Arctic Science Journeys

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More About Desmostylians
Charles Repenning
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desmostylian skeleton

A skeleton of a desmostylian named Paleoparadoxia that was collected in 1965 on the Stanford University, California, campus. This is the best and most complete skeleton of a desmostylian known from the New World.

In this view, the skeleton of Paleoparadoxia would not have looked different from that of Desmostylus, the difference being primarily in the structure of the teeth. This specimen is about 10 feet long (nose to rump). I drew the picture, after preparation of the skeleton, in about 1966 while an employee of United States Geological Survey, so it has no copyright restrictions.
 

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It seems natural to think that, because it had four legs, Desmostylus must have walked on land. But a great amount of debate has ensued over how this might have been done. The limbs are peculiarly constructed, which would have made walking on land very awkward. But the debate is entirely rhetorical, as no specimen has ever been found in non-marine deposits, so that it cannot be said that they did walk on land. It is my guess that it must have walked on land much as sea lions do today.

The desmostylians are known from about 30 million years ago until about 10 million years ago and entirely from the North Pacific Ocean. They presumably ate sea grass, which became rare with the development of kelp in the North Pacific. They did not seem to adapt to the change in diet from sea grass to kelp, as did the sea cows, the last of which were apparently killed by the Georg Wilhelm Steller expedition party in Alaska's Aleutian Islands in the 1700s.

The elephants, the sea cows, and the desmostylians are all believed to have derived from a hippopotamus-like thing called Moeritherium that lived in North Africa more than 40 million years ago. The intermediate forms are pretty well known between this ancestor and the elephants and the sea cows, but there is a gap missing between the ancestral form and the desmostylians.

Nevertheless the similarities between this ancestor and the earliest desmostylians are strong and the ancestry is believable.

In Alaska desmostylians have been found on Unalaska Island, on the Alaskan Peninsula, and on Kodiak Island. There are at least four genera included in the desmostylians. The genus Cornwallius was found on Unalaska, and the genus Desmostylia has been found on the Peninsula. The specimen found recently on Kodiak Island could be from either genus.

Dr. Charles Repenning
Denver Museum of Natural History


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