It’s always surprising when studies of an animal’s genetic history yield unexpected results, and the latest look at spectacled bear (Tremarctos ornatus) DNA is no exception. The study (referenced below) examined 3 specimens of the extinct giant short-faced bear (Arctodus simus) and 1 specimen of the extinct Arctotherium sp. and compared their genetics with that of the extant spectacled bear. The giant short-faced bear specimens came from the Yukon and Alaska and dated to ~47,000 years BP and ~24,000 years BP. The Arctotherium specimen came from Chile and dated to 12,000 years BP. Although Arctotherium anatomically resembled A. simus, results of the study determined the 2 species never interbred. The giant short-faced bear was a North American species, and Arctotherium was a South American species, but their ranges did overlap in Mexico. However, the study indicated the extinct Arctotherium did hybridize with the extant spectacled bear during the late Pleistocene. Both are South American species and their ranges did overlap extensively. This is a surprising result because scientists estimate the ancestor of the spectacled bear diverged from the ancestor of Arctotherium about 3.6 million years ago, and they were quite distinct species.
Spectacled bear–the only extant tremarctine bear. Genetic evidence from a new study suggests they occasionally interbred with the extinct Arctotherium bears during the late Pleistocene and they also interbred with the common ancestor of modern grizzly and black bears during the Pliocene.
Artist’s depiction of the extinct Arctotherium.
The study produced an additional surprising result, but before I discuss this I need to digress and explain the 2 lineages of bears. Ursine bears (black, grizzly, polar, Asiatic black, sun, and sloth) diverged from tremarctine bears about 10 million years ago. The spectacled bear is the only tremarctine bear still extant, but during the late Pleistocene there were 3 additional species including the giant short-faced, Arctotherium, and the Florida spectacled bear (T. floridanus). Results of this study suggests the ancestor of the South American spectacled bear did hybridize with the common ancestor of the black bear and grizzly bear. The ancestor of black bears diverged from the ancestor of grizzly bears at least 1.5 million years ago, so this hybridization event likely occurred during the Pliocene. The giant short-faced bears and Arctotherium never hybridized with ursine bears, but different species of ursine bears hybridized with each other numerous times.
In the future it would be interesting to see the results of a genetic study of T. floridanus. The Florida spectacled bear ranged throughout southeastern North America during the Pleistocene and it shared the range with black bears. Did these 2 species ever hybridize?
Reference:
Salis, A.; et. al.
“Ancient Genomes Reveal Hybridization between Extinct Short-faced bears and the Extant Spectacled Bear (T. ornatus)
BioRxiv Feb 2021
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