Fossil Sirenians and Desmostylids from Florida and Elsewhere

Abstract

Florida is the only part of the world in which extensive sirenian remains have been recovered from each epoch, beginning with the Eocene and continuing into the Recent. The evolutionary stage of the Mio-Pliocene sirenians from Florida parallels that of similarly aged European sirenians, in which a puzzling complex of specimens assigned to Metaxytherium, Halianassa, and Felsinothefium exists. From this study a proposal for synonymy of the above genera into the genus Metaxytherium is made. Florida metaxytheres are subdivided into three species with retention of trivial names now in use. Amplification and clarification of these species are made through a description of a number of new specimens. Changes in interpretation of the cranial morphology of Hesperosiren are suggested, with the result that this form appears to be closely related to Metaxytherium, rather than the highly aberrant form it has been considered. The presence of Halitherium in continental North America is now established beyond question in the new species H. olseni from Florida. Although of a similar evolutionary stage, this specimen is from beds of Middle to Upper Miocene, as compared to the Middle to Upper Oligocene European Halitherium. Ribs of Middle Eocene sirenians have been substantiated from a number of Florida localities, but no diagnostic elements have been found. Comments are made on Sirenia from areas other than Florida. These include a review of Sirenia from Java, the second report of a dugongid from South America, the validity of the Argentine trichechid Ribodon, and a report on the nomenclatorial status of Manatus and Trichechus. Desmostylid remains have been authenticated only from the circum-North Pacifc region, but reports on fragmentary teeth, incorrectly identified, have been attributed to Desmostylus from various localities. Two such proposals, Cryptomastodon from Java and Desmostylus from Texas, are discussed. Reports on new specimens of Cornwallius from the Aleutian chain, and Desmostylus from California and Florida are made, the latter being the first desmostylid authenticated outside of the Pacific. Discovery of Desmostylus in Florida extends its upper stratigraphic range from Late Miocene to Mio-Pliocene or to Middle Pliocene (Hemphillian), according to the age designation given to the Bone Valley Formation.