Giant Marmot

Modern Yellow-bellied Marmot

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Hagerman's Giant Marmot

Anyone traveling through southern Idaho has seen them by the side of the road, or often, running across the road playing "chicken" with your car. They are the largest living member of the squirrel family and are known locally as rockchucks, a western relative of the well known woodchuck or ground hog, who gets national attention every February 2. The rockchuck or yellow-bellied marmot, Marmota flaviventris, is found throughout the western United States and can be found in a variety of environments from desert to mountain.

 

Lower Marmot Jaw

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Many visitors to the area are amazed by the size of the largest of all ground squirrels, 3.9 kilograms (8.5 pounds) on the average although some individuals will get as large as 5.2 kg (11.5 pounds). Had people been visiting Hagerman Fossil Beds 3.5 million years ago they would have been even more amazed at the size of the fossil marmot, Paenemarmota barbouri, found here.

It was roughly twice the size of our living yellow-bellied marmot. The giant marmot was first described in 1948 based on a specimen found in Kansas. During the Pliocene, it was widely distributed in western North America and has also been found in Nebraska, Texas, Arizona and northern Mexico. It was not reported from Hagerman until 1969. The Hagerman record is currently the most northern and western record for the animal.

 

Marmot Jaw

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Most of the skeleton of Paenemarmota is unknown and just about all records of the animal are based on lower jaws and a few palates and partial skulls. There are probably lots of bones of Paenemarmota in museum collections, but they have not been recognized. It's not surprising since teeth, skulls and jaws are the most distinctive part of an animal and are the easiest to identify. After an animal dies, unless it is buried quickly, the bones will become separated and scattered once the muscles and ligaments decay. Unless the bones of the skeleton are associated with the skull or jaw a paleontologist might not be absolutely sure that they belong to the same type of animal. This is not a problem unique to Paenemarmota, but to all fossil vertebrates. Unless there is a complete skeleton found, it is difficult for a paleontologist to determine which bones belong together. Often in some cases the bones of different types of animals might be mixed together, or different names may be given to the same animal based on different parts of the skeleton. Both of these problems have happened in the past but as new and more complete specimens are found, paleontologists are constantly updating our understanding of each species. So who knows, there are probably lots of bones of this animal squirreled away in museum collections, just waiting to be recognized.

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This article originally appeared in The Fossil Record, Summer 1998