Distinguishing Features: Distinctive markings, small size, stout muzzle
Diet: Feeds almost entirely on plants
Unique Traits: Last surviving member of the subfamily Tremarctinae
Tremarctinae Subfamily
Common Name: Short-faced bears (name from early researchers, considered a misnomer today)
Distinctive Ancestors:
Arctodus simus (North America, early Pleistocene Epoch): Large enough to look a full-grown person in the eye on all fours.
Arctotherium angustidens (South America): Specimen found in Buenos Aires, more than 3 meters tall on hind legs.
Evolution and Adaptation
Early Ancestors:
Plionarctos: Lived in North America around 7 million years ago (Miocene Epoch), ancestor to all Tremarctines.
Lesser Short-Faced Bear: Appeared around 2.5 million years ago, size of large American black bears.
Arctodus simus: Appeared roughly 1.6 million years ago, up to 1.5 meters at the shoulder, weighed more than a ton.
Distribution: Fossils found across North America (Ozark Caves, La Brea Tar Pits, Alaska, Mexico)
Potential Migratory Adaptations: Migration to South America through land bridge (Great American Biotic Interchange around 2.6 million years ago in the late Pliocene Epoch).
Genetic Evidence
2016 Study: DNA from a fossilized femur of Arctotherium compared to genomes of living/extinct bears.
Findings: Arctotherium closer to modern spectacled bear than to Arctodus.
Implications: Mega-bears of North and South America evolved large sizes independently.
Evolutionary Pressures
Arctotherium angustidens:
Response to South America's unique environment (large herbivores, few predators).
Adaptations: Larger bodies to hunt/scavenge large herbivores.
Diet Study (2009): Skulls suggest omnivorous diet, not strictly carnivorous.
Arctodus simus:
Long, slender limbs, initially thought as evidence of predatory behavior.
More recent view: Possible scavengers practicing kleptoparasitism.
Diet Study: Mixed diet of plants and meat, evidence of sugary plant foods in diet.
Decline and Extinction
Arctotherium angustidens: Died out around 800,000 years ago, descendants became smaller and more herbivorous.
Arctodus simus: Disappeared around 10,000 years ago.
Potential reasons: Decline in Ice Age megafauna, competition from modern bears (genus Ursus).
Legacy
Spectacled Bear: Last remaining member, carries the legacy of Tremarctinae.
Closing & Additional Resources
Thanks to Supporters: Special thanks to contributors on Patreon like Jake Hart, Jon Ivy, John Davison Ng, and STEVE.
Further Learning: Suggested episode on bone-crushing dogs.