A fossil stored in the Smithsonian Institution’s National Museum of Natural History for several decades has been identified as a new species of ancient dolphin which would have lived in subarctic marine waters 24-29 million years ago.
Artistic reconstruction of a pod of Arktocara yakataga, swimming offshore of Alaska during the Oligocene, about 25 million years ago, with early mountains of Southeast Alaska in the background. Image credit: Alexandra Boersma.
The fossil in question is a partial skull about 9 inches (23 cm) long. It was found in southeastern Alaska in 1951 by U.S. Geological Survey geologist Donald J. Miller, and then spent decades in the Smithsonian’s collection.
It was analyzed by Smithsonian Institution researchers Nicholas Pyenson and Alexandra Boersma, who described it as a new genus and species and named it Arktocara yakataga.
By studying the skull and comparing it to those of other dolphins, both living and extinct, the team determined that Arktocara yakataga is a relative of the South Asian river dolphin (Platanista gangetica), which is the sole surviving species of a once large and diverse group of dolphins.
The skull, which is among the oldest fossils ever found from that group, called Platanistoidea, confirms that the South Asian river dolphin belongs to one of the oldest lineages of toothed whales still alive today.
The skull of Akrtocara yakataga rests on an 1875 ethnographic map of Alaska drawn by William Healey Dall, a broadly trained naturalist who worked for several US government agencies, including the Smithsonian, and honored with several species of living mammals. Image credit: James Di Loreto / Smithsonian Institution.
The South Asian river dolphin – a species that includes both the Ganges river dolphin and the Indus river dolphin – is of great interest to scientists.
It is an unusual creature that swims on its side, cannot see and uses echolocation to navigate murky rivers in Nepal, India, Bangladesh and Pakistan. Unlike its known ancestors, it lives only in fresh water.
“Today, Platanista gangetica is distributed in two subspecies across the Indus, Ganges-Brahmaputra-Megna and Karnaphuli-Sangu river systems of Southeast Asia, and remains highly threatened by human activities, including by-catch, fishing, and habitat modification,” the scientists explained.
“One of the most useful ways we can study Platanista is by studying its evolutionary history, by looking at fossils that are related to it to try to get a better sense of where it’s coming from,” Dr. Boersma added.
The paleontologists estimate that the Arktocara yakataga fossil comes from the late Oligocene epoch, around the time ancient whales diversified into two groups: baleen and toothed whales.
Fossils from Platanista gangetica’s now extinct relatives have been found in marine deposits around the world, but the Arktocara yakataga fossil is the northernmost find to date.
“Considering the only living dolphin in this group is restricted to freshwater systems in Southeast Asia, to find a relative that was all the way up in Alaska 25 million years ago was kind of mind-boggling,” Dr. Boersma said.
Research describing Arktocara yakataga is published online in the journal PeerJ.
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Boersma A.T. & Pyenson N.D. 2016. Arktocara yakataga, a new fossil odontocete (Mammalia, Cetacea) from the Oligocene of Alaska and the antiquity of Platanistoidea. PeerJ 4: e2321; doi: 10.7717/peerj.2321
