Equus from Leisey Shell Pit 1A and other Irvingtonian localities from Florida

Abstract

Three species of Equus (informally designated Equus sp. A, Equus sp. B, and Equus sp. C) are recognized from the Irvingtonian (latest Pliocene-middle Pleistocene) of Florida. The most widespread and abundant of the three, Equus sp. A. resembles E. scotti and E. conversidens in most characters but is intermediate in size between these two species. It may represent a geographic variant of either of these or a distinct species. The types of E. leidyi and E. littoralis fall within the observed range of morphological variation and size in the abundant Leisey Shell Pit `1A sample of Equus sp. A. Equus sp. B, recognized primarily from the Leisey 1A locality, is a moderate-sized member of the subgenus E. (Hemionus) based on its slender metapodials and cheektooth morphology, and probably represents an undescribed species. Dental and metapodial characters and size distinguish Equus sp. B from the three other recognized North Amencan species of E. (Hemionus), E. calobatus, E. francisci, and E. pseudaltidens. The latter is proposed as a replacement species name for E. altidens (Quinn), which is a junior homonym of E. altidens von Reichenau. Equus sp. C, the rarest species of the three, is found only at Haile 16A and Leisey 1A. It is a large species with complex fossette plications, deep molar ectoflexids, and compressed lower incisors that lack or have poorly developed infundibula. Previously, Cope and Hay described similar material from Florida as E. fraternus, a name of questionable validity. The phylogenetic relationships of Equus sp. C with other members of the genus are uncertain pending recovery of cranial material, but a close relationship with E. (Amerhippus) is possible.