Researchers have unearthed a 36.4-million-year-old whale fossil in southern Peru. They found that the whale had teeth instead of baleen (keratin fibers) found in modern mysticetes. This suggests that prior to losing their teeth baleen whales were suction feeders which plunged down and sucked prey into their huge mouths.
The paleontologists have named it as Mystacodon, meaning "toothed mysticete." These most probably represent an intermediate step between raptorial and filter-feeding, filling a major gap in the history of the group.
The researchers believe that Mystacodon may have begun suction feeding as a response to ecological changes. To know the extent of adaptation of Mystacodon to bottom feeding, the researchers will investigate the bone compactness which will be more in slow-swimming animals living close to the sea floor.
Another surprising feature of Mystacodon is its pelvis which is fully articulated, tiny vestigial hind limbs which would have protruded away from the whale's body. Earlier, it was thought that whales lost the hip articulation before the divergence of baleen whales and modern toothed whales. The articulation of Mystacodon with the pelvis suggests that modern toothed whales and mysticetes may have independently lost this feature.