Fossil of oldest known baleen-whale relative unearthed in Peru

By Sarah McQuate

The discovery of a whale fossil dating back to 36.4 million years ago has filled in a gaping hole in the evolution of baleen whales, a group that includes humpbacks (Megaptera novaeangliae) and blue whales (Balaenoptera musculus). The creature, named Mystacodon selenensis, is the oldest baleen-whale relative yet found.

The skeleton displays traits that place it firmly as the first baleen-whale relative known to emerge after an ancient group of whale ancestors called basilosaurids split into two: one branch led to the toothed whales, which include sperm whales (Physeter macrocephalus) and dolphins, and the other to baleen whales. Researchers reported their findings on 11 May in Current Biology1.

“This is the fossil that we’ve been waiting for,” says Nick Pyenson, a palaeontologist at the Smithsonian National Museum of Natural History in Washington DC. Whale fossils from this time period can answer a lot of questions that researchers have about the origins of living whale lineages, he says. They include the appearance of the earliest baleen whale ancestors.

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