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Xenarthran Biogeography

Xenarthran Biogeography. The South American Experiment Of Speciation and Biogeography. Superorder Xenarthra. Recently divided into two Orders Pilosa – anteaters and sloths Cingulata – armadillos, glyptodons, and pampatheres. Strong Support for Monophyly.

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Xenarthran Biogeography

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  1. Xenarthran Biogeography The South American Experiment Of Speciation and Biogeography

  2. Superorder Xenarthra • Recently divided into two Orders • Pilosa – anteaters and sloths • Cingulata – armadillos, glyptodons, and pampatheres

  3. Strong Support for Monophyly • Unique traits unite these very different morphotypes (examples) • Xenarthrous articulations of the vertebrae • Dermal ossifications (Armadillos and some Ground Sloths) • Lacking protein in eye – all extant xenarthrans lack and all other mammals have this protein

  4. Origin • Strong support for originating in South America after Gondwana separated – 100 to 90 MYBP • First fossil evidence – armadillo scute in Argentina – Paleocene ~60 MYBP • Molecular clock ~65-100 MYBP

  5. Fossils • Currently, 31 species in 5 Families • About 150 extinct species in 8-10 Families (depending on source) • Found from Argentina to Alaska

  6. Closer Look…

  7. ~90 Million Years • Three groups of mammals on South America – The Old Timers • Marsupials • Ungulates • Xenarthrans

  8. Second Wave • Primates and Rodents arrived from Africa while South America was still isolated • Date is highly debated –30 MYBP? • Xenarthrans – massive speciation event at this time

  9. Fossils • During this time, fossils are found throughout South America, primarily in Argentina

  10. 9 Million Years Ago • 3 Families of Ground Sloths arrive in Florida before the Isthmus of Panama • Island Hopping – sea levels beginning to drop

  11. Great American Biotic Exchange • Isthmus of Panama arises – beginning about 9 million years ago, and completed about 3 million years ago • Mammals from North America migrate South • Mammals from South America migrate North

  12. North American Mammals Win • Rabbits • Field mice • Foxes • Bears • Raccoons • Weasels • Cats • Mastodons • Horses • Tapirs • Peccaries • Camels • Deer

  13. South America • PorcupinesGlyptodontsArmadillosGround SlothsOpossums

  14. Sloth Success • Diversified into new species (largest in North America: Eremotherium ~ 7.3 meters (22 feet) • Migrated as far north as Alaska

  15. Sloth Diversity Bear sized Bassett sized

  16. Xenarthran Diversity • Largest – Megatherium americanum 11+ meters (33 feet) • South American

  17. Xenarthran Diversity • Smallest – Pink Fairy Armadillo (Chlamyphorus truncatus) 25cm (5 inches) Humeri of Zaedyus and Eremotherium

  18. Glyptodons • Up to 3+ meters long, 2 meters high, encased in bone • Evidence of muscle scaring on face indicates that they may have had small trunks • Mid-US migration

  19. Anteaters • One fossil giant anteater was found in Sonora, Mexico from the Pleistocene – North America • Anteaters have an extremely poor fossil record

  20. Ground Sloths and Glyptodons • Extinction • Ice ages? • Human hunting? • Disease? • Combination? • Something else? • Extinct first in North America, then South America, then islands

  21. How About This? • Fossil found in Messel, German from the Eocene (35-57 MYBP) • Eurotamandua jorsii thought to be a tamandua (lesser anteater) • Placed in Xenarthra

  22. Or This… • Fossil found in Guangdong, China from the Paleocene (57-65 MYBP) • Ernanodon antelios thought to be “sloth-like” • Placed in Xenarthra

  23. So, What Do You Think? Eurotamandua Ernanodon

  24. Questions?

  25. Choloepus didactylus Choluis ruedas Thank You!

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