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An international team of researchers has used advanced DNA sequencing methods to retrieve and analyze mitochondrial genome data from two lineages of saber-toothed cats, Smilodon and Homotherium. Published in the journal Current Biology, the results suggest that these iconic felids diverged from each other about 18 million years ago and shared a common ancestor with all living cat-like species about 20 million years ago.
Smilodon populator. Image credit: Rom-diz / CC BY-SA 3.0.
“It’s quite crazy that, in terms of their mitochondrial DNA (mtDNA), these two saber-toothed cats are more distant from each other than tigers are from house cats,” said lead author Dr. Johanna Paijmans, from the University of Potsdam in Germany.
Dr. Paijmans and co-authors reconstructed the mitochondrial genomes from ancient-DNA samples representing three Homotherium from Europe and North America and one specimen of Smilodon populator.
The Smilodon sample was collected in Chile and is dated to 11,335 years. Two Homotherium fossils were collected in northwest Canada. The European Homotherium was recovered from the North Sea and is dated to 28,000 years.
“One of the Homotherium specimens under investigation is a unique fossil: a 28,000-year-old mandible recovered from the North Sea,” Dr. Paijmans said.
“This find was so special because Homotherium is generally believed to have gone extinct in Europe around 300,000 years ago, so this specimen is over 200,000 years younger than the next-to-youngest Homotherium find in Europe.”
The new DNA evidence confirmed that this surprisingly young specimen did indeed belong to a Homotherium.
The discovery suggests that the saber-toothed cats continued to live in Europe much more recently than paleontologists previously thought.
Time-calibrated mitochondrial phylogeny of the Felidae, including the saber-toothed cat Smilodon and scimitar-toothed Homotherium. Image credit: Paijmans et al, doi: 10.1016/j.cub.2017.09.033.
“Mitochondrial DNA that we recovered from the North Sea Homotherium specimen confirms the Late Pleistocene survival of this enigmatic saber-toothed cat in Eurasia,” Dr. Paijmans and colleagues said.
“Much like Denisovan hominins, the North Sea Homotherium represents another striking example of the major gaps in our knowledge of Pleistocene fauna composition on the Eurasian continent and holds important clues about population and extinction dynamics of Pleistocene species.”
“We also found a deep divergence between Smilodon and Homotherium (18 million years), but limited diversity between the American and European Homotherium specimens,” the scientists said.
“The genetic data support the hypothesis that all Late Pleistocene Homotherium should be considered a single species, Homotherium latidens, which was previously proposed based on morphological data.”
“This study highlights the importance of combining morphological and genetic information for species identification,” they concluded.
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Johanna L.A. Paijmans et al. Evolutionary History of Saber-Toothed Cats Based on Ancient Mitogenomics. Current Biology, published online October 19, 2017; doi: 10.1016/j.cub.2017.09.033
