The desmostylians were a group of strange aquatic mammals that have been aptly described as "seahorses." About the size of a pony, and superficially similar in appearance, they lived along the coasts of the North Pacific in Miocene times, between about 25 and 5 million years ago. The single record of a fossil from coastal Florida suggests that desmostylians found their way from the Pacific into the Atlantic via the narrow seaway that separated North and South America until the Pliocene, about 5 million years ago. But the origin, relationships and diet of desmostylian remain a mystery.
name: Desmostylus time: Miocene locality: Asia (Japan) and North
America (Pacific coast) size: 6 ft/1.8 m long
Desmostylus was a typical member of the group. Built like a hippopotamus, and perhaps behaving like one too, it had a thickset body and stout legs with broad feet, each with 4 hooved toes. The bones of the lower foreleg were fused into a solid pillar, which meant that the foot could not be turned without turning the whole limb. Underwater, the animal probably poled itself along, in the same manner as a modern hippo "walks" over the riverbed. On land, Desmostylus must have been quite clumsy.
The front parts of both the upper and lower jaws were elongated and carried an array of forward-pointing tusks, formed by the elongated incisors and canines. The animal's head must have looked similar to that of some of the shovel-tusked elephants that lived at the time (see pp. 238-241). The unusual back teeth formed clusters of upright cylinders.
Desmostylus must have had an amphibious lifestyle, paddling around in the coastal shallows, prising shellfish off rocks with its front tusks. It may also have sunk to the seabed in search of food. Some paleontologists suggest that it grazed on the seaweeds between the tides.
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