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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
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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
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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
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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
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“Apes” are a paraphyletic group
guenons gibbons orang gorilla chimps human
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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
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Evolution of Archosaurs
or “ruling reptiles”
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A) Tarbosaurus and B) Tyrannosaurus skulls1) left lateral, 2) dorsal
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Nanotyrannosaurus skull
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Left posterior femur and left lateral pelvis
Saurischian (Antrodemus) Ornithischian (Thescelosaurus)
(Hogervorst, Bouma, and de Vos 2009 Acta orthopaedica 80:1-39)
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Digitigrade
Deltopectoral crest
AntitrochanterPosture
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metatarsals
tarsals
intertarsaljoint