Elephant Family Tree Needs a Rewrite

According to new research published in the journal eLife, the straight-tusked elephant (Palaeoloxodon antiquus), a species of giant elephant that lived 1.5 million to 100,000 years ago, is more closely related to the extant African forest elephant (Loxodonta cyclotis) than the forest elephant is to its nearest living relative, the African savanna elephant (Loxodonta africana).

Straight-tusked elephants (Palaeoloxodon antiquus). Image credit: Apotea / CC BY-SA 3.0.

The study challenges a long-held assumption among paleontologists that Palaeoloxodon antiquus was most closely related to the Asian elephant (Elephas maximus). The findings also add to the evidence that today’s African elephants are two separate species, not one, as was once assumed.

“Palaeoloxodon antiquus males stood up to 4 m tall and weighed as much as 13 tons, more than twice the weight of today’s largest elephants. Understanding their genetic heritage is key to keeping today’s elephants from going extinct,” said study co-author Dr. Alfred Roca, from the University of Illinois at Urbana-Champaign.

For the study, Dr. Roca and his colleagues sequenced full mitochondrial genomes from four and partial nuclear genomes from two Palaeoloxodon antiquus fossils.

These fossils were collected at two sites in Germany, Neumark-Nord and Weimar-Ehringsdorf, and date to interglacial periods 120,000 and 244,000 years ago, respectively.

The sequences were analyzed to determine how straight-tusked elephants are related to the three living elephant species and the extinct mammoth.

“Up until now, genetic research on bones that are hundreds of thousands of years old has almost exclusively relied on fossils collected in permafrost,” said lead co-author Dr. Matthias Meyer, a researcher from the Max Planck Institute for Evolutionary Anthropology.

“It is encouraging to see that recent advances in laboratory methods are now enabling us to recover very old DNA sequences also from warmer places, where DNA degrades at a much faster rate.”

A study by Meyer et al reconfigures the elephant family tree, placing the straight-tusked elephant (Palaeoloxodon antiquus) closer to the African forest elephant (Loxodonta cyclotis), than to the Asian elephant (Elephas maximus), which was once thought to be its closest living relative. Image credit: Asier Larramendi Eskorza / Julie McMahon.

The mitochondrial analysis revealed that a shared ancestor of Palaeoloxodon antiquus and the African forest elephant lived sometime between 1.5 million and 3.5 million years ago.

Their closest shared ancestor with the African savanna elephant lived between 3.9 and 7 million years ago.

According to the team, the nuclear DNA told the same story.

“From the study of bone morphology, people thought Palaeoloxodon antiquus was closer to the Asian elephant. But from the molecular data, we found they are much closer to the African forest elephant,” said co-author Dr. Yasuko Ishida, from the University of Illinois at Urbana-Champaign.

“Palaeoloxodon antiquus is a sister to the African forest elephant; it is not a sister to the Asian elephant or the African savanna elephant,” Dr. Roca said.

“Paleogenomics has already revolutionized our view of human evolution, and now the same is happening for other mammalian groups,” said lead co-author Prof. Michael Hofreiter, from the University of Potsdam.

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Matthias Meyer et al. 2017. Palaeogenomes of Eurasian straight-tusked elephants challenge the current view of elephant evolution. eLife 6: e25413; doi: 10.7554/eLife.25413