The oldest fossil musk turtles, genus Sternotherus, are reported from the Hemphillian of eastern Tennessee and central Florida. Sternotherus palaeodorus, n. sp., is known from five partial shells discovered at the late Miocene—early Pliocene (7–4.5 Ma; late Hemphillian) Gray Fossil Site in Washington County, Tennessee. Sternotherus palaeodorus possesses an enlarged intergular scute, wide first vertebral scute that overlaps peripheral set 1, posteriorly extensive hypoplastron to peripheral 7 contact, and a posteriorly situated inguinal musk duct pore (characteristics more typically seen in Kinosternon). A cladistic analysis recovered S. palaeodorus within crown group Sternotherus in the strict consensus and on the stem of Sternotherus in the majority rule consensus. Sternotherus bonevalleyensis, n. sp., from the Palmetto Fauna (5.5–5 Ma; late Hemphillian) of central Florida was perhaps contemporaneous with S. palaeodorus and is known only from isolated shell fragments. It is morphologically most similar to the Sternotherus minor complex and Sternotherus depressus. Subsequent Blancan fossils from the Suwannee River of Florida represent aff. S. minor peltifer. Additionally, a fragmentary left hyoplastron of cf. Sternotherus from Haile 19A, Alachua County, Florida, could be the oldest record for the genus (ca. 9–8.5 Ma; early Hemphillian). These accounts reveal that Sternotherus was diverse and moderately well distributed geographically by its first known fossil occurrences and support previous hypotheses that the Sternotherus minor complex evolved in the Gulf coastal plain and dispersed throughout that region since at least the latest Miocene-earliest Pliocene.
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