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Almost 63% of Afro-Arab mammal species became extinct around 30 million years ago (Oligocene epoch), after Earth’s climate changed from swampy to frigid.
A Pleistocene landscape. Image credit: Roman Uchytel, via the Netherlands Institute for Ecology.
In a new study, Dr Dorien de Vries and colleagues at the University of Salford examined fossils from five groups of mammals: (i) a group of extinct carnivores called hyaenodonts; two groups of rodents: (ii) anomalies (scaly tailed squirrels) and (iii) hystricognaths (a group that includes hairless porcupines and mole rats); and two groups of primates: (iv) strepsirrhines (lemurs and lorises) and (v) anthropoids (monkeys and monkeys).
By gathering data on hundreds of fossils from multiple sites in Africa, they were able to build evolutionary trees for these groups, identifying when new lineages branched out and time stamping the first and last known occurrence of each species. .
Their results show that all five groups of mammals suffered enormous losses around the Eocene-Oligocene boundary.
“It was a real reset button. After a few million years, these groups start to reappear in the fossil record, but with a new look, ”said Dr de Vries.
“The fossil species that reappear later in the Oligocene, after the great extinction event, are not the same as those found before.”
“It is very clear that there was a huge extinction event and then a recovery period,” said Dr. Steven Heritage, a researcher at Stony Brook University and the Duke Lemur Center Museum of Natural History.
The proof is in the teeth of these animals. Molars can say a lot about what a mammal eats, which in turn says a lot about its environment.
Rodents and primates reappeared after a few million years had different teeth. These were new species, which ate different things and had different habitats.
“We are seeing a huge loss of tooth diversity and then a period of recovery with new tooth shapes and new adaptations,” said Dr de Vries.
“Extinction is interesting that way. It kills things, but it also opens up new ecological opportunities for the lineages that survive in this new world, ”said Dr Matt Borths, curator of the Duke Lemur Center Museum of Natural History.
This decline in diversity followed by an upturn confirms that the Eocene-Oligocene border acted as an evolutionary bottleneck: most lineages became extinct, but a few survived.
Over the millions of years that followed, these surviving lineages diversified.
“In our anthropoid ancestors, diversity reached almost nothing about 30 million years ago, leaving them with just one type of tooth,” said Professor Erik Seiffert, a researcher at the Keck School of Medicine at the University of Southern California, the Duke Lemur. Center Museum of Natural History and the Los Angeles County Natural History Museum’s Department of Mammalogy.
“This ancestral tooth shape determined what was possible in terms of subsequent dietary diversification.”
“There is an interesting story about the role of this bottleneck in our own early evolutionary history.”
“We almost never existed, if our ape-like ancestors had become extinct 30 million years ago. Fortunately, they didn’t.
The study was published in the journal Communications biology.
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D. de Vries et al. 2021. Widespread loss of mammalian lineage and dietary diversity at the start of the Afro-Arab Oligocene. Common Biol 4, 1172; doi: 10.1038 / s42003-021-02707-9
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