Odobenocetops
Odobenocetops is an extinct genus of small toothed whale known from Chile and Peru. Its fossils are found in Miocene-aged marine strata of the Bahía Inglesa Formation and Pisco Formation. Two species of Odobenocetops are currently recognized, O. peruvianus and the slightly younger O. leptodon. Odobenocetops is mostly known for its large asymmetric tusks, which emerge from pronounced processes formed by the premaxillae, known as the alveolar sheaths. These tusks are thought to be sexually dimorphic and are only strongly pronounced in male individuals, while females appear to possess two similarly sized tusks. In the holotype of O. peruvianus the elongated right tusk is broken, leaving its precise length ambiguous. O. leptodon on the other hand preserves complete tusks, showing that at least in this species the longer tusk reached a total length of 1.35 metres long, 1.07 metres of which is located outside of the alveolar sheath. While these tusks are reminiscent of the tusk seen in the closely related narwhals, they evolved independently. Their purpose remains unknown, but the most common interpretation is that they served a non-violent social role, as they are too fragile for combat. The alveolar sheaths on the other hand may have been used as orientation guides during foraging. Besides the two tusks in the upper jaw, Odobenocetops is thought to have been toothless. Another difference between this genus and other whales is that the melon, an organ important for echolocation, is reduced in O. leptodon and vestigial or entirely absent in O. peruvianus. At least the older species compensated for this by having large, dorsally located eyes giving it binocular vision. The fact that only the older species lost its melon has been taken as evidence that they were sister taxa, rather than one species evolving directly from the other. In addition to their vision or echolocation, Christian de Muizon argues that they may have possessed tactile hair, which are also found in walrus and to a lesser extent in Amazon river dolphins. Odobenocetops is among the cetaceans with the greatest range of head motion, exceeding even the values of the beluga whale. This may have helped while foraging, extending the neck in a way that keeps their tusks roughly parallel to the rest of the body. Due to the anatomy of the palate and other similarities to the walrus, it is thought that this whale was a suctionfeeding molluscivore, searching for bivalves on the ocean floor, uncovering them with precise jets of water, grasping the uncovered molluscs with a powerful upper lip and using its tongue like a piston to suck out the soft parts of their prey, leaving the shell intact.
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