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 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

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

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

Closer Look…

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

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

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

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

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

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

South America Porcupines Glyptodonts Armadillos Ground Sloths Opossums

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

Sloth Diversity Bear sized Bassett sized

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

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

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

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

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

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

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

So, What Do You Think? Eurotamandua Ernanodon

Questions?

Thank You! Choloepus didactylus Choluis ruedas