New fossils of early toothed baleen whale provide insight into evolution of filter-feeding

A recent publication in the journal PeerJ has revealed an extensive collection of new fossils belonging to Coronodon, an early toothed baleen whale species from the Oligocene period (23-30 million years ago) found in rock layers near Charleston, South Carolina. The discovery includes five new skulls, representing two new species: Coronodon planifrons and Coronodon newtonorum, as well as juvenile specimens of Coronodon havensteini, which were initially named by the same team in 2017 based on a single skull. Coronodon is regarded as one of the earliest members of the group of baleen whales, and its name translates to “crown tooth” due to its large, multi-cusped teeth that overlap in the mouth.

The teeth of Coronodon have sparked a scientific debate over whether they were primarily used for cutting, filter-feeding, or a combination of both. The two newly discovered species, Coronodon planifrons and Coronodon newtonorum, were found in the same rock layer and dated back to the late Oligocene period (25-23 million years ago). Coronodon planifrons, named after a skull with a flat “forehead,” potentially had an extra tooth compared to other species. Meanwhile, Coronodon newtonorum had slightly smaller teeth and an unusual mouth shape that made it appear to be continuously smiling.

Newly found specimens of Coronodon havensteini include an old adult and two calves, providing a rare insight into the early growth and development of Oligocene whales. Unlike present-day dolphins and baleen whales, the snout of Coronodon remained the same length during growth, which is thought to be associated with its large teeth. These new discoveries suggest that Coronodon had a relatively large head compared to its skeleton, moved in a manner similar to modern baleen whales, and likely had a flexible chin and skull joints associated with filter-feeding. However, it did not have baleen. By reconstructing the evolutionary tree of baleen whales, scientists have placed Coronodon as the earliest branch, a significant finding for understanding the transition from tooth-based feeding to filter-feeding using baleen.

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