A fossil trionychid turtle from the early tertiary Chuckanut Formation of Northwestern Washington
Mustoe, George E.
Girouard, Samuel-P, Jr
MetadataShow full item record
Washington's vertebrate fossil record is so sparse that every discovery deserves careful scrutiny. A fossilized turtle carapace found in 1960 in fluviatile sandstone of the Chuckanut Formation of western Whatcom County was originally identified as a member of the Testudinoidea superfamily, and an adjacent bone fragment was considered to be evidence of some larger animal. Re-examination indicates that the carapace represents a member of the Trionychidae (soft-shelled turtles). Computerized axial tomography suggests that the nearby bone probably came from the turtle. Trionychid fossils are abundant in early Tertiary rocks, but their remains have not been found in younger rocks in the northwest region. The only extant trionychid found west of the Mississippi is Trionyx spiniferus, which inhabits small areas of eastern Montana and the Colorado River region of the southwest. This restriction in geographic range probably resulted from global cooling that started in the late Eocene, and by habitat destruction caused by episodes of mountain building that began a few million years later