squalodon

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Squalodon.
This was a 10ft long toothed whale that lived during the Oligocene epoch. Its name means “shark tooth”, obviously describing the incredibly shark-like nature of its rear teeth, most notably the flat and serrated shape. No modern whales have dentition like this- all toothed whales have conical teeth that are usually blunted from use, as did most Oligocene-Holocene whales. Their ancestors, however, had the same shark-like teeth. Its front teeth were typically conical and long, overlapping towards the end of its snout, which is unusual in that Squalodon should retain ancestral teeth whilst still developing modern teeth.

Similarly, their necks were very mobile, much like extant beluga whales. Archaic whales typically had more mobile necks than the other whales that were evolving at the same time as Squalodon.

Their skulls possessed signs of the first development of echolocation.