By Chelsea Whyte
Fossils of extinct bears and wolves from the end of the last glacial period have been discovered in an underwater cave in Mexico’s Yucatán peninsula. The finds could help us better understand how large prehistoric animals moved around the Americas.
With the help of professional divers, Blaine Schubert at East Tennessee State University and his colleagues found the trove of fossils in a cave whose floor is 55 metres below sea level. The site, called Hoyo Negro, would have been dry before melting glaciers filled it with water, helping to preserve the bones there.
The divers brought up intact skulls and other bones from two extinct animals. They found fossils from seven individuals of the Arctotherium wingei, a smaller cousin of the giant short-faced bears that lived in South America during the Pleistocene and are thought to be the largest bears ever.
Using well-preserved collagen from the roots of a tooth, Schubert and his team dated the bear’s bones to about 11,000 years ago. The team also found fossils of a wolf-like animal called Protocyon troglodytes.
“Typically as a palaeontologist, if I’m going on a caving trip looking for ice age animals, I’m lucky to find a tooth,” says Schubert. Hoyo Negro was at the intersection of three passageways through the caves, creating a natural trap where many animals met their death. “This pit had a lot of animal remains. The divers didn’t have to do any digging. These animals were just laying on the surface, and some have been there for 30,000 years.”
The fossil record in Central America for this time is quite sparse, so this cache is helping to fill in gaps in our understanding of how these animals migrated throughout the Americas. Before this expedition, it was thought that the bear and wolf-like animal were only present in South America during this period.
About 3 million years ago, the Panama isthmus rose and created a land bridge between North and South America, enabling what is known as the Great American Interchange – a period in which Arctotherium and Protocyon were thought to have migrated south and stayed. “We had no record of these animals making it back across that isthmus again until now,” says Schubert.
Journal reference: Royal Society Biology Letters, DOI: 10.1098/rsbl.2019.0148