Transcript Transitional Fossils

Punctuated Equilibria
• A term coined by Stephen Jay Gould &
Niles Eldredge (1972)
• The idea
– Most of the time there is no change
– Occasionally, change happens very quickly
• This is mainly true
– The speed of evolutionary change is variable
– Sometimes slow, sometimes fast
– So neither extreme view is fully correct
© Colin Frayn, 2008
www.frayn.net
Transitional Fossils
• How many are there?
– The claim that no transitional fossils exist is hugely false
– Many fossil sequences exist, joining every major stage of
evolution
• How many do we expect?
– Fossils are very hard to find
• Large parts of the planet have never been adequately searched
• Huge efforts in China are now providing lots of new finds
– When we do find lots, it’s unsurprising that they are all very
similar
• The local conditions were good for fossilisation
• Perhaps only for a short period of time
– Several major transitions would have occurred rapidly
• We wouldn’t expect any transitional fossils
© Colin Frayn, 2008
www.frayn.net
Reptiles to Birds
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Therapod dinosaurs …
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Coelophysis (late Triassic)
Compsognathus (Jurassic)
Deinonychus, Oviraptor, and other advanced theropods (late Jurassic,
Cretaceous)
Lisboasaurus estesi & other "troodontid dinosaur-birds" (mid-Jurassic)
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– GAP: The exact reptilian ancestor of Archeopteryx is unknown
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Protoavis (Triassic, ~225 Ma) -- A highly controversial fossil that may or
may not be an extremely early bird.
Archeopteryx lithographica (Late Jurassic, 150 Ma)
Sinornis santensis ("Chinese bird", early Cretaceous, 138 Ma)
Iberomesornis, Concornis and Eoalulavis (early Cretaceous, 135 Ma)
Ambiortus dementjevi, Yanornis (early Cretaceous, 125 Ma)
Gansus (Cretaceous 110 Ma)
Hesperornis, Ichthyornis, and other Cretaceous diving birds (94-75 Ma)
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… Modern birds
© Colin Frayn, 2008
www.frayn.net
W E Swinton’s Quote
• Claimed that bird evolution has no
evidence
– Writing in 1960!
• Well, he was more-or-less right in 1960…
• Since then, we’ve learned a lot!
© Colin Frayn, 2008
www.frayn.net
Horse Evolution
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Early perissodactyls …
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Loxolophus: (early Paleocene)
Tetraclaenodon: (mid-late Paleocene, ~64 Ma)
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SMALL GAP: There are almost no known perissodactyl fossils from the late Paleocene. Should be solved with new Asian
fossil hunts
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Radinskya yupingae: (late Paleocene, ~55 Ma, China)
Hyracotherium: (early Eocene, about 55-45 Ma; previously "Eohippus")
Hyracotherium vassacciense: (early Eocene, ~55 Ma)
Orohippus: (mid-Eocene, ~50 Ma)
Epihippus: (late Eocene, ~45 Ma)
Mesohippus celer: (late Eocene, 40 Ma)
Mesohippus westoni: (early Oligocene, ~37 Ma)
Miohippus assiniboiensis: (mid-Oligocene, ~37 Ma)
Kalobatippus: (late Oligocene, 24 Ma)
Parahippus: (early Miocene, 23 Ma)
'Parahippus' leonensis: (mid-Miocene, ~20 Ma)
Merychippus gunteri: (mid-late Miocene, 18 Ma)
Merychippus primus: (mid-late Miocene, 16 Ma)
Merychippus: several other species of mid-late Miocene (18-15 Ma)
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SMALL GAP: It is not known which Merychippus species (stylodontus? carrizoensis?) gave rise to the first Dinohippus
species
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Dinohippus: (late Miocene, 12 Ma)
Equus (Plesippus): also called the "E. simplicidens" group (Pliocene, ~4 My)
Equus (Hippotigris): (Pleistocene, 2Ma)
Equus (Equus): (Pleistocene, 2Ma)
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… Modern horses
© Colin Frayn, 2008
www.frayn.net
Whale Evolution
• Semi-aquatic mammals …
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Hapalodectes: Early Eocene (55 Ma)
Pakicetus inachus: Early Eocene (53 Ma)
Ambulocetus natans: Early to Middle Eocene (50-49 Ma)
Rodhocetus: Mid-Eocene (47 Ma)
Remingtonocetus: Middle Eocene (46-43 Ma)
Indocetus ramani: earliest Middle Eocene
Prozeuglodon : Mid Eocene (40 Ma)
Dorudon: Mid-to-late Eocene (41-33 Ma)
Basilosaurus: Mid-to-late Eocene (40-34 Ma)
Eocetus: Late Eocene (35 Ma)
Squalodon: Oligocene - Miocene (33-14 Ma)
Cetotherium: Mid Miocene (15 Ma)
• … Modern whales
© Colin Frayn, 2008
www.frayn.net