Hagerman Fossil Beds National Monument - Turtle (U.S. National Park Service)

NPS

Clemmys owyheensis, an extinct pond turtle

The Fossil Turtles of Hagerman: Just Shells of Their Former Selves

Idaho is not known for its turtles. In fact, many people may not be aware that there is even a turtle living in the state, the painted turtle, found only in the panhandle. Since there are no turtles living in any parts of the Snake River drainage today, it may be somewhat of a surprise to learn that pieces of turtle shell are one of the most common fossils found at Hagerman Fossil Beds and that two types of extinct fossil turtles have been found here.

Hagerman turtles were first described in 1933 by Charles W. Gilmore, a paleontologist at the Smithsonian, better known for his work on dinosaurs and fossil lizards. The specimen, a complete shell plus the skull and jaw and most of the limb bones, was found in 1930 during excavations at the Horse Quarry. To find a complete shell of a turtle is unusual in itself since the shell is composed of numerous distinct bones (about 59 depending on the species), which often separate after the animal dies, however, to find the other bones of the skeleton as well, is an extremely rare occurrence. Since most pieces of turtle found at the monument are individual bones of the shell, this animal must have been buried very quickly after its death before the bones could become scattered.

Gilmore described the animal as a new species of the pond turtle genus Pseudemys, Pseudemys idahoensis, although recent research places this animal in the genus Trachemys, the slider turtles. Only one species of Trachemys is present in the United States today, Trachemys scripta, better known as the red-eared or pond slider.

The living slider is found along the Atlantic Coast from Virginia to northern Florida and westward to southern Texas and northward to northern Kansas, Missouri and Illinois. Outside of the United States this species is known from Mexico, Central America and South America. Fossil specimens of Trachemys known from an equally wide range of localities and include Florida, Kansas and Texas as well as Idaho. It is very likely that Trachemys idahoensis is ancestral to the living Trachemys scripta.

NPS

Clemmys owyheensis Carapace Exterior

The second type of turtle found as a fossil at Hagerman is an extinct species of the Western Pond Turtle, Clemmys owyheensis. The living species of Clemmys, C. marmorata, lives along the Pacific Coast from southwestern British Colombia to northern Baja California with an eastern population in the Truckee and Carson Rivers of Nevada. The presence of the Nevada population between Hagerman and California is further evidence for the former drainage of the Snake River out of Lake Idaho across northern Nevada and into northern California.

The living species of both Trachemys and Clemmys are thoroughly aquatic turtles that seldom venture on land. That their close relatives are common as fossils at Hagerman fits our interpretation, suggested by many of the other animals such as beaver, muskrat, otter, frogs and the waterfowl, that 3.5 million years ago an extensive wetland habitat existed in the area. Their disappearance from southern Idaho probably resulted from the increasing drying and cooling of the region and loss of suitable habitat, possibly caused by the continued uplift of the Cascade Mountains and the resulting rain shadow in Idaho. Although not present in Idaho today, studies of their surviving descendants in other areas can provide us with an insight into what the environment was like in southern Idaho 3.5 million years ago.

NPS

Clemmys owyheensis Plastron Interior

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