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The Cenozoic. Tectonics. Tectonics of the Mesozoic and Cenozoic. Major Mammal Groups. Multituberculates - now extinct - rodent-like mammals who lived from Jurassic to Oligocene and were probably outcompeted by modern rodents – longest lived of all groups!

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TheCenozoic


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Tectonics

Tectonics of the Mesozoic and Cenozoic


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Major Mammal Groups

  • Multituberculates - now extinct - rodent-like mammals who lived from Jurassic to Oligocene and were probably outcompeted by modern rodents – longest lived of all groups!

  • Monotremes - only three species still alive, duck-billed platypus and two species of echidna (long-nosed and short-nosed spiny anteaters), all found in Australia and New Guinea


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Major Mammal Groups

  • Metatheria (Marsupials) - Important group of mammals - originated in Middle Cretaceous as opossum-like organisms. They give birth to live, immature offspring.

  • Eutheria (Placental mammals) - Give birth to live young, often very mature functional organisms. Provide support for developing offspring through placenta connecting it to mother’s blood supply.





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Monotremes

  • A mix of primitive, standard mammal, and advanced features

  • They lay eggs like birds or reptiles

  • They support their young with milk

  • They have standard mammal skull structure

  • They have very specialized parts (e.g. nose parts, webbed feet)

  • Platypuses are even venomous!


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Monotremes

  • Monotremes have no teeth as adults (some have teeth as young)

  • Eggs are small (1/2 to 3/4 inch in diameter) and leathery; in platypus only the left ovary works

  • Probably split from other mammals sometime in Mesozoic - the earliest fossil is from the Cretaceous

  • Some possible monotreme fossils found in Argentina - could they have been widespread at one time?




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Marsupials

  • Originated in North America around Middle Cretaceous

  • Rapidly spread to South America and then to other parts of the world (scattered fossils found in Europe, Asia, the Americas), but faded away from North America by the Miocene when placental mammals entered the scene

  • Marsupials recolonized the Americas during the Pliocene.


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Marsupials

  • Young are born after only 8-40 days of gestation

    What is the problem they are trying to solve?

  • Rejection by mother’s immune system

    What’s better, marsupial reproduction or placental?

  • Not clear, but placentals have outcompeted marsupials most places where they have been in conflict


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Marsupials

  • Lots of forms of marsupials which are parallel to placental forms have existed at various times

  • There have been big marsupial grazers, marsupial dogs, cats, rodents, even a lion-like marsupial with retractable claws

  • Kangaroos and their relatives are an exception - no known parallel among other mammals. They’ve been more diverse in the past too - one ten-foot high species existed.


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Placental Mammals

  • Includes most mammals we think about - whales, bats, elephants, shrews, and armadillos

  • All give birth to live offspring after extended gestation

  • Sometimes offspring are fairly helpless for long periods after birth; other times offspring are fairly mobile

  • All require mother’s milk for support for at least a while (like other mammals)


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Placental Mammals

  • First showed up no later than Upper Cretaceous, possibly earlier (early fossils haven’t been definitively split between marsupials and eutherians)

  • Eutherians were widespread in Asia by the K-T

  • Many modern groups were around at or near the start of the Cenozoic, and all modern groups were in place by the end of the Miocene.


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Early Cenozoic Mammals

  • Paleocene –

    • Mammals diversify, spread

    • Insectivores and rodents common

    • Some grazers, but not huge ones yet

    • Many are “primitive” and lack the specializations they will later evolve – i.e., they are generalists.

Info and images from M. Jehle, Paleocene Mammals of the World,

http://www.paleocene-mammals.de



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Multituberculates

Paleocene multituberculate Ptilodus, about 50 cm in length


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Paleocene Mammals

Ectoconus – Paleocene herbivore; size of goat or sheep


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Paleocene Mammals

Purgatorius, possible ancestor to later primates


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Paleocene Mammals

Ectoganus and two Pantolambda – digging for food


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Paleocene Mammals

Plesiadapis, anoter possible ancestor to later primates


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Paleocene Mammals

Carpolestes, from late Paleocene


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Paleocene to Eocene

Chriacus – larger, more mobile


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Paleocene to Eocene

Phenacodus – sheep-sized herbivore – note the feet


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Eocene

Oxyaena - predator


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Eocene

Pachyaene attack Diatryma (~8 feet tall)


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Big guys

Elephant-sized Titanotheres


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Big guys

Uintathere and early horse ancestors in the Eocene





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Andrewsarchus

Sarkastodon (member of creodonts; dominant predators from 55-35 Ma)

6’ at shoulder; could kill a modern elephant

Brontothere – rhino sized herbivore


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Big guys

Irish Elk – largest deer variety ever; from Pleistocene; not restricted to Ireland, but good fossils found there


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Big guys

Mastodon – Pliocene to end of Pleistocene – ate leaves


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Big guys

Mammoth – Pliocene to 1500 BCE (dwarf species survived on Wrangel Island, Russia) – ate grasses


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