Species occurrences of Mio–Pliocene horses (Equidae) from Florida: sampling, ecology, or both?

During the late Miocene and early Pliocene (latest Hemphillian, Hh4 interval, 5.7 to 4.75 Myr) a distinctive suite of four species of extinct horses (Family Equidae) were widespread in North America. This includes Nannippus aztecus, Neohipparion eurystyle, Astrohippus stocki, and Dinohippus mexicanus. In Florida, two additional equid species, Pseudhipparion simpsoni and Cormohipparion emsliei are typically found at Hh4 localities. Here we compare horses from four Hh4 Florida fossil sites, including three from the Bone Valley mines, and a fourth from the recently discovered Montbrook site. Two of these have all six predicted species, one has five species, and one has only four species present. To explain these differences, we used species counts from research databases and rarefaction simulation to better understand the relative abundances, species richness, and occurrences of these horses from these four sites. The Palmetto Mine (Agrico) site, with five equid species, appears to lack th...