African, Arabian Mammals Didn’t Escape Grande Coupure Extinction

The scientists also examined a collection of dental fossils from Egypt and stored at the Duke Lemur Center Division of Fossil Primates (DLCDFP) from five mammal groups: extinct carnivores called hyaenodonts, two rodent groups (anomalures and hystricognaths), and two primate groups—the strepsirrhines, which includes lemurs, their close relatives, and their ancestors, and the anthropoids, the lineage that led to humans. The researchers looked at lower teeth to extract information about the animals’ diets and, in turn, the environment where they lived. “We see a huge loss in tooth diversity, and then a recovery period with new dental shapes and new adaptations,” lead author and University of Salford archaeologist Dorien de Vries says in a press release about the paper.

Seiffert explains in the release that diversity in modern humans’ anthropoid ancestors “bottoms out to almost nothing around 30 million years ago, leaving them with a single tooth type,” and that this “ancestral tooth shape determined what was possible in terms of later dietary diversification.”

Paleontologist Chris Beard, who was not involved with this study, tells Inside Science that he does not find the results particularly surprising. Though, he notes that “this result could be viewed as counterintuitive, especially for arboreal primates and rodents” whose species evolution would likely be supported by the forest patches of the early Oligocene. “So, either the assumption of increasingly patchy conditions across the Eocene-Oligocene boundary is wrong, or the macroevolutionary response to it was different than expected.”

Seiffert offers some thoughts in his Nature Ecology and Evolution piece as to why these mammals went extinct, suggesting global cooling followed by persistent volcanic activity drastically changed the landscape and environment, making it unsuitable over a span of several millions of years. He writes that the team wants to expand the dataset in the future using the same methods, but “the real challenge is to expand the search for Oligocene mammals in Africa and Arabia, so that we can more thoroughly evaluate the nature of this previously ‘hidden’ extinction event.”

Coauthor and paleontologist Hesham Sallam notes in the press release that this is yet another example of how climatic changes “have shaped the evolutionary tree of life,” adding that “Collecting evidence from the past is the easiest way to learn about how climate change will affect ecological systems.”