Research Sheds New Light on How Cave Bears Became Vegetarians
A Middle Pleistocene cave bear, also known as the Deninger’s bear (Ursus deningeri), is generally regarded as the direct ancestor of the mostly vegetarian cave bear (Ursus spelaeus), and the transition between the two species took place around the Middle-Late Pleistocene boundary, about 126,000 years ago. Until now, very little was known about the dietary evolution of cave bears and how they became vegetarians, as the fossils of Deninger’s bear are extremely scarce. However, a study by paleontologists in Germany and Spain sheds new light on this.
To understand the evolution of the cave bear lineage, Dr. Anneke van Heteren from the Zoologische Staatssammlung München and the Ludwig-Maximilians-Universität München and colleagues compared the mandibles and skull of the Deninger’s bear with that of classic cave bears and modern bears.
They micro-CT scanned the rare fossils and digitally removed the sediments so as not to risk damaging the fossils.
“The analyses showed that Deninger’s bear had very similarly shaped mandibles and skull to the classic cave bear,” Dr. van Heteren said.
“This implies that they were adapted to the same food types and were primarily vegetarian.”
“There is an ongoing discussion on the extent to which the classic cave bear was a vegetarian,” added study co-author Mikel Arlegi, a doctoral candidate at the Universities of the Basque Country and Bordeaux.
“And, this is especially why the new information on the diet of its direct ancestor is so important, because it teaches us that a differentiation between the diet of cave bears and brown bears was already established by 500,000 years ago and likely earlier.”
Interestingly, the team also found that there are shape differences between Deninger’s bears from the Iberian Peninsula and those from the rest of Europe, which are unlikely to be related to diet.
“There are three possibilities to explain these differences: (i) the Iberian bears are chronologically younger than the rest; (ii) the Pyrenees, acting as natural barrier, resulted in some genetic differentiation between the Iberian bears and those from the rest of Europe; or (iii) there were multiple lineages, with either just one leading to the classic cave bear, or each lineage leading to a different group of cave bears,” they said.
“However, more fossils are necessary to test these hypotheses,” said co-author Dr. Asier Gómez-Olivencia, from the University of the Basque Country.
Anneke H. van Heteren et al. Cranial and mandibular morphology of Middle Pleistocene cave bears (Ursus deningeri): implications for diet and evolution. Historical Biology, published online July 26, 2018; doi: 10.1080/08912963.2018.1487965