Researchers diving in Mexico’s famous underwater cave, Hoyo Negro, have found the skeletal remains of Ice Age predators thought to only exist in South America at that time.

The Mexican and US team discovered the giant skull and other fossil remains of the long-extinct Arctotherium wingei, from the family of short-faced bears, thought to be the largest that ever lived, as well as the wolf-like Protocyon troglodytes.

Due to its tropical climate, parts of Mexico and Central America do not have a strong fossil record as conditions are not conducive to preserving ancient remains. However, this particular cave in the Yucatan Peninsula is providing a whole wealth of information on the fauna – including humans – of the late Pleistocene thanks to it being a natural trap.

Hoyo Negro (“Black Hole”), in the Sac Actun cave system, has a floor 55 meters (180 feet) below sea level, meaning around 11,000 years ago, these animals likely fell nearly 60 meters (197 feet) to their deaths. Though dry then, it would later fill up with melting glacier water as the Ice Age came to an end, helping preserve their remains, and those of many other creatures that have also been found.

Biology Letters
Part of the cranium of the Ice Age bear A. wingei found at the bottom of Hoyo Negro. (c) Roberto Chavez-Arce

The researchers first came across the cave in 2007, where they discovered what we now know is the oldest complete skeleton found in the Americas. Named Naia, the remains are of a teenage female who lived between 12,000 and 13,000 years ago and died around age 17.

In the years since then, skeletons of many creatures, both extinct and extant, have been found, including saber-toothed tigers, cougars, tapirs, ground sloths, elephant-like gomphotheres, bears, and canids, but it’s thought the understandable excitement over the teenage remains meant the two long-extinct species got overlooked, especially as it was assumed they never got this far north. They were misidentified as a member of the Tremarctos genus (spectacled bear) and the coyote Canis latrans.

Central America
The jawbone of P. troglodytes, found 2,000 kilometers from where it was thought to live. (c) Roberto Chavez-Arce

Because the fossil record is so sparse in Central America, this find is helping fill in some gaps about the distribution of large mammals that roamed Earth during the last Ice Age. In their new study focusing on A. wingei and P. troglodytes, published in Biology Letters, researchers revealed that finding these large predators more than 2,000 kilometers (1,200 miles) from home suggests a much more complex history of fauna in the Americas.

Between 2.5 million and 3 million years ago, during what is known as the Great American Biotic Interchange, land and freshwater animals crossed from North America via Central America into South America, and vice versa, thanks to a land bridge that formed and connected the formerly separate continents.

During one of these crossovers, ursids and canids crossed from north to south. These evolved into their own species, like the two found in the cave, only they have never been found outside of South America, so it had been assumed they stayed there. This discovery offers up two potential theories: that some of the large carnivores stayed in Mexico rather than traveling south, or that they recrossed the land bridge back into Central America. Hopefully, one day, more evidence will be able to confirm these events.

What cannot be underestimated is the importance of these underwater caves for offering us previously unknown glimpses into life as the last Ice Age was coming to a close.

Related posts