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 ~ 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
Porcupines Glyptodonts Armadillos Ground Sloths Opossums

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. Thank You!
Choloepus didactylus
Choluis ruedas