BULLETIN of the FLORIDA STATE MUSEUM Biological Sciences Volume 32 1988 Number 3 CALIPPUS AND PROTOHIPPUS (MAMMALIA, PERISSODACTYLA, EQUIDAE) FROM THE MIOCENE (BARSTOVIAN-EARLY HEMPHILLIAN OF THE THE GULF COASTAL PLAIN Richard C. Hulbert, Jr. FSM UNIVERSITY OF FLORIDA GAINESVILLE Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. OLIVER L. AusTIN, JR., Editor S. DAVIDWEBB, Associate Editor RHODA J. BRYANT, Managing Editor Consultants for this issue: RICHARD H. TEDFORD MICHAEL O. WOODBURNE Communications concerning purchase or exchange of the publications and all manuscripts should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of Florida; Gainesville FL 32611; U.S.A. This public document was promulgated at an annual cost of $4880.00 or $4.880 per copy. It makes available to libraries, scholars, and all interested persons the results of researches in the natural sciences, emphasizing the circum-Caribbean region. ISSN: 0071-6154 CODEN: BF 5BAS Publication date: January 21,1988 Price: $5.00 HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 221 CALIPPUS AND PROTOHIPPUS (MAMMALIA, PERISSODACTYLA, EQUIDAE) FROM THE MIOCENE (BARSTOVIAN-EARLY HEMPHILLIAN) OF THE GULF COASTAL PLAIN Richard C. Hulbert, Jr.* ABSTRACT Nine species of Calippus and four species of ProtohiDDus are recognized from the late Miocene (late Barstovian to early Hemphillian, from about 14.0 ma to 6.0 ma) of the Gulf Coastal Plain. nvo subgenera of Calipous are recognized: C. (Calippus) which includes four small species, C. proglacidus n. comb. (senior synonym of C. francisi), f. placidus, C. regulus and C. elachistus n. sp.; and C. (Grammohippus) n. subgen. which contains five medium-sized species: C. circulus n. comb., C. martini, C. cerasinus n. sp., C. hondurensis n. comb., and C. maccart¥i n. sp. Protohippus is a valid genus, not synonymous with nor related to Merychippus sensu stricto, and not ancestral to Pliohipous, Dinohippus, or Eg--us. Four successive species of Protohippus are recognized from the Gulf Coastal Plain, E. vetus, E. perditus, E. supremus (senior synonym of E. simus), and P. Ridlevi n. sp. Eight of these 13 species also ranged north into the Great Plains, and are useful in faunal and chronological correlations between the two regions. Phylogenetic analyses of cranial and dental characters suggest the following hypotheses: (1) Protohipous and Calippus are more closely related to each other than either is to any other equid genus, and the two form a monophyletic group, the Subtribe Protohippina Quinn new rank; (2) Protohippus and Calippus form the sister group to a second monophyletic radiation of hypsodont equids, the equines; and (3) the *The author is a Postdoctoral Research Fellow at the Florida State Museum, University of Florida, Gainesville FL 32611. HULBERT, R.C., JR. 1988. Calipous and Protohippus (Mammalia, Perissodactyla, Equidae) from the Miocene (Barstovian-Early Hemphillian) of the Gulf Coastal Plain. Bull. Florida State Mus., Biol. Sci. 32(3):221-340. 222 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) common ancestor shared by protohippines and equines was a relatively small, Iate Hemingfordian-early Barstovian taxon, dentally of primitive merychippine-grade. In these . clades, dental characters are more subject to parallelism than cranial characters, thus the latter arc often more useful for deducing phylogenetic relationships. RESUMEN Se reconocen nueve especies de Calippus y cuatro especies de Protohippus del Mioceno tardio (Barstoviano tardio hasta Hemphiliano temprano, de aprox. 14.0 ma a 6.0 ma) de la planicie costera deI Golfo de Mdxico. Se reconocen dos subg6neros de Calippus: C. (Calippus) incluyendo cuatro especies de tamafio pequeno, C proplacidus comb. n. (sin6nimo mayor de C. francisi), C placidus, C. reaulus, y C elachistus esp. n.; y C. (Grammohippus) subgdn. n. que incluye cinco especies de tamafio mediano: C. circulus comb. n., C. martini. C cerasinus esp. n., C hondurensis comb. n., y C. maccartyi esp. n. Protohippus es un gdnero vhlido; no es sin6nimo ni pariente cercano de Merychippus en el sentido estricto, ni es progenitor de Pliohippus, Dinohippus, ni Eouus. Cuatro especies sucesivas de Protohippus se reconocen de la planicie costera del golfo, 2 vetus, E. perditus, P. supremus (sin6nimo mayor de P. simus), y P. Ridlevi esp. n. Ocho de estas trece especies se extendian al norte hasta.los Ilanos centrales, y son utiles en correlaciones faunisticas y cronologicas entre las dos regiones. Andlisis filogen6ticos de caracteristicas craneales y dentales sugieren las siguientes hip6tesis: (1) Protohippus y Calippus son mas afines entre si que con cualquier otro gdnero Equido, y los dos forman un grupo monofildtico, la subtribu Protohippina Quinn, rango nuevo; (2) Protohippus y Calippus forman el grupo hermano a una segunda linea mondfilttica de Equidos hipsodontos, los equinos; y (3) el progenitor comfin de los protohipinos y equinos era un taxon de tamafio relativamente pequefio, del Hemingfordiano tardio o Barstoviano temprano, con dientes deI grado merychipino primitivo. En estas lineas filogendticas, las caracteristicas dentales son Inds sujetas a paralelismo que las caracteristicas craneales; por eso las ultimas son frecuentemente mds 6tiles para deducir relaciones filogendticas HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 223 TABLE OF CONTENTS INTRODUCTION 223 ACKNOWLEDGEMENTS 225 ; ABBREVIATIONS 225 MATERIALS AND METHODS 228 SYSTEMATIC PALEONTOLOGY 231 Calippus 231 Calippus proplacidus n. comb. 235 Calippus placidus 243 Calippus regulus 246 Calippus sp 249 Calippus elachistus n. sp 249 Grammohippus n. subgon 254 Calippus circulus n. comb. 256 Calippus martini 259 Calipous cerasinus n. sp. 264 Calippus hondurensis n. rnmh 271 Calippus sp., cf. C hondurensis 275 Calippus maccartvi n. sp. 276 Protohippus 281 Protohippus perditus 282 Protohippus supremus 286 Protohippus gidleyi n. sp 294 PHYLOGENY OF CALIPPUS AND PROTOHIPPUS, AND THEIR RELATIONSHIPS WITH OTHER EQUID GENERA ...................... 301 DWARFING EQUID LINEAGES AND CALIPPUS 309 BIOCHRONOLOGY AND BIOGEOGRAPHY 310 SUMMARY 311 REFERENCES... 214 TART FS 319 INTRODUCTION This is one of several recently completed studies describing fossil equids from the Late Neogene (Barstovian, Clarendonian, and Hemphillian Land Mammal Ages) of the Gulf Coastal Plain of North America. Previous studies have dealt with Dinohippus and Astrohippus (MacFadden 1986), Pseudhipparion (Webb and Hulbert 1986), Neohippadon (Hulbert 1987b), Comiohipparion and Hipparion (Hulbert 1987c; Hulbert in press), and 224 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) Nannippus (Hulbert 1987a; in prep. A). Together they provide modern revisions of these taxa from this important faunal province, aid in intracontinental biostratigraphic correlation of Gulf Coastal Plain faunas with radiometrically dated faunas from the western United States, and allow greater understanding of equid evolution and paleoecology during a critical period of their history in North America Protohippus was first described by Leidy ( 1858) as a subgenus of Equus, but was later given generic status (Leidy 1869). The taxon was widely used until about 1930, with many species referred to it (see e.g. Gidley 1907). McGrew and Meade (1938), and later Stirton (1940), reduced it to the rank of subgenus, within an expanded, horizontal concept of Merychippus. in their revised cl assification of the Equidae, M. (Protohippus) was considered ancestral to all equine genera, just as M. (Megchippus) was thought to give rise (paraphyletically) to all hipparionines. It will be shown that this classification, which relied primarily on upper cheektooth morphology, is incorrect, based on a phylogenetic analysis that additionally includes cranial, incisor, and lower cheektooth characters. However, much of the classification of Gidley (1907) is not falsified by this analysis. Calippus was first described by Matthew and Stirton (1930) as a subgenus of Protoh*pits, but was later considered a distinct genus by Stirton (1935; 1940) and subsequent authors. Cal*pits has often been thought to consist solely of dwarf species of equines, somewhat analogous to the position of Nannippits among hipparionines (Stirton 1940; Simpson 1951). Originally, however, Stirton and co-workers included larger species in Cal»us (e.g. C. mamni and C. ansae; Stirton 1935; Hesse 1936), a concept Stirton later abandoned. Study of previously undescribed specimens in the Frick Collection of the American Museum of Natural History, including complete skulls and mandibles of most species, indicates that Calippus is indeed a distinct genus characterized by several unique autapomorphies, that it includes both small and moderate-sized species, and that it is more closely related to Protohippus than any other equid genus. The purpose of this study is to document the systematics and biochronology of Gulf Coastal Plain Calippus and Protoh*pus, including the recognition of four new species. A second study (Hulbert in prep. B) will examine populations from the Great Plains, and will include detailed descriptions of relatively complete cranial material collected by Morris Skinner and others for Childs Frick (and now housed in the AMNH). Some preliminary discussion of Great Plains material in this report is unavoidable, because: (1) some species are poorly known in the literature, and any referral to them must be justified by reference to types, topotypes, or specimens from near the type locality; (2) some populations from the Gulf Coastal Plain are referable to described Great Plains taxa, but these species need to be transferred to Calippus or Protohippus from another genus; or (3) specimens HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 225 of previously undescribed taxa are known from both geographic provinces, and because of better quality, that from the Great Plains is chosen to be the type, or contributes characters not observed in Gulf Coastal Plain material. ACKNOWLEDGEMENTS The following individuals and institutions allowed me access and permission to study their collections during the course of this study: R. H. Tedford and M. J. Novacek, AMNH; E. L. Lundelius and W. A. Langston, TMM; R. M. Hunt and M. R Voorhies, UNSM; C. E. Ray, USNM; G. E. Schultz, PPM; J. H. Hutchison, UCMP; and D. P. Whistler, LACM. Jack Wilson (TMM) was a helpful source of information about Texas GuIf Coast biostratigraphy. Ron and Pat Love and Jim Shimfessel graciously notified the FSM of fossils discovered on their respective properties, and allowed museum field crews to.excavate additional specimens. Specimens used in this study were donated to the Florida State Museum by Rick Carter, Donald Crissinger, John Waldrop, Frank Garcia, James Ranson, Jeffrey Walker, Robert Summers, Steve Everett, George Heslep and Joe Larned. Figures 6, 11-12, 15A-15B, 156- 15H, 17-22, and 24- 25 were skillfully drawn by Wendy Zonilefer; Figures 5, 9, 13-14, and 15C- 15F by Gerald Masters; and Figures 4 and 23 by staff artists of the AMNH and used with the permission of R. Tedford. Earlier versions of this study were critically read by S. David Webb, Bruce MacFadden, R.H. Tedford, and M.O. Woodburne. Other input was provided by Gary Morgan, Ann Pratt, Steve Emslie and David Wright. The Love Site, which forms the core of my research of late Miocene equids from Florida, was excavated and curated with the support of NSF grants to Drs. Webb and MacFadden. Support for this study was provided by a research assistantship from the Department of Zoology, University of Florida, and from NSF Grant BSR-8515003 to Dr. MacFadden. This is University of Florida Contribution to Paleobiology No. 253. ABBREVIATIONS AMNH - Department of Vertebrate Paleontology, American Museum of Natural History, New York. ANSP - Academy of Natural Sciences, Philadelphia. F:AM - Frick Collection, housed with AMNH collection. MHNES - Museo de Historia Natural de El Salvador. PPM - Panhandle-Plains Historical Museum, Canyon, Texas. TAMU - Texas A&M University collection, now housed with TMM collection. TMM - Texas Memorial Museum, University of Texas, Austin. UCMP - University of California Museum of Paleontology, Berkeley. 226 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) UF - Vertebrate Paleontology Collection, Florida State Museum, University of Florida, Gainesville. UF/FGS - Florida Geological Survey Collection, now housed with UF collection. UNSM - University of Nebraska State Museum, Lincoln. USNM - National Museum of Natural History, Smithsonian Institution, Washington, D.C. WM - Walker Museum Collection, now housed at the Field Museum of Natural History, Chicago. WT - West Texas State University Collection, housed in the PPM. R, L - right, left. I/i - upper/lower incisor. C/c - upper/lower canine. P* - upper/lower premolar (e.g. P4 is an upper fourth premolar). M/m - upper/lower molar (e.g. m2 is a lower second molar). D/d - upper/lower deciduous tooth (e.g. dp2 is a deciduous lower second premolar). P34, p34, DP34, dp34, M12, m12 - collective terms for indistinguishable isolated teeth (e.g. P34 refers to upper third and fourth premolars). DPOF - dorsal preorbital fossa (= lacrimal or nasomaxillary fossa). assoc. - associated. s.s. - sensu stricto. s.1.- sensu lato. 1.f. - local fauna. ma - mega-anna, millions of years before present on the radioisotopic timescale. FL - Florida. NE - Nebraska. TX - Texas. x - sample mean. s - sample standard deviation. n - sample size. F - sample coefficient bf variation. OR - observed range of a sample. Abbreviations of dental measurements. Those in uppercase refer to upper dentitions; lowercase to lowers (measurements taken on occlusal surfaces are illustrated in Fig. 1). APL - maximum anteroposterior length, excluding the ectoloph and hypocone. BAPL - anteroposterior length at the base of the crown. TRW - transverse Width from mesostyle to lingual-most part of the protocone. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 227 5 12 A--1 --0 A 4. 13 1410 B i kiwn r- 1117 / 7-\--\ "3 44 15 j ~16 9 *- 3 -3\ :1: 19 12 DC H le I I / ? 7 ANTi~94--754 IF;~~12 T 13 tN,/~-5 ~-p--- ~ 16 4 3 1415 8 Figure 1. Schematic occlusal views of upper and Iower cheekteeth of equids demonstrating nomenclature and measurements used in this study. A. Upper left second premolar (anterior to left, labial up): 1, anterostyle (found on P2s and DP2s only); 2, hypoconal groove; 3, hypocone; 4, parastyle; 5, mesostyle; 6, metastyle; 7, pli caballin; 8, pli hypostyle; 9, pIi postfossette; 10, pli prefossette; 11, pli protoloph; 12, postfosette; 13, prefossette; 14, prefossette loop; 15, preprotoconal groove; 16, protocone; 17, protoselene. B. Upper right third or fourth premolar (P34) showing the four measurements taken on the occlusal surface of upper cheekteeth: 1, APL, maximum anteroposterior length, excluding the ectoloph and hypocone; 2, TRW, transverse width from mesostyle to lingual-most part of protocone; 3, PRL, maximum protocone length, excluding spur or connections to protoselene or hypocone (if present); 4, PRW, protocone width perpendicular to PRL. C. Lower left molar (m12, anterior to left, lingual up): 1, antisthmus; 2, ectonexid; 3, ectostylid (generally found only on deciduous premolars); 4, entoconid; 5, entoflexid; 6, hypoconid; 7, hypoconulid; 9, linguaflexid; 10, metaconid; 11, metaflexid; 12, metastylid; 13, paralophid; 14, pli caballinid; 15, postisthmus; 16, protoconid; 17, protostylid. D. Lower right third or fourth premolar (p34) showing the five measurements taken on the occlusal surface of Iower cheekteeth: 1, apl, maximum anteroposterior length, excluding protostylid; 2, atw, anterior width from metaconid to protoconid; 3, ptw, posterior width from metastylid to hypoconid; 4, mml, metaconid- metastylid length; 5, entl, length of entoftexid; 8, isthmus, the combined antisthmus and postisthmus when the ectoflexid is shallow. 228 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) PRL - maximum length of the protocone, excluding spur and connection to protoselene. PRW - maximum width of the protocone perpendicular to PRI. MSCH - crown height measured from the occlusal surface to the base of the crown along the mesostyle. UTRL - upper toothrow length from the anterior-most projection of the P2 to the posterior-most part of the M3. UDL - upper postcanine diastema length, measured between the alveoli of the C and the P2 (excludes DPl if present). ROC - radius of curvature of the mesostyle. apl - maximum anteroposterior length from the paralophid to the hypoconulid. bapl - anteroposterior length at the base of the crown. atw - transverse width from the protoconid to the metaconid. ptw - transverse width from the hypoconid to the metastylid. entl - anteroposterior length of the entoflexid. mm1 - length from the anterior-most point of the metaconid to the posterior- most point of the metastylid. mcch - crown height measured from the occlusal surface to the base of the crown along the metaconid. Itrl - lower toothrow length measured from the anterior-most part of the p2 to the posterior-most point of the m3. Idl - lower postcanine diastema length measured between the alveoli of the c· and p2 (excluding dpl if present). MATERIALS AND METHODS Gulf Coastal Plain terrestrial vertebrate faunas from both Texas and Florida range in age from the Arikareean to the Recent (Tedford and Hunter 1984); the taxa under study here are from the later half of the Miocene (about 14 to 6 ma). This study includes all material referable to Calf \Fh 11111111, lor,I,1111'-=Lv--9~, 10/.41 44, %* *f' '11% ~ZZ~-~A 0 4. 0 7 5. 69 Figure 20. Occlusal views of upper and lower cheekteeth of Calippus (Grammohippus) maccartyi n. sp. from the early Hemphillian of Florida. A-B, E. Moss Acres Racetrack Site, Marion County. C-D. Withlacoochee River UF Locality 4A, Marion-Citrus County line. A. UF 69951, L P2-M3; holotype, teeth restored to their natural relative positions. B. UF 90299, L M12. C. UF 45536, R M12. D. UF 53462, R p34. E. UF 69951, L p4-m2, holotype (same individual as teeth figured in 2OA). 278 BULLErIN FLORIDA STATE MUSEUM VOL. 32(3) of Nann»us and two of Connoh*pan-on) are also from the newly discovered Moss Acres Racetrack Site. UF 69951 consists of the anterior (pre-orbital) half of a skull, but it has been crushed laterally such that no facial characters can be recognized. The specimen does suggest that any fossae were shallow at best. The premaxillary region is the least damaged part of the cranium, but it is still cracked and distorted. The teeth that are present, however, are very well preserved, except for the left I3, which has the top 10 mm of its crown broken off. Much of the mandibular symphysis is preserved intact and undistorted. The incisors display the characteristic Calippus morphology (Fig. 21): i12 are aligned in a straight row; the i3 was originally positioned at a sharp angle to them, but with wear its occlusal surface has become aligned with that of the i12. The width across the i3s of UF 69951 is 58.4 mm. Due to the post-mortem crushing, this value is probably within 2 mm of the true width and is probably too small (as the teeth are compressed laterally). The diastema between the i3 and c is short (4.6 mm). The left c is 7.5 mm long and 6.1 mm wide. Upper cheekteeth of C. maccartyi (Table 10 ; Figs. 20A-20C) are smaller than average-sized individuals of C. cemsinus or C. hondurensis, but fall within their observed ranges. UF 69951 is an adult, with the occlusal surface of the M3 fully worn, and an Ml MSCH of about 27 mm. The P2 of UF 69951 seems relatively more heavily worn, perhaps pathologically, when compared to the other teeth. The P2 protocone is short and rounded, with a broad connection to the protoselene. It has no pli caballin, and the hypoconal groove is a small lake on the left side, while the right side has lost all trace of it. Fossette plications are limited to a vestigial pli prefossette and a single, modest pli postfossette. The metastyle is still relatively prominent. On the less worn UF 95407, there is a small pli caballin, a deep hypoconal groove that is in the process of being closed off by a labial pfojection from the hypocone, and an oval, very obliquely oriented protocone. The fossettes are also simple, although the single pli prefossette and pli postfossette are deeper than in UF 69951. On the P3 and P4, the protocone is large, more elongate- oval in shape, oriented anterolabial-posterolingually, and with a slightly flattened lingual border (Fig. 2OA). The preprotoconal groove is moderately deep, so that the protoconal connection is notably constricted. A single, small pli caballin is present on both the P3 and P4 of the type. The more heavily worn premolars from the referred Withlacoochee 4A sample lack pli caballins, but still have moderate preprotoconal grooves. The P4 of UF 69951 retains an open hypoconal groove, while the P3 has an isolated lake. The preprotoconal grooves of the Ml and M2 are shallower than those of the premolars, thus broadening the protoconal connection, and the protocone is less obliquely oriented (Fig. 20A). The type Ml and M2 both lack a pli caballin, but the less worn UF 90299 has a very small one. The hypoconal groove closes on molars variably during ontogeny; it would close on UF HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 279 90299 at an MSCH of about 20 mm, but would be present until late wear on UF 45535. On both M35 the hypoconal groove opens directly into the postfossette, a not uncommon condition in equid M3s. The M3 of UF 69951 also has an isolated protocone, a feature not observed in a sample of 25 specimens of C. cerasinus from the Love Site. An isolated protocone is rarely observed in M3s of C. martini. Molars in early wear-stages (as exemplified by UF 90299) have very deep preprotoconal grooves. The fossettes of the P3-M3 are similar. A pli hypostyle or pli protaloph are not observed, except during earliest wear-stages. The opposing inner fossette margins are closely appressed (Figs. 2OA-2OB), more so than in other species of Grammohippus. Fossette plications are shallow, unbranching and not numerous, but are retained until the MSCH reaches about 20 mm or less. 0 2cm 1 1 Figure 21. Occlusal view of mandibular symphysis of Calippus (Grammohippus) maccart¥i n. sp.; UF 69951, holotype; from Moss Acres Racetrack Site, Marion County, Florida. Teeth present: R il-B; L il-i3, c; R side of symphysis is broken and the i3 has been restored to near its original position. 280 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) With the limited sample, unworn crown heights are not directly observable. The specimen with the greatest MSCH (UF 45535, 40.2 mm) has formed roots and has a completely worn occlusal surface. Therefore, its unworn crown height would have been at least 5 to 10 mm greater. ROC of available specimens of C. maccartyi varies from 55 to 85 mm, much greater than that of C. cerasinus or C. hondurensis (their OR is 38-50 mm). The crowns are not as straight as those of C. (Cah*us), however. The lower cheekteeth of C. maccartyi (Table 10; Figs. 2OD-2OE) are considerably advanced over other species of Grammohippus, with large, widely flairing metaconids and metastylids. They greatly resemble the basic enamel pattern observed in Astroh*us, as the metaconid, metastylid, and unpenetrated isthmus form a "Y" (Fig. 2OD). In premolars (Figs. 2OD-2OE), the ectoflexid is shallow, the labial borders are rounded or only slightly flattened, and the lingual flexids are deep and persistent through much of the crown. The metaconid of the p2 is large and well developed. In earliest wear- stages, there may be plications extending posteriorly from the isthmus and/or protolophid on both premolars and molars. Molars resemble premolars more than in any other species of Cal*us, but do differ in their deeper ectoffexids and narrower occlusal surfaces. On p3 to m3, the protostylid is a variably developed ridge that extends to near the top of the unworn crown, and that often becomes more prominent with wear (Fig. 2OD). Even extremely worn molars (e.g. UF 53463) retain well developed lingual flexids. Discussion.- Calipplis maccanyi is recognized from only two early Hemphillian localities in north-centfal Florida. The combined presence of Indarctos and Machairodus at Withlacoochee 4A indicate a late early Hemphillian age (Becker 1985; Tedford et al. in press A). Neither is present at Moss Acres, but its fauna (Table 13) also indicates a younger age than either the Mixson's or McGehee local faunas. Those species that it does share with these two earlier Hemphillian faunas (e .g . Cormohipparion ingenuum and C. plicatile) are represented by morphologically more advanced individuals (Hulbert, in press B). Other taxa, e.g. Nannippus minor and Aphelops mutihis, are represented by more advanced species. Thus, the Moss Acres Racetrack Site is probably late early Hemphilliari, but perhaps not as young as Withlacoochee 4A. C maccartyi represents one of the youngest known species of C. (Gmmmoh*us) and is the most derived in terms of dental evolution. The lower cheekteeth of C. maccanyi resemble those of Astrohippus,· however, this is interpreted to represent parallelism and not an especially close phylogenetic relationship (see below). Pseudhippan'on simpsoni is a third equid lineage that evolved a similar morphology (Webb and Hulbert 1986). HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 281 GENUS Protohippus LEIDY, 1858 Type Species.- Protoh*pusperditus (Leidy), 1858. Included Species.- P. vetus Quinn, 1955 ; P. supremus Leidy, 1869 ; P. gidleyi n. sp. Chronologic and Geographic Distribution.- Late Barstovian through early Hemphillian of Great Plains and Florida; Barstovian and early Clarendonian of Texas Gulf Coastal Plain; possibly Clarendonian of California. Revised Diagnosis.- Medium- to large-sized, hypsodont, tridactyl equids with toothrow lengths generally between 125 and 145 mm in mature individuals. Malar fossa absent. DPOF large, teardrop-shaped, relatively shallow; distinctly rimmed dorsally and posteriorly in earlier populations, often with a small posterior pocket; less distinct in later populations, without a pocket. Lacrimal bone large, included in posterior region of DPOF. Diastema short; rostrum broad, but not to the degree of advanced species of Calippus,· incisors form typical equine rounded arcade. Upper cheekteeth with large, elongate-oval protocones that are isolated from the protoselene to varying degrees during early wear-stages (most prevalent on P34 and M3); moderately large, single pli caballins on P34 (smaller and less persistent with wear on molars); simple but relatively persistent fossette plications; hypoconal groove generally remains open until at least middle wear; prominent parastyles on P34. Large protostylids on permanent and deciduous lower cheekteeth. Variably developed ectostylids on dp2-dp4. Discussion.- Leidy ( 1858) first named Protohippus as a subgenus of Equus, but later (e.g. Leidy 1869) raised it to generic rank. It was commonly used in the latter half of the 19th Century; Leidy, Marsh, and Cope described a total of 11 species of Protohippus before 1900 (Gidley 1907). However, many of these were subsequently regarded as synonymous and/or belonging to other genera (Stirton 1940; Webb 1969), and only four species of Protohippus are here recognized as valid. In a series of papers based on an increasing number of relatively complete specimens with more accurate locality data, Gidley (1904; 1906; 1907) was able to redefine Protoh*us and clearly distinguish it from Pliohippus and Merychippus. Gidley's ( 1907) concepts of Pliohippus and Protohippus were essentially followed by Osborn (1918) and Matthew (1926). McGrew and Stirton (e.g. McGrew 1938; McGrew and Meade 1938; Stirton 1940) proposed a horizontal reorganization of these taxa, in which a number of "primitive" species thought ancestral to a number of advanced genera were all placed in a single genus, Megch»us. P. perditus (the genotype) was one of these, thus Protohippus was synonymized with Megchippus, although retained as a subgenus. The chronologic age of a species played a major role in determining its generic 282 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) assignment in this scheme. They considered the boundary between the Miocene and Pliocene to fall between the Devil's Gulch and Burge Faunas, and all late Miocene non- anchitherine equids were placed in Metychippus sensu lato. The characters they used to define Me,ych*us are all primitive, and can no longer be considered valid reasons for taxonomic grouping. MacFadden and Skinner (e.g. MacFadden and Skinner 1981; MacFadden 1984a) have recognized pre-Burge equid populations with Me,ychippus-grade dentitions as members of advanced genera (H*parion and Connoh*parion). A similar, vertical repartitioning of the taxa Stirton (1940) assigned to Metych*pus (Protohippus) is therefore appropriate, and can be based on the stratigraphically controlled Frick collection of crania and associated dentitions. The phylogenetic relationships of Protoh*pus with other genera will be discussed at length below. Quinn (1955:54) proposed the new genus Eoequus for a single specimen from the late Barstovian of the Texas Gulf Coastal Plain. As the name suggests, Quinn (1955:58) considered the new taxon to be directly ancestral to Equus. The holotype of Eoequus wilsoni is a young adult that is referred below to Protoh»us perditus. Eoequus thus becomes a junior syn6nym of Protohippus. Protohippusperditus (LEIDY), 1858 Fig. 22A; Tables 14-16 Equus (Protoh*us) perditus LEIDY 1858:26-27. Protohippusperdints (Leidy), LEIDY 1869:275-277; GIDLEY 1906:136-139 (in part); GIDLEY 1907:882-883 (in part); OSBORN 1918:129-130; QUINN 1955:19-21 (in part); EVANDER 1978:41. Protohippus or Hippotherium profectus COPE 1889:441. Me,ychippus perditus (Leidy), COPE 1892:943 ; MCGREW and MEADE 1938:200-202; STIRTON 1940:182; HESSE 1943:168-169; FORSTEN 1975:31. Eoequus wilsoni QUINN 1955:54-58. Merychippus circulus (Quinn), FORSTEN 1975 :32-35 (in part). Type Specimen.- USNM 619, a R maxillary fragment with P4-M3 (Leidy 1869, plate 17.1, 17.2). Type Locality and Horizon.- From "the valley of the Niobrara River" (Leidy 1858:20) in Nebraska. Probably from the Valentine Formation (Devil's Gulch or Crookston Bridge Member?) or stratigraphic equivalent, late Barstovian. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 283 Distribution.- Late, but not latest, Barstovian (about 12 to 14 ma) of the northern Great Plains and the Gulf Coastal Plain of Florida and Texas. Referred Specimens.- Devil's Gulch Fauna, Devil's Gulch Horse Quarry, Brown Co., NE: F:AM 60350-60352, 60358, and 114067 5 skulls; F:AM 114091 mandible with dp2-m2. There are many additional, mostly uncatalogued, crania, mandibles, and teeth in the F:AM collection from this fauna. Material from the slightly older Crookston Bridge (Evander 1978) and Norden (Skinner and Johnson 1984) Faunas is also referable to P. perditus, and is principally housed in the UNSM and F:AM collections. Cold Spring Fauna. Cold Spring Local Fauna, San Jacinto Co., TX: TMM 31219-165 assoc. R DP2-DP4,Ml-M2 and L DP2-DP4,M2-M3; -230 partial skull with R DP3-DP4,Ml-M2 and L DPl-DP4,Ml-M2; -61, -328 2 L P2; -253 R P34; -329, -330 2 L P34; -331, TAMU 3030 2 R M12; TMM 31219-332 L M12; -333 R M3; -5 L M3; -203 assoc. R and L mandibles with dp2-dp4 (probably same individual as 31219-165); -43 R mandible with dp2- ml (probably same individual as 31219-230); -204 R mandible with p4-m3; - 337 L mandible with p2-ml; -138 L assoc. p4-m3; -168 assoc. (?) L p3-p4; TAMU 3027 R dp4; TMM 31219-334 R p2; -336 R p34; -335, TAMU 3028, 3029 3 L p34; TMM 31219-338-340 3 L m12. Noble Farm Local Fauna, Grimes Co., TX: TAMU 3031-3033 3 R P34; 3034 L M12; 3035 L mandible with dp2-m2; 3036 R p34. Chapel Hill, Washington Co., TX: TMM 31272-8 L M3. Goodrich Local Fauna, Polk Co., TX: TMM 31183-30, -37 and -66 assoc. skull with R and L P2-M3 and R and L mandibles with p2-m3 (holotype, Eoequus wilsoni; Quinn 1955, plates 10-13). Bradley Fauna. Kingsford Mine (Paige No. 1 Dragline), Polk Co., FL: UF 61344 L Ml. Revised Diagnosis. - Slightly smaller and less hypsodont than P. supremus, with toothrow lengths of about 120 to 135 mm and unworn molar crown heights of about 47 mm. Relatively short postcanine diastema and large DPl. Shorter, more oval protocones than P. supremus or P. gidleyi; also shorter metaconid-metastylid complexes and entoflexid lengths. Description.- The holotype of Protoh*us perditus (Osborn 1918, Fig. 102) lacks precise locality data, and was recovered from a region where vertebrate fossils have been found ranging in age from the early Miocene to the Pleistocene. A large sample of upper dentitions from the Devil's Gulch Horse Quarry (DGHQ) closely match USNM 619 in size and morphology, and are here referred to P. perditus following unpublished work by Morris Skinner. This sample also includes associated mandibles and crania, thus permitting a more complete description of one of the earliest named North American equid species. The cranial morphology of P. perditus is well preserved on several skulls from the DGHQ, especially F:AM 60350 and 60351. No malar fossa or depression is evident on these specimens, as well as USNM 619 or 'IMM A B thim C D '1 lillill, , >L -/ 1 4«64 E F 1/\ , 0/ ,/'-5\ 0 2cm 1 Figure 22. Occlusal views of upper cheekteeth of Protohippus from Florida. A. UF 61344, P. Derditus, L P4, Kingsford Mine, Bradley Fauna (late Barstovian), Polk County. B. UF 28553, E. supremus, L P4, Grey Zone, Phosphoria Mine, Agricola Fauna (early Clarendonian), Polk Count9. C-F. P. Ridlevi n. sp., Love Site, latest Clarendonian, AIachua County. C. UF 62482, L P2. D. UF 62497, R P34. E. UF 62500, R P34. R UF 62540, R M12. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 285 31183-30 (Quinn 1955, Plate 12). The DPOF is large, oval or teardrop- shaped, and runs from above the anterior half of the M3 to the posterior half of the P3. Its greatest length is about 80 mm; its maximum height measured perpendicular to the latter and just posterior to the IOF is about 45 mm. The posterior and dorsal margins of the DPOF on the lacrimal and nasal bones are well rimmed, and there is a slight posterior pocket. The preorbital bar is relatively narrow (about 13.5 to 15.5 mm). The postcanine diastema is shorter than that of P. supremus, and the incisor region is only slightly expanded (Fig. 3; the muzzle width is about 38% of the UTRL). A relatively large DPl (12 to 13 mm long) is retained with the adult dentition, functionally occludes with the p2, contains several distinct cones and lophs, and resembles those ofPliohippus. The upper cheekteeth of P. perditus (Table 14; Fig. 22A) are characterized by oval (elongate-oval in early wear) protocones that are isolated from the protoselene in very early wear-stages (Quinn 1955, Plate 10.1), but which then rapidly connect. When isolated, the protocones have large anterolabial spurs. Protocones of the premolars are notably shorter than those of the molars. In heavily worn molars, the protocone not uncommonly connects with the hypocone. Fossette plications are relatively simple and not as numerous as in P. supremus or P. gidleyi·, nor is the prefossette loop so well formed. By moderate wear-stages, only a single pli prefossette and pli postfossette remain (Fig. 22A). The hypoconal groove remains open until moderate wear; it may simply fade with wear or persist as an isolated lake. The pli caballin is generally less prominent than in P. supremus or P. gidleyi and is frequently absent in moderately worn teeth. The upper cheekteeth are moderately curved, with ROC usually about 45 to 55 mm. Examples of measurable slightly worn or unworn teeth are rare. MSCHs for the slightly worn P2 and P) of TMM 31183-30 are about 36 and 42 mm, respectively. The slightly worn Ml of TMM 31219-230 has an MSCH of 43.3 mm. Two very slightly worn molars from the DGHQ have MSCHs of 42 and 45 mm. Thus unworn MSCH of the M12 probably lies between 45 and 50 mm. The DP2-DP4 resemble the permanent cheekteeth, but the protocone is relatively much shorter, and the fossette plications are more numerous and persistent in early wear-stages (e.g. TMM 31219-165). Small pli caballins are present and the hypoconal groove remains open even in heavily worn DPs. Lower cheekteeth (Table 15) are typically protohippine, with large protostylids on p3-m3 and dp34. The metastylid is equal or subequal to the metaconid in size. Permanent premolars in early wear most often have a long isthmus that connects to the metaconid, and the metastylid buds off the metaconid posteriorly and lingually. In some, the ectoflexid can be deep and penetrate the isthmus to varying depths (this morph is very common in the Cold Spring sample). In the majority of observed premolars from the 286 BULLEnN FLORIDA SrATE MUSEUM VOL. 32(3) DGHQ, the ectoflexid is shallow and does not, or only shallowly, penetrate the isthmus, however. The metaftexid contracts rapidly with wear (the primitive protohippine condition), as do the linguaflexid and entoftexid to a lesser degree. The p2 and dp2 have flattened anterior margins. Molars greatly resemble those of Calippus mallini, except for the strong protostylids, slightly larger metastylids, and lesser mcch. The moderately well-cemented deciduous lower premolars are characterized by deep linguaftexids and ectoflexids that nearly divide the tooth. With wear, the linguaflexid retreats, along with the metafiexid, leaving a broad area of confluence between the metastylid, metaconid, and protoconid. Moderate wear exposes large ectostylids on the dp2-dp4, that rise about 5 to 6 mm above the base of the crown. Heavier wear reveals hypostylids that are especially well developed on the dp3. Discussion.- Protohippus perditus has long been recognized as a characteristic member of the fauna from lower units of the Valentine Formation (McGrew and Meade 1938). However, Gidley's (1907) "neotype" of P. perditus (AMNH 10838) from the Clarendonian of South Dakota is instead referable to Calippus martini (Hulbert 1987a). The relatively complete referred material from the Valentine Formation allows a better understanding of P. perditus and aids the generic diagnosis. The referred specimens from the Gulf Coastal Plain, including the type of "Eoequus" wilsoni and UF 61344, resemble that from the DGHQ and USNM 619 in size, hypsodonty, and general dental morphology (Table t 16; Fig. 22A), and indicate that the species was wide-spread during the late Barstovian. Protoh*us profectus was recovered along with the type of Pseudhipparion retrusum (Cope 1889), which suggests a late Barstovian age. It is synonymized with P. perditus rather than P. supremus because of its smaller size, weak fossette plications, and less well developed pli caballins. In the lower units of the Valentine Formation, P. perditus is found in lithosympatry with the slightly larger Pliohippus mirabilis (Leidy 1858). P. mirabilis differs from P. perditus in its very deep DPOF, its well developed malar fossa, and a number of dental characters outlined in Table 17. The two cannot be synonymous, as was proposed by StirtOn (1940:182). Protoh*us supremus LEIDY, 1869 Figs. 22B, 23; Tables 14-16 Protohippus supremus LEIDY 1869:328 (in part). Protoh*pus simus GIDLEY 1906:139-140; GIDLEY 1907:925-926; OSBORN 1918:136-138. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 287 Pliohippus supremus (Leidy), GIDLEY 1907:889-890 (in part); OSBORN 1918:150-151; STIRTON 1940:192; QUINN 1955:24-26 (in part); WEBB 1969:83-95 (in part); FORSTEN 1975:53. Pliohippus simus (Gidley), MCGREW and MEADE 1938 : 201 ; STIRTON 1940:192. Hippotigris sellardsi QUINN 1955 :46-48. Hippotigris clarendonensis QUINN 1955,49-50. H*potigtisparastylus QUINN 1955:50-51. Pliohippus martini (Hesse), FORSTEN 1975 :48-53 (in part). Pliohippus (Pliohippus) cf. P. supremus (Leidy), FORSTEN 1975 : 53-61 (in part). Lectotype Specimen.- ANSP 11280.1, a slightly worn L P34. Selected by Gidley (1907) from the syntypic series, he referred to it as a Ml, but his measurements clearly indicate which specimen he chose as the lectotype, as Later figured by Osborn (1918, Fig. 118.2). Type Locality and Horizon.- Exact locality unknown, Little White River region, South Dakota. Probably Clarendonian deposits of the Ogallala Group. Distribution. - Latest Barstovian and Clarendonian of northern Great Plains (about 10.0 to 12.0 ma); Clarendonian of southern Great Plains, Gulf Coastal Plain of Florida and Texas. Referred Specimens.- Little White River region, SD: AMNH 980 partial skull with R I3, R and L DPl-M3 (type, P. simus); AMNH 10871 L maxilla with P2-P4, M2-M3. Burge Fauna. Burge Quarry, Cherry Co., NE: F:AM 60353 assoc. skull, rami, and postcranial skeleton; 60356 skull with R and L DPl-M3; 108187, 114058-114063 7 maxillae or palates; 60357 assoc. skull, R and L rami; Midway Quarry, Cherry Co., NE: F:AM 60354 assoc. skull, R and L rami. Clarendon Fauna. MacAdams Quarry, Donley Co., TX: F:AM 111728 assoc. skull and rami. C. Risley Ranch Site, Donley Co., TX: TMM 255-29 R mandible with p3-m3 (type, H. clarendonensis); TMM 255-17 L m12. Lapara Creek Fauna. Bridge Estate Site, Bee Co., TX: TMM 31132- 284D R P34; -541, -542 2 R M12; -459 L mandible with p2-m3 (type, H. pamstylus), -335 assoc. p4,m2-m3; -237 L m12. Buckner Ranch Site, Bee Co., TX: TMM 30896-503 assoc. R and L P2-M3 (type, H. sellardsi); -206 and - 541 assoc. mandibles with R p3-m3 and L p2-m3; -240, -476 2 R mandibles with dp2-ml; -420C, F assoc. L m2-m3; -447 R p34; -420(} L p34. Farish Ranch Site, Bee Co., TX: TMM 31081-1183 L p34; -664 R mandible with p2- m3; -168E, F assoc. p4-ml; -1210 L p2. Late Agricola Fauna. Gray Zone, Phosphoria Mine, Polk Co., FL: UF 28553 L P34. Nichols Mine, Polk Co., FL: UF 25125 R P4. 288 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) Revised Diagnosis.- Large Protohippus with toothrow lengths of a66ut 130 to 145 mm and unworn molar crown heights of about 54 mm. Larger and more hypsodont than P. perditus, with a broader muzzle, smaller (on average) DPl, more elongate protocone, and more complex fossette plications. Hypoconal groove present until late wear-stages; forms lake on premolars. Protocones isolated from protoselene in early wear-stages of P3-M2, until moderate wear on M3; not as isolated as those of P. gidleyi. Metastylid large , well separated from metaconid by well developed, persistent lingual flexids especially on premolars. Description.- Based on AMNH 9820 (holotype, Protoh»us simus) and a number of crania from the Burge Member of the Valentine Formation, the facial region of P. supremus greatly resembles that of the genotypic species, P. perdims. No malar fossa is present. The DPOF is approximately the same size and in the same position as in P. perditus, but it is notably shallower and less well-rimmed (Osborn 1918, Plate 21.1). The Burge specimens retain a well defined posterior rim and a very slight pocket. Clarendonian specimens (e.g. AMNH 9820 and F:AM 111728) have an even shallower and less well defined DPOF without a posterior pocket, but are otherwise identical to the latest Barstovian (Burge) population. As noted by Gidley (1906) in his description of P. simus, the muzzle is very broad (about 45% of the UTRL), much greater than that of a similarly sized, typical equid (Fig. 3). The first two incisors are not linearly arranged , as in Calippus, but· are slightly arcuate . The upper cheekteeth of P. supremus (Tables 14, 16; Figs. 22B, 23) have very strong styles, including a well developed metastyle. The P2 has a shorter, rounder protocone than the other teeth; it is connected to the protoselene in all known specimens. The fossettes of the P2 tend to be simpler, and the hypoconal grooves close earlier than in the P34. The P34 have large, widely open parastyles and mesostyles, and small metastyles that are retained until late wear-stages. The protocone of the P34 is elongate; with wear it becomes shorter and wider. In early wear-stages, the protocone is isolated from the protoselene, but has a large labially directed spur. With wear, the spur connects with the protoselene (Fig. 23); this connection is at first greatly constricted by a deep preprotoconal groove, this condition persists until at least moderate wear-stages. The P34 protocone orientation is markedly oblique (Fig. 22B), and, in late wear-stages, the protocone does not connect with the hypocone. The P34 have a large, usually single (but occasionally branched) pli caballin that is reduced and lost at MSCHs of about 25 to 30 mm. The hypoconal groove remains open at least until moderate wear-stages; it closes to form a lake and disappears at a greater crown height than in the molars. Fossette plications are relatively complex and persistent for a protohippine, as only very greatly worn P34 totally lack plications (Fig. 23). A pli protoloph and pli hypostyle are uncommon, but occasionally found on slightly worn teeth. The posterior half of the prefossette almost always has 2==-=YAL IE»r- 2-LI71 ',0416-&5*A IS-~an}s-se, 11 le).410410 .-:: vi. * Be,i~--*-5' kEY.74:/ Ct---61'78400/*FF- -,/~5$%1 ~Ii»Z-V i..P' . H U LB E R T: G U LF C O A S TA L P LA IN P R O TO H IP P IN E S 289 14-6- .2.. W , r X\/2/4#A'...7 -'. I ...-, ....V- * 711//7 C WAI.-vv~~a 'fl 1,4/7,9 .k ~G356%~Sh -*. \, / B/ I *-. liliC: - C ,9 - b' I 'r . 4 9 1 #1 %?mre' 11 1 2;f / t. Figure 24. Occlusal views of upper and lower cheekteeth of Protohippus gidlevi n. sp. from the Love Site, latest Clarendonian, Alachua County, Florida. A. UF 6247j, associated R P2-M3, holotype, early moderate wear-stage. B. UF 32298, associated L.P2-M3, late moderate wear-stage. C. UF 32173, associated R p2-m3, paratype, moderate wear-stage. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 297 smaller prefossette loops. The protocone of the M3 is connected to the protoselene by a very narrow isthmus; most M3s of similar MSCH in the topotypic sample have isolated protocones. Upper cheekteeth of P. gidleyi (Figs. 22022E, 24A-248; Tables 14, 16) resemble those of P. supremus in most regards. They are only moderately curved, with ROC of molars between 50 and 60 mm. The P2 in early wear A f B. %3 uft)/ \ /11111/44.- 1- f '"Iff!#ift~ ~' f 4411111111111,~ ~ 4' 1 [ ID , IPAI '' linr74"iMP94\\< , '. ~ ~~~1/j' . A m d -, j, B C D ll#in A C'f) 1.3= C Jj L / Vl/l _/ - 1 g I'-VittjL, ,\/' 4(-7 0 2cm 42+ 4 Figure 25. Occlusal views of upper and lower cheekteeth of Protohippus gidlevi n. sp. from the Love Site, latest Clarendonian, AIachua County, Florida. A. UF 67704, associated R p3- p4, early wear-stage. B. UF 67769, L m12, early wear-stage. C. UF 45622, R m12, early moderate wear-stage. D. UF 90274, L dp34. E. UF 65232, R DP34. 298 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) (Fig. 22C) has a rounded, isolated protocone with a spur, and the postprotoconal valley is often confluent with the prefossette (e.g. UF 62481, 62482). A strong metastyle is usually present, but it tends to fade with wear, as does the pseudoparastyle. The anterostyle is often weak, giving the P2 a more blunt appearance, rather than its usual triangular form. The prefossette and postfossette are confluent in over half the sample of P23 from the Love Site, although they are separate in almost all of the heavily worn specimens (Fig. 24B). In early wear, the P2 can have well plicated fossettes (e.g. UF 62476), but these soon fade with wear, leaving at most a single pli prefossette and pli postfossette. Pli caballins are rarely present, and almost always weaker than those of the P34. With wear, the protoconal connection widens, the fossettes lose all plications and become more narrow, and with heavy wear the hypoconal groove is lost. The P34 (Figs. 22D-22E) have strong styles, including metastyles, deep hypoconal grooves that persist until about 45% of the crown is worn (Fig. 26), and moderately complex fossettes. The hypoconal grooves are almost always lost without forming a lake. A single, generally small pli protoloph or pli hypostyle is occasionally present in the upper quarter of the crown. In early wear-stages, the posterior half of the prefossette may have up to four (two or three are more common) plications, and the anterior half of the postfossette usually bears one or two. The prefossette loop is well developed, but is usually not as long as in P. supremus. Moderate to heavily worn P34s generally retain one or two plis prefossette and a single, deep pli postfossette. These too tend to be lost as MSCHs reach 21 mm and less. This is also the period when the pli caballin is usually lost. The protocones tend to be long, often with flattened to slightly concave lingual borders. The MSCH at which the protocone attaches to the protoselene is variable (Fig. 26), but usually between 30 and 40 mm. Prior to connecting, the protocone bears a large, anterolabial spur (Fig. 22E). After the connection, the preprotoconal groove remains deep until latest wear- stages (Fig. 24B). The M12 tend to be of about the same APL as the P34, but somewhat narrower (Table 14). As is typical for protohippines, the fossette plications are less numerous and are lost at earlier wear-stages than the P34, and pli caballins are found in only the earliest wear-stages (Figs. 22F, 24A). The protocone is connected rapidly with wear, is oriented much less obliquely than in the P34, and becomes connected to the hypocone with heavy wear. The protoconal connection remains constricted throughout much of the crown, with a deep preprotoconal groove. Metastyles are much less prominent than on the P34. The hypoconal groove remains open until the MSCH reaches 20 mm or less. Unworn or slightly worn MSCHs are about 39 mm for P2, 50 mm for P34, and 58 mm for the M12. Deciduous upper premolars are narrower counterparts to their permanent successors (Fig. 25E). The DP2 has a short protocone and a poor HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 299 pli caballin. The DP34 have elongate protocones, generally strong pli caballins, well developed Styles, and moderately simple fossettes. The hypoconal groove is deep and a pli dihypostyle is usually present. Lower cheekteeth of P. gidleyi (Tables 15-16; Figs. 24C, 25A-25D) especially resemble those of P. supremus, the principal difference being that the younger species tends to exhibit advanced features, such as elongated metaconids and metastylids, through a greater percentage of the crown. The paratype, UF 32173, is a typical example of a moderately worn individual (Fig. 24C). Deep lingual flexids are retained on all but the ml, which is starting to lose the metaflexid and shorten the metastylid. The lower premolars retain expanded metaconids and metastylids and relatively deep lingual flexids even at crown heights of less than 20 mm. In very early wear-stages, the bases of the metaflexid and entoflexid may bear several plications (Fig. 258), but these are soon lost with wear. The p34 ectofle]rid is a broad "V," generally penetrating into the isthmus to a depth about that of the base of the entoflexid (Fig. 25A). The ectofiexid of the p2 is shallower, not penetrating the isthmus, and the paraconid is usually angular in moderate to early wear- stages, becoming more blunt with heavy wear as in P. supremus. In the molars, the ectoflexid almost always separates the isthmus. In early wear- stages, the deep, "V"-shaped linguaflexid and the ectoffexid nearly completely separate the metaconid and metastylid, except for a narrow commissure (Fig. 250. With wear, both retreat, so that there is greater dentine confluence between the metaconid and metastylid (Fig. 240. In early to moderate wear- stages the metastylid is nearly as large as the metaconid, but tends to be angular while the latter is more rounded. Only in later wear-stages is the metastylid noticeably smaller and less lingually placed than the metaconid. Moderate protostylids appear on the occlusal surface shortly after the onset of wear on the p3-m3, and may at first be isolated from the protoconid (e.g. the m2 of UF 67704); they are stronger in p34 than ml-m3, but vary with age. The labial borders of the protoconid and hypoconid are rounded. Lower deciduous premolars are like those of P. supremus (Fig. 250), but have more rudimentary ectostylids. The strong protostylids, however, serve to distinguish them from the dp2-dp4 of Plioh*us. As in the permanent teeth, the protostylid is often isolated from the protoconid in early wear-stages (e.g. UF 64402). Cranial features of P. gidleyi are known only from UNSM 9064, a nearly complete skull from the referred Nebraskan population. The dentition of UNSM 9064 is extremely worn and nondiagnostic (except to indicate that it is a protohippine or equine). The broadened muzzle and short diastema distinguish it from Dinohippus, the only other large equine in the fauna. It is larger and with a less broadened and robust muzzle than in advanced species of C. (Grammoh»us). The facial region of UNSM 9064 has been distorted by crushing, and the depressions in the malar region are of post-depositional 300 BULLETIN FLORIDA STATE MUSEUM VOL. 32(3) A22578569 - 90 - ....... - 70 - 50 euooojold pejoeuuoo % eA ooiB leuooodA 4 u e d o % - 30 -10 10 15 20 25 30 35 40 45 50 crown height (mm) 822578669 - 90 - - 70 - ~5Z;5555 -50 -30 - 10 10 15 20 25 30 35 40 45 50 crown height (mm) Figure 26. Histograms indicating at what wear-stage the protocone connects to the protoselene, and the hypoconal groove becomes closed in upper third and fourth premolars of the Love Site population of Protohippus gidlevi n. sp. A Percentage of specimens in each 5 mm wear-class with (shaded) and without (unshaded) connected protocones. All specimens with less than 50% of original crownheight have connected protocones. B. Percentage of specimens with open hypoconal grooves (unshaded) and those that have lost the hypoconal groove (shaded). Numbers above each wear-class indicate the sample size for each group. HULBERT: GULF COASTAL PLAIN PROTOHIPPINES 301 origin. The dorsal facial region of the somewhat better preserved right side indicates the presence of a faint DPOF located very anterior to the orbit, dorsal to the M2 to P3, and about 50 mm long. It is not distinctly rimmed or pocketed. Small alveoli indicate that a DPl was retained with the permanent dentition. Discussion.- Protohippus gidleyi is the youngest and most derived species of Protoh*pus. Unworn crown heights of its cheekteeth are about 5% greater than those of P. supremus. Its lower cheekteeth have the most expanded metaconids and metastylids of any protohippine, and elongated metaftexids and entoflexids remain deep until very late wear-stages. The most interesting trend evident in P. gidleyi is the tendency for increased isolation of the protocone from the protoselene. Possession of isolated protocones is generally considered structurally inferior to the connected condition (Stirton 1941). The trend in Protoh*pus for increased protocone isolation, along with the successful radiation of the hipparionines, suggests that this hypothesis is incorrect. The topotypic sample of P. gidleyi contains a number of upper and lower dentitions, along with many isolated cheekteeth, thus allowing a good estimate of individual and ontogenetic dental variation. Several early Hemphillian sites from Florida contain a few teeth that cannot be distinguished from the Love Site sample of P. gidleyi. UF 45521, a juvenile individual from the late early Hemphillian, is only provisionally referred to P. gidleyi. The protocone of the Ml is relatively small , and the fossettes are somewhat more plicated than in the topotypic population. A well represented sample from the late early Hemphillian of Nebraska suggests that the latter feature may be a chronoclinal trend within P. gidleyi. This sample is important, as it includes the only known skull of P. gidleyi. It demonstrates notable differences in muzzle and fossae morphology from Dinohippus, Pliohippus, and Cal*us and corroborates the dental evidence that the species belongs in Protohippus. The minor differences between the Love Site and Ft-40 populations are best explained by geographical variation and chronoclinal evolution. For example, the protocone of the M12 tends to be more isolated in the younger sample, surely a continuation of the trend observed throughout the entire genus. PHYLOGENY OF CALIPPUS AND PROTOHIPPUS, AND THEIR RELATIONSHIPS WITH OTHER EQUID GENERA Protohippus and Calippus are here hypothesized to form a monophyletic dade based on several shared derived cranial and dental character states. As with all attempts to examine the interrelationships of hypsodont equid 302 BULLETIN FLORIDA SrATE MUSEUM VOL. 32(3) genera, this analysis is hampered by a vast number of poorly known, late Hemingfordian and Barstovian species that lie at the base of the Miocene radiation of the Equinae. These species are all traditionally referred to the genus Megchippus. Problems associated with many of these primitive species are lack of adequate cranial material, poor sample sizes of cheekteeth, paucity of associated upper and lower dentitions, and inadequate stratigraphic data for type specimens. The following, therefore, is a preliminary assessment of phylogenetic relationships among protohippine and equine genera. Using the character states presented in Table 18, hypotheses of evolutionary relatedness of protohippines with other equid taxa were formulated using standard cladistic methods. Character state polarity was primarily determined by the outgroup method, i.e. the character state found in one or more taxa considered the probable sister group(s) of the taxa being studied is assumed to be primitive. Four outgroups were used: 'Tarah*us" leonensis; "Megch