A stratigraphically precise record of Protosiren (Protosirenidae, Sirenia) from North America
Abstract:A partial left innominate of a sirenian, mostly consisting of the ilium, was recently recovered from the late Middle Eocene (Bartonian) Cross Member of the Tupelo Bay Formation in Orangeburg County, South Carolina. It most closely resembles the innominate of Protosiren sattaensis Gingerich et al., 1995 from the Bartonian of Pakistan, though due to the present lack of knowledge of variation within the genus, it is best assigned to Protosiren sp. This specimen was collected from the same horizon as the holotype of Carolinacetus gingerichi, representing an unusual case of protosirenid and protocetid co-occurrence. This new material is the first Eocene sirenian material diagnosable to the genus level that came from unambiguous, age-restricted strata in North America. Previous reports of Eocene Sirenia from South Carolina have consisted of indeterminate rib fragments and a skullcap described by Sanders, all from approximately Priabonian strata: the Pregnall Member of the Cross Formation or the Harleyville Formation. Recent geologic studies of the Castle Hayne Formation suggest that “Lutetian” Protosiren and dugongid material from North Carolina is instead Bartonian or Priabonian in age. Thus after presumably dispersing westward from North Africa, prorastomid sirenians in the Western Hemisphere first appear in Jamaica, protosirenids and/or dugongids on the Gulf Coast, and then protosirenids and dugongids later in the Carolinas. The Bartonian marks the beginning of the Middle Eocene Climatic Optimum, and this event may have aided the northward movement of sirenians in the Eocene.
Document Type: Research Article
Publication date: November 1, 2010
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