiles, birds)

Cotylosaurs (Anapsids ) – stem reptiles

Anthracosaur Labyrinthodonts –tetrapod amphibians