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New work supports Charles Darwin's speculation in The Origin of Species that some of the earliest baleen whales may have been suction feeders, and that their mud grubbing served as a precursor to the filter feeding of today's giants of the deep. Mammalodon colliveri, a primitive toothed baleen whale from the Oligocene, may have used its tongue and short, blunt snout to suck small prey from sand and mud on the seafloor
Although Mammalodon had a total body length of about 3 m, it was a bizarre early offshoot from the lineage leading to the 30 metre long blue whale. The new research shows that Mammalodon is a dwarf, having evolved into a relatively tiny form from larger ancestors. link