Warming shrank carnivorous mammals

Fossil pine contains a reduction trend in the climate maximum 55 million years ago

Pine of Palaeonictis wingi © Jennifer Duerden / University of Florida)
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Particularly rapid global warming 55 million years ago not only caused many herbivores to shrink, it also resulted in size reduction in free-range mammals. This shows a now discovered fossil of a previously unknown carnivore species whose genus shrank in the course of only 200, 000 years from bear to hyena size only. The causes of this shrinkage process are still unclear.

At the beginning of the Eocene, some 55 million years ago, the Earth experienced a strong global warming, the so-called Paleocene-Eocene Thermal Maximum (PETM). In just a few tens of thousands of years, average temperatures rose five to seven degrees, and the atmospheric concentration of the greenhouse gas carbon dioxide increased. At the same time many herbivorous mammal species of the time began to develop into smaller and smaller forms. Why, that is still controversial. According to one theory, the increased CO2 levels caused a decrease in nutrient content in plants, which in turn favored smaller herbivores.

Size reduction from bear to hyena

Now American scientists, led by Jonathan Bloch, Curator of Vertebrate Paleontology at the Florida Museum of Natural History, have discovered a fossil that sheds new light on the enigmatic "shrinkage" of mammals in the Eocene. In the Big Horn Basin of Wyoming, they found an almost complete jawbone of one of the group of Oxyaenidae, extinct carnivorous mammals, belonging to the animal. The unknown species, Palaeonictis wingi, baptized, is, with the size of a hyena, distinctly smaller than those of the genus found in North America from the preceding cooler period.

According to the researchers, this indicates that the genus Paleonictis of the at least bear-sized species Paleonictis peloria must have developed in the course of about 200, 000 years to the only about hyena-sized species Paleonictis wingi and the then living in Europe species Paleonictis gigantea. They see it as a clear reference to the prevailing climate optimum in this time, as they write in their article in the journal "Journal of Mammalian Evolution".

Stephen Chester (left) and Jon Bloch examine fossil pine Jennifer Duerden / University of Florida

Influencing factors still puzzling

"We know that herbivorous animals became smaller during the early Eocene when global warming began, presumably in the context of increased carbon dioxide levels" Stephenrt Stephen Chester from Yale University. Surprisingly, this study shows that the same thing happened to some carnivores. This points to other influencing factors in their evolution. The pine of the newly discovered species shows that the animal must have been an omnivore with a preference for meat meals. Therefore, its size was not dependent on plant nutrients. display

However, what factor might have been responsible for the very rapid shrinkage of this genre by evolutionary standards is not yet clear. In any case, according to Bloch, the new finds are also helpful in exploring the possible consequences of today's climate change. "Documenting the effects of past climate change is one of the experiments that can inform us about the effects that global warming on mammals may have in the near future", says the researcher.

(University of Florida, 03.09.2010 - DLO)