Mammals of the early Arikareean (“middle” Oligocene) Jones Branch Local Fauna, southeastern Mississippi, USA, with notes on two older taxa from the state and the timing of Midcontinent–Gulf Coastal Plain biotic disparity

Abstract A recently discovered site in southern Mississippi considered early Arikareean based on identified mammals represents the first of this age from the Gulf Coastal Plain outside of Florida. The Jones Branch Local Fauna was recovered from deltaic/estuarine deposits low in the Catahoula Formation resting unconformably on marl/clay beds of the subjacent, upper Rupelian (lower Oligocene), marine Paynes Hammock Formation. In addition to well-preserved plant material plus reptiles, amphibians, and fishes, the mammals are represented primarily by species previously known almost exclusively from the Great Plains, the northern Rocky Mountains (Montana), and/or John Day region, Oregon, with only a few apparently endemic to the Gulf Coastal Plain. Genera representative of the former include the proscalopid Mesoscalops , the sciurid Hesperopetes , the aplodontiid Downsimus , the putative early castoroid Eutypomys , the castorid Microtheriomys , the eomyids Apeomys and Leptodontomys , the florentiamyid Kirkomys , the mustelids Corumictis and Promartes , the tapir Protapirus , the leptochoerid Leptochoerus , the anthracothere Elomeryx , and the hornless ruminants Hypertragulus and ? Leptomeryx. Mesoscalops , Downsimus , and Apeomys are represented by new species. Additionally, a new genus and species of lagomorph is described, Oligolagus welleri , as is a new genus and new species of eomyid, Paraktioeomys palmeri. Known from both regions is the marsupial Herpetotherium , an apatemyid provisionally referred to Sinclairella , and the borophagine Phlaocyon. Gulf Coastal Plain endemics include the protoceratid Prosynthetoceras orthrionanus and apparently Oligolagus n. gen. and Paraktioeomys n. gen. The geographically broadly distributed horse Miohippus , rhinoceros Diceratherium , and giant entelodont Daeodon are also present. Marine mammals are represented by the dugong Crenatosiren olseni and the odontocete Agorophius pygmaeus. Additionally noted are two taxa from stratigraphically lower formations that are not part of the Jones Branch LF. These include a large species of the entelodont Archaeotherium and the anthracothere Elomeryx armatus , both of which were previously unknown along the Gulf Coastal Plain. The long recognized biotic disparity between the Midcontinent and Gulf Coastal Plain by the early Miocene was not yet strongly apparent during the early to middle Oligocene. UUID: http://zoobank.org/c1b57f31-4ed1-42fb-bf31-c803e2e61cfd