The Phanerozoic Eon

Eras Periods comments

Paleozoic 541-252 MYA Pangean supercontinent

Cambrian

Ordovician

Silurian

Devonian

Carboniferous

Permian ends with first great extinction

Mesozoic 252-66.5 MYA (“Age of Reptiles”) Laurasia and Gondwana supercontinents

separated by equatorial Tethys Sea

Triassic

Jurassic

Cretaceous ends with second great extinction

Cenozoic 66.5 MYA-present (“Age of Mammals”) modern continents

Paleogene

Neogene

Era Periods comments

Mesozoic 252-66.5 MYA (“Age of Reptiles”) Laurasia and Gondwana supercontinents

separated by equatorial Tethys sea

hotter and arid

TriassicGymnosperms dominant

first mammal-like reptiles

first dinosaurs

Jurassicformation of Atlantic Ocean begins

development of continental seaways

first birds

CretaceousAngiosperms dominant

ends with second great extinction

Monophyly – the property of an inclusive group of organisms of shared common ancestry

a b c d e

a b c d e

a b c d e

Polyphyly – the property of being unrelated by descent

Paraphyly – the property of a group of organisms of shared common ancestry that does not include all of the evolutionary derivatives of that common ancestor

Monophyletic groups are the only onesintended to be classified taxonomically

a b c d e

a b c d eParaphyletic groups are undesirable in classification because those organisms most closely related (i.e., a and b) are not grouped together

-most likely to have been based on superficiallyconspicuous traits, therefore many examples discoveredwith the application of molecular data to large samples

“Apes” are a paraphyletic group

guenons gibbons orang gorilla chimps human

Evolution of Reptiles from Amphibians

inferred from fossil record

Anthracosaur Labyrinthodonts –tetrapod amphibians

Cotylosaurs (Anapsids ) – stem reptiles

Diapsids – Lepidosaurs (lizards, snakes)

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

Synapsids – mammal-like reptiles

Evolution of Archosaurs

or “ruling reptiles”

A) Tarbosaurus and B) Tyrannosaurus skulls1) left lateral, 2) dorsal

Nanotyrannosaurus skull

Left posterior femur and left lateral pelvis

Saurischian (Antrodemus) Ornithischian (Thescelosaurus)

(Hogervorst, Bouma, and de Vos 2009 Acta orthopaedica 80:1-39)

Digitigrade

Deltopectoral crest

AntitrochanterPosture

metatarsals

tarsals

intertarsaljoint