Lucas et al., eds., 2008, . New Mexico Museum of Natural History and Science Bulletin 44. 273 SYSTEMATICS OF THE DROMOMERYCINES AND ALETOMERYCINES (ARTIODACTYLA: ) FROM THE AND OF

DONALD R. PROTHERO AND MATTHEW R. LITER

Department of Geology, Occidental College, Los Angeles, CA 90041

Abstract—The subfamilies Dromomerycinae and Aletomerycinae were part of an endemic radiation of North American Miocene and Pliocene cervoid artiodactyls characterized by a variety of bony horns. Their -level systematics has not been reviewed since Frick (1937), and the groups were oversplit with many redundant subgenera and 49 named species, most of which were nomina nuda (no diagnosis provided) and have not been analyzed since 1937. We use modern biological species concepts and statistical methods to greatly reduce the number of valid taxa in the subfamily. Among the Aletomerycinae, the late Arikareean immigrant contains three species, A. gracilis (with three junior synonyms), A. marslandensis, and A. occidentalis. The peculiar, curve-horned Sinclairomeryx is monotypic; two other species are junior synonyms of S. riparius. Among the Dromomerycinae, Drepanomeryx (Matthomeryx) matthewi is a junior synonym of D. falciformis. The bow- horned Rakomeryx sinclairi is also monotypic, with five junior synonyms. Straight-horned borealis is also monotypic (with three synonyms), as is Subdromomeryx antilopinus (raised to generic rank), which has four junior synonyms. As part of the simultaneous immigration event of the Cranioceratini in the late Arikareean, there is only one valid species, Barbouromeryx trigonocorneus, with two additional invalid subgenera and three invalid species. The common genus Bouromeryx, which had been split into eight species, contains only two: the smaller late Hemingforidan B. submilleri, and the Barstovian B. americanus. The monotypic three-horned Procranioceras skinneri remains valid, but is elevated to generic rank. , which has two straight supraorbital horns and its posteriorly-oriented occipital horn, once contained seven species, but now consists of the larger C. unicornis and the smaller C. teres. The cranioceratins Yumaceras (elevated to generic rank) still has three valid species, and Pediomeryx hemphillensis (with two synonyms) of the late Hemphillian is the last member of the lineage. Thus, 49 previously recognized species has been reduced to just 18 species in 12 genera (most of which are now monotypic) with no subgenera. This clarification of the taxonomic confusion of such an important group greatly enhances their usefulness in biostratigraphy and paleoecology.

INTRODUCTION and Manning, 1998). According to Janis and Manning (1998), both of these changes were due to the increased aridity and more open habitat, The dromomerycines and aletomerycines were -like groups and the decline of their preferred subtropical/temperate brushy/wood- of ruminant artiodactyls found in North America during the Miocene and land habitat. The last known dromomerycine, Pediomeryx hemphillensis, earliest Pliocene (Fig. 1). Most had brachyodont to mesodont dentitions is found alongside the first true cervid to immigrate to North America in and (based on the antorbital fenestrae in the skull) apparently had deer- the latest Hemphillian (earliest Pliocene, fide Tedford et al., 2004). Pre- like antorbital glands for scent marking. Dromomerycines and sumably the cervids took over this woodland browser habitat from the aletomerycines were distinguished by a great variety of bony horns with declining dromomerycines, or possibly cervids outcompeted the expanded terminal bulbs and no evidence for deciduous tips (unlike the dromomerycines (Voorhies, 1990; Webb, 1998), although Janis and Man- partially deciduous horns in antilocaprids, or the completely deciduous ning (1998) and Janis (2000) relate their to climatic events, not antlers in cervids). Unfortunately, Frick (1937) illustrated these append- to competition from immigrant cervids. As Janis and Manning (1988, p. ages with deciduous tips like those of pronghorns, and this practice was 488-489) noted, dromomerycines follow the trend seen in many other followed by later illustrators (e.g., Scheele, 1955). (In this paper, we will groups in that the late Hemphillian taxa were smaller than early and follow the common usage of “horn” instead of the more cumbersome but middle Hemphillian forms. neutral “cranial appendage,” recognizing that palaeomerycine “horns” Cope described the first known dromomerycines, “Cosoryx” teres were probably not covered by a keratin sheath as in the true horns of (Cope, 1874) from the Chamita Formation of New Mexico, bovids). Nearly all skulls of presumed males have unbranched paired and “” borealis (Cope, 1878), based on a partial skull from supraorbital horns, and the presumed males of the tribe Cranioceratini the Barstovian Deep River beds of Montana. At that time, Cope used the have a occipital horns as well. According to Janis and Manning (1998) genus Blastomeryx as a wastebasket for a variety of , including and Semprebon et al. (2004), dromomerycines and aletomerycines were several antilocaprids and dromomerycines, as well as blastomerycines. mostly browsers living in subtropical to temperate habitats from moder- Scott (1895) first noted that “Blastomeryx” borealis resembled the Euro- ately open bushland/grassland ecotone to dense woodlands and thickets. pean genus . Douglass (1899, 1903) described additional They are apparently related to the European genus Palaeomeryx (family material, and both Douglass (1903) and Matthew (1904, 1909) referred Palaeomerycidae), but dromomerycines and aletomerycines developed this material to Palaeomeryx borealis. In 1909, Earl Douglass recovered at least two endemic evolutionary radiations in North America after their nearly complete skeletal material of “Blastomeryx” borealis from the first arrival in the late Arikareean around 19 Ma. They quickly diversi- Deep River beds, and renamed it Dromomeryx borealis. In the ensuing fied in the Hemingfordian, and (like many other mammalian groups, such years, several more taxa were discovered, but were not considered related as pronghorns and horses) reached peak diversity in the early Barstovian, to “Blastomeryx” borealis. Sinclair (1915) described Drepanomeryx as after which they underwent both diversity decline and an increase in an antelope; Matthew (1918) described Cranioceras and also thought it body size during the Clarendonian and Hemphillian (Webb, 1983; Janis was an antelope. Lull (1920) described Aletomeryx, but thought that it 274 subfamilies have no equivalent in the work of anyone else, but are, on the average, of about generic rank. For instance, he places 15 genera of Ameri- can Cervidae in 13 subfamilies, and he apparently bases one or more subfamilies on subgenera, without any included genus.” A much more serious problem is the fact that most of his new taxa were inadequately diagnosed, so it is not possible for later workers to tell how Frick (1937) distinguished them. The requirement that all valid species have a diagno- sis was introduced to zoology during the International Zoological Con- gress in Monaco in 1913, and came into effect on January 1, 1931, after the International Zoological Congress in Padua in 1930. According to Article 13.1.1 of the current International Code of Zoological Nomencla- ture (1999), all names published after 1930 require a diagnosis. If they do not have one, they are nomina nuda. It is unclear why Frick did not follow the requirements of the codes of zoological nomenclature, but they were in force by 1930, and therefore binding on Frick’s (1937) . Nearly all of Frick’s (1937) taxa are nomina nuda by this criterion. The current Code recommends that these names should not be used, but later authors (e.g., Janis and Manning, 1998) have validated many of the generic (but not trivial) names despite their inadequate diagnoses. In most cases, it is impossible to see how anyone can distinguish most of the named species, since Frick performed no statistical compari- sons. He typically measured a only few specimens and then grouped them into rough size classes labeled by Roman numerals, but never used the statistical techniques that were coming into biology at the time, nor did he ever plot data from the specimens in a useful fashion. It is clear from a close examination of Frick’s specimens and his published work that his thinking was strictly nineteenth-century typology, where nearly every locality produced a different taxon if the looked even slightly different. Frick (1937, p. 20, footnote 2; p. 322) was explicit in stating that many of his “species” were simply convenient labels for specimens from different localities. Apparently, he was unfamiliar with or unaware of the statistical and populational thinking about species that was devel- oping in biology and even in paleontology (e.g., Simpson, 1937) at the same time. To his credit, Frick’s (1937) monograph is beautifully illus- trated and comprehensive, and describes an enormous amount of impor- tant new material that he paid his collectors to find. Frick was one of the first to conceive of the dromomerycines and aletomerycines as a group, and to recognize most of the valid genera within the group. This was no mean feat since most of the work was done at the height of the Great Depression. Janis and Manning (1998, p. 481) noted that “the family is badly in need of revision at the subgeneric and specific levels. Many of these genera are greatly oversplit (most notably Aletomeryx, Rakomeryx, Cranioceras, and particularly Bouromeryx), and some species, espe- cially in the case of the Cranioceratinae, may be assigned to the wrong genus.” Since 1937, no one has attempted a complete revision of the group. A few additional specimens (with two new taxa) were described by Stirton (1936, 1944), Webb (1983), and Whistler (1984). Webb (1969) FIGURE 1. A, Skeleton of Dromomeryx borealis (after Douglass, 1909). B, and Voorhies (1990) discussed the validity of some of Frick’s (1937) Restoration of Dromomeryx borealis (after Scott, 1913). C, Skeleton of taxa. Webb (1983) reviewed the status of Pediomeryx and Yumaceras, Aletomeryx gracilis (after Lull, 1920). the last and most advanced of the cranioceratins, placing the latter taxon as a subgenus of the former. Janis and Manning (1998) provided the first was a pronghorn. Frick (1937) was the first to unite all these previously general overview of the group since Frick (1937), but retained most of described genera, along with all the new taxa he named, as a unified group, Frick’s genera, and did not attempt a revision of the species. In this the Dromomerycinae. Within this subfamily, Frick (1937) recognized paper, we follow the cladistic relationships and generic diagnoses pre- two divisions (a rank between family and subfamily), several tribes, sented by Janis and Manning (1998, fig. 32.3—Figure 2 in this paper), more than a dozen genera, many subgenera, and dozens of species. which was based on a 1980 cladogram by Earl Manning. We focus in- Unfortunately, Frick (1937) did not indicate to which subgenera stead on revising the species within the relatively distinct and clearly his genera were attached, and most of these subgenera are so poorly monophyletic genera. defined, cumbersome, or redundant that they have been ignored by later The familial relationships of the dromomerycines and authors, or treated as genera (e.g., Janis and Manning, 1998). Simpson aletomerycines are also controversial. As noted above, the first known (1945, p. 267, note 1) noted that, “Frick’s taxonomic system is not, and specimens were confused with a variety of ruminants, including bovids, was not intended to be, comparable with that of anyone else. Frick’s cervids, moschids, and antilocaprids. Most early authors (e.g., Cope, 275

FIGURE 2. Phylogenetic relationships of the Dromomerycinae (after Janis and Manning, 1998). Characters given by Janis and Manning, 1998, fig. 32.3.

1878; Douglass, 1909; Matthew, 1924; Frick, 1937; Simpson, 1945) were examined, and most were measured with digital calipers. Specimens considered dromomerycines and aletomerycines to be cervids or cervoids. were photographed with a Nikon 5700 digital camera. In addition, im- However, Stirton (1944) reclassified them as a subfamily of the Euro- portant material from the YPM, YPM(PU), LACM and UNSM collec- pean family Palaeomerycidae, which he allied with the . That tions were also examined and measured. Although skulls and upper den- assignment has been followed by some authors (Crusafont, 1961; Viret, titions were examined when available, most of the statistics were per- 1961; Hamilton, 1978), while others (e.g., Romer, 1966; Leinders, 1983) formed on lower dentitions, since these were the only elements that placed dromomerycines and aletomerycines with the cervoids. Janis and provided a sufficient sample size. Statistical analyses were performed Scott (1987) convincingly showed that dromomerycines and using Excel and Systat software. Modern statistical and populational aletomerycines were cervoids, a sister-taxon to cervids, and that the concepts of species were applied to Frick’s (1937) taxonomy, and coef- similarities to giraffids were plesiomorphic or convergent. Duranthon et ficients of variation (CV) used to decide whether a size cluster is too large al. (1995) described new palaeomerycid material from and , to contain only a single species. Coefficents of variation of most and argued that the horns of palaeomerycids and dromomerycines were species tend to be less than 10, except for sexually dimorphic features non-homologous, and therefore the two groups were not closely related. (Kurtén, 1953; Simpson et al., 1960; Yablokov, 1974). Student’s t-tests However, Janis (2000) showed that the overwhelming majority of the were used to determine whether two populations were statistically dis- characters in dromomerycids support their alliance with palaeomerycids, tinct, and Kologmorov-Smirnov tests were used to determine if the popu- and therefore these differences in horns are probably not significant. lations followed a normal distribution. Dromomerycines and aletomerycines have been raised to the fam- The first question that arises when dealing with taxa that are ily-rank name Dromomerycidae by many recent authors (Hamilton, 1978; largely based on slight size differences is whether some of that size Janis, 1982; Leinders, 1983; Webb, 1983; Stucky and McKenna, 1993; disparity could be due to sexual dimorphism. Nearly all authors have Janis and Manning, 1998), but Janis and Scott (1987) recommended that presumed that skulls with larger horns are from males, analogous to the they be referred to the European family Palaeomerycidae, since situation in the Cervidae and . In some cases (such as the Palaeomeryx is clearly the sister-taxon of the dromomerycines and Aletomeryx Quarry sample, or the Sheep Creek Formation sample of aletomerycines; this was also followed by McKenna and Bell (1997). Sinclairomeryx), there are multiple skulls of both presumed male and Even though the family rank name of Dromomerycidae is widely used in female individuals. The large samples from Aletomeryx Quarry show that the current literature, we agree with Janis and Scott (1987) and McKenna both presumed males and females apparently had horns, while the and Bell (1997) that the more natural grouping should include the North Sinclairomeryx sample seems to show that only presumed males had American dromomerycines and aletomerycines with their Eurasian sis- horns. Apparently, in some groups (such as Aletomeryx), both males and ter-taxa in a single monophyletic family. females had large saber-like canines (usually found only in male hornless METHODS ruminants). However, the majority of dromomerycine taxa lacked large upper canines in either males or females. In all these population samples In this study, all of the dromomerycine specimens in the AMNH where sex can be determined, there are no differences in size or characters 276 of the skeleton other than horns (Lull, 1920; Janis, 2000). Thus, we can point out that it could also be referred to other dromomerycids from this rule out sexual dimorphism as the cause of the majority of the size locality, so this range extension is questionable. In addition, Lull (1920) differences of dromomerycine taxa. and Frick (1937, p. 159-160) say that the material of A. “marshi” is from Once sexual dimorphism has been ruled out, samples that were the “Harrison Formation of Nebraska.” However, it is likely that it is from the same locality were compared to determine the typical range of really from the overlying Runningwater beds in the same area, or possi- variation. These were then amplified by samples from the same age and bly from the latest Arikareean Anderson Ranch Formation of Hunt (2002) region, and finally samples from all regions of the same age. Finally, in (formerly the “upper Harrison beds” of Peterson, 1909). taxa that span a significant temporal interval, samples from each subdivi- sion of a land mammal age were compared to determine if there were Aletomeryx gracilis Lull, 1920 long-term temporal trends. Figures 1C, 3, 4; Table 1 The biostratigraphic assignment of specimens described in this Blastomeryx marshi Lull, 1920 report follows Tedford et al. (1987, 2004), Skinner et al. (1977), and Blastomeryx (Dyseomeryx) marshi Matthew, 1924 Skinner and Johnson (1984). Blastomeryx (Dyseomeryx) scotti Matthew, 1924 Institutional abbreviations: AMNH, American Museum of Aletomeryx marshi Frick, 1937 Natural History, NY; CMNH, Carnegie Museum of Natural History, Aletomeryx scotti Frick, 1937 Pittsburgh, PA; F:AM, Frick Collection, AMNH; DMNH, Denver Aletomeryx lugni Frick, 1937 Museum of Nature and Science, Denver, CO; MCZ, Museum of Com- parative Zoology, Harvard University, Cambridge, mA; TAM, Type specimen—YPM 10732, skull, jaws, and skeleton, from A&M University collection, now at the Texas Memorial Museum, Uni- “Harrison beds” (, early Hemingfordian, fide versity of Texas, Austin. TX; UCMP, University of California Museum Tedford et al., 1987, p. 167), Nebraska. of Paleontology, Berkeley, CA; UCR, University of California, River- Referred material—Hundreds of specimens from Aletomeryx side, collections (now housed at UCMP); UF, Florida Museum of Natu- Quarry, Frick Dunlop Camel Quarry, and many other Runningwater ral History, University of Florida, Gainesville, FL; SDSM, South Da- quarries in the YPM, F:AM, AMNH, and UNSM collections (many kota School of Mines Museum, Rapid City, SD: UNSM, University of listed by Frick, 1937, pp. 157-159). Nebraska State Museum, Lincoln, NE; USNM, National Museum of Distribution—From the early Hemingfordian “Marsland” For- Natural History, Smithsonian Institution, Washington, DC; YPM, Yale mation (probably Runningwater Formation) and possibly the latest Peabody Museum, New Haven, CT; YPM(PU), Princeton University Arikareean Harrison or “upper Harrison” (Anderson Ranch Formation collections, now housed at YPM. of Hunt, 2002), western Nebraska; early Hemingfordian Martin Canyon Other abbreviations: CV = coefficient of variation; l.f. = local Formation of Colorado. fauna. Diagnosis—Medium- to small-sized species of Aletomeryx (see Table 1). SYSTEMATIC PALEONTOLOGY Description—The large samples from Aletomeryx Quarry and Class Mammalia Linnaeus, 1758 other Runningwater localities were fully described by Lull (1920) and Frick (1937). Order Artiodactyla Owen, 1848 Discussion—Aletomeryx gracilis was described by Lull (1920) Family Palaeomerycidae Lydekker, 1883 based on hundreds of excellent specimens from Aletomeryx Quarry in the Subfamily Aletomerycinae Frick, 1937 “Harrison beds” (early Hemingfordian Runningwater Formation, fide Diagnosis—Mesodont molars, with cingulae and Palaeomeryx Tedford et al., 1987, p. 167), Cherry County, Nebraska. Lull (1920) thoroughly described both male and female specimens of this species, fold (a ridge on the labial side of the protoconid that extends posteromedially) reduced or lost, upper canine reduced, upper premolar and numerous other excellent male and female skulls, jaws, and postcranials were described by Frick (1937). Compared to other dromomerycids, protocone reduced, orbit moved posteriorly (anterior rim over M3), older females with small supraorbital horns, ramus deeper, premolars Aletomeryx gracilis is one of the best-known species, with hundreds of specimens in many different collections, and mounted specimens on reduced, antorbital vacuity present, metapodials lengthened (after Janis and Manning, 1998, p. 480). display at the YPM, at the Trailside Museum in Fort Robinson, Ne- braska, and elsewhere. Aletomeryx Lull, 1920 Lull (1920, p. 125) described another specimen (YPM 10756, from the “Harrison beds,” Nebraska, probably early Hemingfordian) Type species—Aletomeryx gracilis Lull, 1920 consisting of a skull and jaws and partial skeleton, which he named Included species—A. marslandensis Frick, 1937, A. occidentalis Blastomeryx marshi. The skull had no horn bases, but large canine tusks, Whistler, 1984 giving Lull the impression that it belonged to Blastomeryx. However, he Distribution—-?Latest Arikareean, Nebraska; early noted (p. 125) that it was also the size and morphology of some of his Hemingfordian, Colorado and California; early to ?late Hemingfordian, female specimens of Aletomeryx gracilis. Matthew (1924) referred this Nebraska; material to Blastomeryx (Dyseomeryx) marshi. Frick (1937, p. 159) com- Diagnosis—Short horns (no more than one-third skull length) pared this specimen to the many female skulls of A. gracilis in his that are fairly upright; posteromedial corner of horn has a narrow vane, collection, and correctly concluded that “Blastomeryx” marshi was a separating it from the posteroinferior border of the orbit. Smaller horns female specimen of A. gracilis. in females. Short nasals. Longest and most slender metapodials of all Blastomeryx (Dyseomeryx) scotti was named by Matthew (1924, dromomerycids. Small body size (modified from Janis and Manning, p. p. 193) based on MCZ 17743, a fragment of frontal horn, from the 482). “Loup Fork” of Nebraska (probably early Hemingfordian Runningwater Discussion—Nearly all known specimens of Aletomeryx are from Formation, fide Tedford et al., 1987). This specimen was first mentioned the early Hemingfordian of Nebraska, and a few are from the early by Scott (1890, p. 76) in his discussion of Cope’s genus Blastomeryx. Hemingfordian Martin Canyon Formation of Colorado. In addition, there Frick (1937, p. 152) noticed that it bore a resemblance to the horn cores is A. occidentalis from the early Hemingfordian of California. Janis and in his Aletomeryx collection, but that it was from an individual slightly Manning (1998, p. 482) note there is a possible late Hemingfordian larger than typical A. gracilis. No other material was referred to this specimen from the Sheep Creek Formation of Nebraska, although they species by Frick (1937, p. 161), although in the AMNH and other collec- 277

FIGURE 4. Bivariate plot of m1-3 length vs. p2-4 length of selected specimens of Aletomeryx. Solid triangles = type and referred specimens of A. gracilis; x = type and referred specimens of A. scotti; open squares = specimens of A. occidentalis; open diamond = type specimen of A. “marshi”; X with vertical slash = specimens of A. marslandensis. m1-3 length of 40 mm is within the range of variation of A. gracilis (Fig. 4). Thus, since the type material is undiagnostic and its size is within the range of A. gracilis, we regard it as a junior synonym of that taxon. Aletomeryx marslandensis Frick, 1937 Figures 3, 4; Table 1 Type specimen—UNSM 50-28-8-34, top of cranium, from the early Hemingfordian “Marsland” Formation (probably Runningwater Formation), Nebraska. Referred specimens—UNSM 1-11-8-36, skull, mandible, and skeleton (“?Aletomeryx marslandensis Var.” of Frick, 1937, p. 163); UNSM 1-13-6-35, female skull and mandible; numerous other UNSM specimens listed by Frick (1937, pp. 162-163). Diagnosis—“Larger than A. gracilis and smaller than S. riparius” FIGURE 3. Specimens of Aletomeryx gracilis. F:AM 32310, 32334, 32324, (Frick, 1937, p. 162). Horns taller than those of A. gracilis. The p4 tends and 32322 are presumed females; the rest are of males (e.g., F:AM 32300, to be large relative to the much reduced p2-3. 32303). UNSM 50-28-8-34 is the holotype of A. marlandensis. (after Distribution—From the early Hemingfordian “Marsland” For- Frick, 1937, fig. 16, p. 146). mation (probably Runningwater Formation), Box Butte and Dawes coun- tions, the name “scotti” has been attached to the larger specimens of A. ties, Nebraska. gracilis. Webb (1969) and Janis and Manning (1998) maintained the Description—No new material has been found since the descrip- name Aletomeryx scotti for larger individuals of A. gracilis. tions of Frick (1937, p. 162). In our data set, large numbers of jaws (the most common element) Discussion—Frick (1937) based the species Aletomeryx of specimens referred to Aletomeryx were measured and plotted (Fig. 4). marslandensis on UNSM 50-28-8-34, a cranial fragment from the Although the specimens referred to A. scotti plot at the larger end of the “Marsland” Formation of Box Butte County, Nebraska (early size distribution, the cluster of points is continuous and there is no clear Hemingfordian). He referred numerous other specimens in the UNSM break between A. scotti and smaller A. gracilis. Nor can the difference be collections to that species. His diagnosis was based largely on size, and due to sexual dimorphism, because there are both male and female skulls on horns that tended to be taller than A. gracilis, and also based on the assigned to the A. gracilis and A. scotti size clusters. Although this size reduction of p2-3. spread appears impressive when examining specimens in cabinets, sta- Our data (Fig. 4) show that the specimens referred to A. tistically it is not large. The CVs of nearly every dental variable are marslandensis do tend to be among the largest in the sample, with some between 4 and 6, which is within the range of variation of a single species of the most reduced premolar rows (relative to size) of all known (Table 1). Thus, we see no reason to retain the difficult distinction be- Aletomeryx. Although the separation between the A. marslandensis speci- tween small A. gracilis and large A. scotti, and regard them as a single mens and the A. gracilis/scotti cluster is slight, they are discrete enough species, A. gracilis. to retain as a distinct species. Aletomeryx lugni was named by Frick (1937, p. 161) based on Aletomeryx occidentalis Whistler, 1984 UNSM 13-1-17-32, a right ramus with p2-p4 alveoli and m1-3 from Figures 4, 5; Table 1 Bridgeport Quarries (early Hemingfordian), Morrill County, Nebraska. Frick (1937, p. 162) provided no diagnosis other than it approximated Type specimen—UCR 10335, right ramus with p2-m3, from the “smaller specimens of Sinclairomeryx riparius from Snake Creek.” The early Hemingfordian Boron l.f., Kern County, California. type is a poor specimen with no preserved premolars. Nevertheless its Referred specimens—Material listed by Whistler (1984, p. 25). 278 TABLE 1. Measurements of various dromomerycine and aletomerycine taxa (in mm). Number in parentheses = sample size. 279 TABLE 1 continued

Diagnosis—Larger than A. marslandensis, but smaller than all gate, with paired nasal bosses in males, and deep maxillary pits. Unworn Sinclairomeryx, with large p2; unreduced lower premolars, with more molars may retain a weak Palaeomeryx fold. More brachyodont molars complicated crown pattern than found in other species of Aletomeryx, than Aletomeryx, metapodials more heavily proportioned (modified from and with relatively expanded metaconid; hypostylid of p3-4 expanded Janis and Manning, 1998, p. 482). into a distinct cuspid that connects to the hypoconid with a short crest; Distribution—Late Hemingfordian-early Barstovian, Nebraska well-developed metaconid on p4; anteriolabial buttress and anterior cin- and Saskatchewan. gulum on m2; hypoconulid crescent on m3; and many other characters Discussion—Stirton (1944, p. 640) suggested that Sinclairomeryx cited in Whistler (1984, p. 25). Frick, 1937 was a junior synonym of Matthew’s (1924) subgenus Distribution—Known only from the type locality. Dyseomeryx. However, Matthew (1924) referred several different taxa Description—No additional material has been reported since the to Dyseomeryx, including Blastomeryx (Dyseomeryx) marshi and descriptions of Whistler (1984). Blastomeryx (Dyseomeryx) scotti, both of which are here referred to Discussion—Whistler (1984) described the species A. occidentalis Aletomeryx gracilis, and Blastomeryx (Dyseomeryx) sinclairi, which is based on fragmentary specimens from the early Hemingfordian Boron referable to Rakomeryx, not Sinclairomeryx. In addition, most of l.f., Kern County, California. Although the material consisted mostly of Matthew’s type specimens were undiagnostic fragmentary dental re- jaw fragments, there was a broken horn base in the collection (Fig. 5C) mains that are only doubtfully referable to Sinclairomeryx. Thus, the that demonstrated clearly the Aletomeryx affinities of the material. As name Sinclairomeryx is the first available generic name that can be ap- Whistler (1984) noted, this taxon is larger than A. marslandensis, but plied to the material discussed below. smaller than the much larger taxon Sinclairomeryx. In our data set, the specimens clearly plot on the large end of the size distribution, and seem Sinclairomeryx riparius (Matthew, 1924) disjunctly larger, without the premolar reduction seen in M. marslandensis Figure 6 (Fig. 4). This size distinction, in addition to the more subtle dental Blastomeryx (Dyseomeryx) riparius Matthew, 1924 characters listed by Whistler (1984), plus its geographic isolation from Sinclairomeryx riparius Frick, 1937 the Great Plains species of Aletomeryx, seem to justify retention of this Sinclairomeryx sinclairi Frick, 1937 species. Sinclairomeryx tedi Frick, 1937 Sinclairomeryx Frick, 1937 Type specimen—AMNH 18956, left maxilla with P2-M3 (Fig. Blastomeryx Matthew, 1924 (in part) 6A), from Thomson Quarry, Stonehouse Draw, late Hemingfordian Sheep Sinclairomeryx Frick, 1937 Creek Formation, Sioux County, Nebraska. Referred material—Numerous specimens listed by Frick (1937, Type and only species—Sinclairomeryx riparius (Matthew, 1924) p. 164-168), all from the late Hemingfordian Sheep Creek Formation, Diagnosis—Male supraorbital horns long, projecting anteriorly Nebraska. and laterally. Antorbital vacuity and lacrimal fossa present. Nasals elon- Diagnosis—Same as for genus. 280 ately twisted with bulbous tips, flattened anteroposteriorly. Dentition similar to Dromomeryx, but open anterior fossette on p4. Limbs moder- ately heavily proportioned. Females may have also had horns (modified from Janis and Manning, 1998, p. 482). Distribution—Early Barstovian, Nebraska and Texas. Drepanomeryx falciformis Sinclair, 1915 Drepanomeryx falciformis Sinclair, 1915 Drepanomeryx (Drepanomeryx) falciformis Frick, 1937 Drepanomeryx (Matthomeryx) matthewi Frick, 1937 Type specimen—YPM(PU) 12072, left horn (Fig. 7A), from FIGURE 5. Material of Aletomeryx occidentalis. A-B, UCR 10335, holotype “Snake Creek” beds (West Sinclair Draw, early Barstovian Olcott For- right ramus in labial and occlusal view. C, UCR 10348, right horn fragment. mation, fide Skinner et al., 1977, p. 349), Nebraska. (after Whistler, 1984, figs. 51, 52, 57, p. 28). Referred material—Numerous specimens listed by Frick (1937, Distribution—Most of the referred material is from the middle- p. 140-141). All are from the early Barstovian Olcott Formation of late Hemingfordian Box Butte and Sheep Creek formations and equiva- Nebraska (mostly Mill Quarry in Sioux County) or early Barstovian lents, western Nebraska. According to Janis and Manning (1998, p. 482), Sand Canyon Formation in Dawes County (mostly Observation Quarry), there may also be specimens from the early Barstovian Olcott Formation or the early Barstovian Fleming Formation (Trinity River Pit 1) of Texas. of Nebraska, the late Hemingfordian Topham l.f. of the Cypress Hills, Diagnosis—Same as for genus. Saskatchewan, and the early Barstovian Wood Canyon Formation, Distribution—Same as for genus. Saskatchewan (Storer, 1975). Discussion—Sinclair (1915) named Drepanomeryx falciformis Discussion—Blastomeryx (Dyseomeryx) riparius was described based on a broken left horn (Fig. 7A) from the “Snake Creek” beds by Matthew (1924, p. 197), based on AMNH 18956, a left maxilla with (actually early Barstovian Olcott Formation, fide Skinner et al., 1977, p. P2-M3, from Stonehouse Draw in the late Hemingfordian Sheep Creek 349) with a distinctive distally widened tips, flattened ovoid profile and Formation (Fig. 6A). Based on such limited material, Matthew (1924) anterodorsal curvature. Frick (1937, p. 140) erected a separate subgenus, could only compare it with the better known genus Blastomeryx, but it Drepanomeryx (Drepanomeryx) falciformis, for this specimen, and de- was clearly larger than any other Blastomeryx species then known. Frick scribed additional material, including partial skulls, jaws, and skeletal (1937, p. 165) referred this specimen to his large sample of Sinclairomeryx elements. Frick gave no diagnosis for the subgenus, and it is unclear why specimens from the same quarry in Stonehouse Draw. He noted only a subgenus was necessary, since it is monotypic. It seems likely that that S. riparius was slightly smaller than the type skull of S. sinclairi, Frick’s reason for the subgenus might have been the morphological dif- but were otherwise very similar. ferences between the two species, but these reasons are no longer appli- Frick (1937, p. 165) named another species, Sinclairomeryx cable in modern systematics. sinclairi, based on F:AM 33791 (Fig. 6B), a complete male skull with the Frick (1937, p. 141) named another new subgenus and species, distinctive, forwardly-curved horns with terminal knobs from Thomson Drepanomeryx (Matthomeryx) matthewi, based on F:AM 33740, a cra- Quarry in the late Hemingfordian Sheep Creek Formation, Nebraska. He nial fragment with spectacular curved horns (Fig. 7B) from Observation referred additional material to this species, but did not provide a diagno- Quarry in the early Barstovian Sand Canyon Formation. Once again, sis or any way of distinguishing it from S. riparius. In fact, the speci- Frick (1937) created a monotypic subgenus, so it is not clear why it was mens referred to S. sinclairi completely encompass the variation seen in necessary to erect subgenera to distinguish the two recognized species of S. riparius, so there is no valid size distinction between the two taxa. Drepanomeryx. Frick’s (1937, p. 138) discussion separated Since the type of S. riparius is so poor, we cannot see any basis for Drepanomeryx (Matthomeryx) matthewi based on the fact that the horns maintaining two species based on the referred material. narrow distally, rather than expand distally. Janis and Manning (1998, p. Sinclairomeryx tedi was named by Frick (1937, p. 168) based on 483) followed this diagnosis, but argued that D. (M.) matthewi “differs in a right ramus (Fig. 6E-F) with p2-m3 (F:AM 32875) from Ginn Quarry possession of cranial appendages that are narrowed distally, rather than in the Sheep Creek Formation, Dawes County, Nebraska. Frick (1937, p. expanded. Premolars more reduced and diastemata longer than in D. (D.) 168) compared it to Barbouromeryx trigonocorneus and Aletomeryx and falciformis.” Bouromeryx, but not to any Sinclairomeryx species, yet he placed it in We examined the specimens referred to both of these subgenera that genus. The type material consists mostly of rami and a few maxillae, and species, and we are not convinced that they are truly distinct. Al- and differs from typical S. riparius only in that it is slightly smaller. though their horns vary in shape and in the taper from proximal to distal However, it is entirely within the range of size of specimens referred to ends, the available sample shows considerable variation in the shape of S. sinclairi, so we regard it as a junior synonym of S. riparius. the horns (in addition to differences caused by postmortem deforma- tion). We are not convinced that such variation is not within that found in Subfamily Dromomerycinae Frick, 1937 normal populations. Given that cervoid antlers, antilocaprid horn cores, Tribe Dromomerycini Frick, 1937 and bovid horns are notoriously variable due to aberrations in growth, we think that the single odd-shaped distally expanded horn of the type Discussion—Janis and Manning (1998, p. 482) provide a thor- specimen of D. falciformis might simply be due to deformed growth of ough discussion and diagnosis of the subfamily Dromomerycinae, and that individual. Many years of collecting in these beds has not produced the tribe Dromomercyini, so it will not be necessary to repeat that another specimen like the type of D. falciformis, but the Frick Collection information here. has a number of specimens like those referred to D. (M.) matthewi. Drepanomeryx Sinclair, 1915 Janis and Manning (1998, p. 483) also distinguished the taxa by Figures 7-8; Table 1 characters in their lower jaws (reduction in premolars and diastema). We measured all the available specimens, and the single lower jaw referred to Type and only species—Drepanomeryx falciformis Sinclair, 1915 D. (D.) falciformis falls within the small end of the size range (Fig. 8) of Diagnosis—Supraorbital horns elongated and posteriorly di- D. (M.) matthewi. The coefficient of variation (Table 1) of the total rected, with small basal flanges; shafts widely bowed inwardly, moder- sample is within 4 to 6 on all dental variables, so it is consistent with the 281

FIGURE 6. Sinclairomeryx riparius. A, Type maxilla, AMNH 18956. B, Type skull of S. sinclairi, F:AM 33791, in anterior view. C-D, Hornless female skull of S. riparius, F:AM 33790. E-F, Type specimen of S. tedi, F:AM 32875, in lateral and occlusal view. Scale bar in cm. hypothesis that it is from a single species. The symphysis and diastema P4. Limb proportions like that of Drepanomeryx (after Janis and Man- referred to D. (D.) falciformis is indeed short, but there are specimens of ning, 1998, p. 483). D. (M.) matthewi that are shorter. Rakomeryx sinclairi (Matthew, 1918) In short, we see no basis for two separate species or subgenera of Drepanomeryx. We refer all specimens of this genus to a single species, Cervavus sinclairi Matthew, 1918 D. falciformis. Blastomeryx (Dyseomeryx) sinclairi Matthew, 1924 Dromomeryx near borealis Gazin, 1932 (in part) Rakomeryx Frick, 1937 Rakomeryx raki Frick, 1937 Figures 9-10; Table 1 Rakomeryx jorakius Frick, 1937 Rakomeryx yermonensis Frick, 1937 Type and only species—Rakomeryx sinclairi (Matthew, 1918) Cranioceras unicornis Frick, 1937 (in part) Distribution— Late Hemingfordian of Florida, Montana, Cali- Rakomeryx gazini Frick, 1937 fornia, and Nebraska; early Barstovian, Nebraska and California; late Rakomeryx sinclairi Skinner et al, 1977 Barstovian of Oregon and Montana (see Janis and Manning, 1998, p. Rakomeryx sinclairi Janis and Manning, 1998 483, for localities). Diagnosis—Horns with less pronounced basal flange, anteriorly Type specimen— AMNH 18879, a partial skull (Fig. 9A) from directed, with bases strongly flattened anteroposteriorly, attenuated at the early Barstovian Olcott Formation (Skinner et al., 1977), Nebraska. tips; shafts strongly bowed laterally, forming concave half-moon shape Referred specimens—Material listed by Frick (1937, p. 101- when viewed from front. Orbits shifted posteriorly over anterior M3. 107). Premolars more reduced than in Dromomeryx, but p4 may lack closure Diagnosis—Same as for genus. of anterior fossette. Metastylids on upper molars, and large metacone on Distribution—Same as for genus. 282

FIGURE 8. Plot of p2-4 vs. m1-3 of specimens of Drepanomeryx. Solid diamonds = specimens referred to D. (Matthomeryx) matthewi; open square = specimen referred to D. (D.) falciformis. found in the early Barstovian of the Mojave Desert. Rakomeryx jorakius was named by Frick (1937, p. 105), based on F:AM 31332, a crushed posterior cranium and associated dentition, from the early Barstovian Green Hills Division in the Barstow Formation (Fig. 9C). Frick (1937) assigned no other material to this species nor did he provide a diagnosis of this species. Examining the type material, it is based on a very large individual of Rakomeryx with heavier horns than the type specimen of R. raki, but there is no basis for making it a distinct species. Thus, we synonymize it with Rakomeryx sinclairi. Rakomeryx yermonensis was named by Frick (1937, p. 105) based on F:AM 31800, a mandible (Fig. 9D), from a quarry 5 miles east of Yermo, California. Additional material from this quarry was also referred to this species. Frick (1937, p. 100) provided no diagnosis for the spe- cies, except to state that “the premolars are slender and somewhat differ- ent, particularly as seen in the p3” from the Barstow sample. Examining the type specimen (Fig. 9D), we find no features to distinguish it from typical R. sinclairi other than its small size (Fig. 10). However, this size FIGURE 7. Drepanomeryx falciformis. A, YPM(PU) 12072, type specimen is within the small end of the size range of typical R. sinclairi, and the of D. falciformis, left horn. B, F:AM 33740, type specimen of D. coefficient of variation of the R. sinclairi samples is between 5 and 7 for (Matthomeryx) matthewi, horns and skull. Scale bar in cm. all dental measurements (Table 1), so there is no justification for retaining Description—Most of the material of Rakomeryx was described R. yermonensis. The alleged slenderness of the premolars is also within by Frick (1937). the normal range of variation of R. sinclairi, and the vague reference to the Discussion— Cervavus sinclairi was named by Matthew (1918, p3 being “somewhat different” is useless in diagnosing a taxon. p. 218) based on AMNH 18879, a ramus (Fig. 9A) from the early Rakomeryx gazini was erected by Frick (1937, p. 106) based on Barstovian Olcott Formation (Skinner et al., 1977). It was reassigned to LACM (CIT) 351, partial left horn core, from the early Barstovian Skull Blastomeryx (Dyseomeryx) sinclairi by Matthew (1924, p. 198). It was Spring l.f., southeast Oregon. It was originally described and figured by then transferred to Cranioceras unicornis by Frick (1937, p. 82), and Gazin (1932, p. 82), but Gazin referred it to Dromomeryx near borealis, Webb (1969) followed that synonymy. However, Skinner et al. (1977, p. even though he commented that the horn was more robust and curved 349) transferred it to Rakomeryx based on detailed comparison of Frick than in typical Montana Dromomeryx borealis. Frick (1937, p. 107) specimens of Cranioceras and Rakomeryx (particularly since Cranioceras transferred this specimen (and the remaining referred material described is unknown from the early Barstovian), and this was followed by Janis by Gazin, 1932) to Rakomeryx, and erected the new taxon, R. gazini, and Manning (1998). without any diagnosis, other than reference to Gazin’s (1932) com- Frick (1937, p. 101) named Rakomeryx raki for the distinctive ments. Shotwell (1968) placed this taxon in Dromomeryx borealis. We dromomerycine with the bowed horns from the Barstow Formation. The have examined this material, and find no obvious differences from the type was designated as F:AM 31320, the top of a cranium (Fig. 9B), material now referred to R. sinclairi. Thus, R. gazini is here considered a from the early Barstovian Green Hills Division, Barstow, California. junior synonym of R. sinclairi. Frick (1937, p. 101) referred material described as “Dromomeryx or Dromomeryx Douglass, 1909 Cervus?” (Merriam, 1919, p. 524) to this species. Examining the type Figures 1A-B, 10-11; Table 1 material (Fig. 9B), it is clear that it completely overlaps the size range (Fig. 10) of specimens referred to R. sinclairi. Since we cannot find any Type and only species—Dromomeryx borealis (Cope, 1878) other diagnostic characters to maintain its distinctiveness, we synony- Diagnosis—Horns large and broad, forwardly directed (forming mize the two taxa, and Frick’s (1937) type species for the genus Rakomeryx, an angle of 60 degrees with the nasals) and somewhat laterally bowed; R. raki, becomes a junior synonym of the older taxon sinclairi. prominent lateral basal flange, and deeply grooved on the anterolateral Frick (1937, p. 105) named two other species of Rakomeryx, also face. Orbit moved posteriorly (anterior rim over posterior M3). Shallow 283

FIGURE 10. Bivariate plot of m1-3 length vs. p2-4 length of specimens of Subdromomeryx, Dromomeryx, and Rakomeryx. Open triangles = S. scotti; solid triangle = type of S. wilsoni; open diamond = type of D. borealis; open circles = D. whitfordi; solid circles = D. pawniensis; solid squares = R. yermonensis; open squares = R. raki; solid diamonds = R. sinclairi; x = type of R. kinseyi.

(Subdromomeryx) based on the larger and smaller size clusters of Dromomeryx. He also oversplit Dromomeryx into numerous species based on inadequate comparisons with no diagnoses. We find that there is a clearly defined larger size group, D. borea- lis, and a smaller species, Subdromomeryx scotti with a possible second Subdromomeryx species, S. antilopinus (Fig. 10). There is no evidence for any other valid species among all the many named dromomerycines. Nor is there any justification for two separate subgenera for essentially two monotypic genera. Thus, we reject the unnecessary subgenera D. (Dromomeryx) and D. (Subdromomeryx) in favor of two genera, Dromomeryx and Subdromomeryx (the latter elevated to generic rank). Dromomeryx borealis (Cope, 1878) Blastomeryx borealis Cope, 1878 Palaeomeryx borealis Douglass, 1903 Palaeomeryx borealis Matthew, 1904 Blastomeryx borealis Matthew, 1908 FIGURE 9. Rakomeryx sinclairi. A, AMNH 18879, type specimen of R. Blastomeryx borealis Matthew and Cook, 1909 sinclairi (after Matthew, 1918, fig.17). B, (left) F:AM 31320, type specimen Palaeomeryx borealis Matthew, 1909 of R. raki. and (right) F:AM 31332, type specimen of R. jorakius. (after Dromomeryx borealis Douglass, 1909 Frick, 1937, fig. 13). C, F:AM 31880, type specimen of R. yermonensis. Dromomeryx whitfordi Sinclair, 1915 (Photo by D. Prothero). Scale bar in cm. Dromomeryx pawniensis Frick, 1937 lacrimal fossa. Lower p4 with anterior fossette closed by anterior exten- Type specimen—AMNH 8132, cranium with left horn and cheek sion of metaconid (modified from Janis and Manning, 1998). teeth, from the early Barstovian Deep River beds, Montana Distribution—Compared to most other dromomerycines, D. Referred specimens—Most of the known material was listed borealis was very widespread in North America through much of the by Frick (1937, p. 114-122). Miocene. Its distribution includes the late Hemingfordian of Nebraska, Diagnosis—Same as for genus. early Barstovian of Montana, Oregon, Nebraska, Colorado, Nevada, and Distribution—Late Hemingfordian: Box Butte and Sheep Creek New Mexico; late Barstovian of Nebraska, Colorado, Wyoming, Nevada, Formations, Nebraska; Early Barstovian: Fort Logan Formation, Deep and California; and early Clarendonian of South Dakota and California River beds, Montana; Sixmile Creek Formation, Montana; Flint Creek (see Janis and Manning, 1998, p. 484). beds, Montana; Barnes Creek beds, Montana; Chalk Cliffs l.f., Hepburn Discussion—Dromomeryx is a very abundant and well-known Mesa Formation, Montana; Mascall Formation, Oregon; Beatty Buttes, Barstovian taxon, based on numerous complete and partial skeletons and Oregon; Skull Springs fauna, Oregon; Sucker Creek Fauna, Oregon; Quartz excellent skulls and jaws from both Montana and the Great Plains. It was Basin fauna, Oregon; Olcott Formation and Sand Canyon beds, Ne- the first genus to be distinguished from the wastebasket usage of late braska; Virgin Valley Formation, Washoe Formation, Nevada; Skull Ridge nineteenth-century taxa such as Cosoryx, Blastomeryx and Palaeomeryx, Member, Tesuque Formation, New Mexico; Lower Pawnee Creek fauna, based on Douglass’ (1909) description of much more complete material Colorado; Late Barstovian: Cornell Dam Member, Valentine Formation, than was available to Cope, Matthew, Cook, and Douglass before 1909. Nebraska; Upper Pawnee Creek Fauna, Colorado; Gravel Quarry, Goshen Frick (1937) split off the subgenera D. (Dromomeryx) and D. Hole, Wyoming; Stewart Spring/Tonopah l.f., Nevada; Barstow Forma- 284 show that D. pawniensis is within the same size range as the type of D. borealis, so there is no clear basis for defining the species other than D. pawniensis comes from the Pawnee Creek Formation of Colorado, and D. borealis is primarily from Montana. Since their geographic differ- ences are not distinguished by any obvious morphological or size differ- ences, we synonymize D. pawniensis with D. borealis. Sinclair (1915, p. 94) named Dromomeryx whitfordi, based on YPM(PU) 12054, partial left and right horns (Fig. 11C), from West Sinclair Draw in the early Barstovian Olcott Formation, Sioux County, Nebraska (Skinner et al., 1977). He distinguished this species from D. borealis by having “horn bases about one third wider than D. borealis, with the posterior upper corner of the wing-like expansion at the base of the horn sharply angular instead of a flowing curve as in D. borealis” (Sinclair, 1915, p. 94-95). Matthew (1924, p. 72) referred this material to D. borealis. Frick (1937, p. 117) restored the taxon D. whitfordi, and referred much additional material from his collection from the Olcott Formation to this taxon. However, he provided no additional diagnosis, and the only obvious distinction is that D. whitfordi is from Nebraska, while his D. pawniensis is from Colorado and D. borealis from Montana. We measured a large number of referred specimens from the Frick Collec- tion (Fig. 10) and found that they are in the same size range as D. borealis or D. pawniensis, nor is there any other morphological feature which distinguishes these samples. In addition, Sinclair’s (1915) supposed dif- ferences in the type horn core of D. whitfordi from D. borealis are now completely subsumed within the range of variation of horn cores now in the collections. Thus, we place D. whitfordi in synonymy with D. bo- realis. Subdromomeryx (Frick, 1937), new rank Blastomeryx Scott, 1893 (in part) FIGURE 11. Dromomeryx borealis. A, Referred skull and jaws of D. borealis, Dromomeryx Scott, 1913 (in part) CMNH 827 (after Douglass, 1909, plate LIX); B, Type specimen of D. Dromomeryx (Subdromomeryx) Frick, 1937 pawniensis (F:AM 31297). Scale bar in cm. C, Type horn core of D. Cranioceras Frick, 1937 (in part) whitfordi, YPM(PU) 10254 (after Sinclair, 1915, fig. 17). Rakomeryx Tedford et al., 1987 (in part) Rakomeryx Janis and Manning, 1998 (in part) tion, California; Early Clarendonian: Avawatz Formation, California; Ash Dromomeryx (Subdromomeryx) Janis and Manning, 1998 Hollow Formation, South Dakota (after Janis and Manning, 1998, p. 484). Type species—S. scotti (Frick, 1937). Description—Frick (1937) and Douglass (1909) described es- Included species—S. antilopinus (Scott, 1893). sentially all the known material of D. borealis. Diagnosis—Similar to Dromomeryx, but much smaller size (Table Discussion—Cope (1878, p. 222) briefly described AMNH 8132, 1; Fig. 10); molars more mesodont; premolar row shorter, and Palaeomeryx a cranium with left horn and cheek teeth from the early Barstovian Deep fold usually lost. Supraorbital horns relatively smaller, with basal flange River beds, Montana, and gave it the name Blastomeryx borealis. At this less pronounced, and limbs relatively longer and more slender than those time, Cope used the genus Blastomeryx for nearly all specimens of primi- of Dromomeryx (after Janis and Manning, 1998, p. 483). tive cervoids from the early and middle Miocene. Eventually, the genus Distribution—Late Hemingfordian of Nebraska and Nevada; early Blastomeryx was restricted to the hornless , the Barstovian of Texas. Blastomerycinae, when the distinction between dromomerycids and Discussion—As discussed above, the smaller materials referred moschids became more apparent with better specimens. to Dromomeryx (Subdromomeryx) by Frick (1937) are distinct in size Douglass (1903) described additional material of Cope’s (1878) and morphology from Dromomeryx (Dromomeryx), and there seems to species as Palaeomeryx borealis, correctly realizing that this taxon was be no justification for subgenera when there are so few species in each assignable to the Palaeomerycidae, not the . Matthew (1908, genus and subgenus. Instead, we elevate Subdromomeryx from subgeneric p. 546) and Matthew and Cook (1909, p. 408) returned the taxon to to generic rank, in parallel with Dromomeryx, its sister taxon (Fig. 2). Blastomeryx, but Matthew (1909, p. 115) reversed his position and placed it in Palaeomeryx. In the same year, Douglass (1909) published Subdromomeryx antilopinus (Scott, 1893) much more complete material of the taxon from the Barstovian of Mon- Figures 10, 12; Table 1 tana, including a nearly complete skeleton (Fig. 1A) and a much better Blastomeryx antilopinus Scott, 1893 skull than the holotype (Fig. 11A). On this basis, he erected the new Dromomeryx antilopinus Scott, 1913 genus Dromomeryx for some of the material that had previously been Dromomeryx (Subdromomeryx) scotti Frick, 1937 assigned to Blastomeryx and Palaeomeryx. Dromomeryx wilsoni Frick, 1937 Frick (1937, p. 115) named the new taxon Dromomeryx pawniensis, Cranioceras kinseyi Frick, 1937 based on F:AM 31297, the top of cranium with partial horns (Fig. 11B), Rakomeryx kinseyi Tedford et al., 1987 from Barstovian of Pawnee Buttes, Colorado. He referred a number of Rakomeryx kinseyi Janis and Manning, 1998 additional specimens from the late Barstovian Frick Horse and Mast- odon Quarry (Tedford, 1999) to this taxon, but provided no diagnosis. Type specimen—YPM(PU) 10401, partial skull and skeleton, Our measurements of a large number of referred specimens (Fig. 10) from the Deep River beds, Montana. 285

FIGURE 12. Subdromomeryx antilopinus. A, Type specimen of S. antilopinus, YPM(PU)10401 (after Frick, 1937, fig. 14A). B, Type specimen of Subdromomeryx scotti (F:AM 33758). C-E, Excellent referred skull of Subdromomeryx scotti (F:AM 33757) in dorsal, lateral, and palatal views. F, Type specimen of S. wilsoni (F:AM 33800). Scale bar in cm. Diagnosis—Same as for genus sis, nor any criteria to distinguish it from S. scotti. The known measure- Distribution—Same as for genus. ments of the specimen (m1-3 length = 44 mm) do not distinguish it from Description—All known material of S. antilopinus was described S. scotti as currently defined, and it lies completely within the size by Frick (1937). distribution of S. scotti (Fig. 10). Nor can we find any consistent mor- Discussion— Scott (1893, 1895) described Blastomeryx phological difference between the material of S. antilopinus and of S. antilopinus based on YPM(PU) 10401, partial skull and skeleton, from scotti, given the intrapopulational variability typical of dromomerycines. the late Hemingfordian Deep River beds, Montana. Scott’s (1893, p. Thus, we consider S. antilopinus to be the senior synonym of all the 662) original description gave no figures or type specimen, and the diag- Subdromomeryx species. nosis consisted only of “size decidedly smaller than that of B. borealis Frick (1937, p. 123) described S. scotti, based on F:AM 33758, a Cope, and ribs of external crescents on upper molars less prominent.” nearly complete skull (Fig. 12B-E). He provided no diagnosis of this Fortunately, Scott (1895) provided good figures and a much more de- taxon, but based on the referred material, it was largely diagnosed on size. tailed description and diagnosis, so this potential nomen nudum was Numerous excellent skulls and jaws and partial skeletons were listed by validated. In 1913, Scott transferred this species to Dromomeryx. Frick Frick (1937, p. 123-126), nearly all from the Frick Greenside and Thomson (1937, p. 123) recognized this species, but did not provide any diagno- Quarries in the Sheep Creek Formation, Sioux County, Nebraska. 286 Frick (1937, p. 126) erected another species, S. wilsoni (Fig. 12F), Distribution—Latest Arikareean Anderson Ranch Formation (= based on a posterior portion of a skull (F:AM 33800) with both horns “upper Harrison” of Peterson, 1909), Nebraska; early Hemingfordian from the Thomson Quarry in the Sheep Creek Formation, Sioux County, Runningwater (“Marsland”) Formation, Nebraska, Batesland Forma- Nebraska (Fig. 12C). The taxon was distinguished from S. scotti (which tion, South Dakota, Martin Canyon Formation (Clay Quarry), Colo- also occurs in Thomson Quarry) only by its smaller size and slender rado, and Oakville Formation, Texas; middle Hemingfordian Box Butte horns. As Skinner et al. (1977, p. 344-345) pointed out, these differences Formation, Nebraska, and Split Rock Formation, Wyoming. might just be due to the fact that the type specimen of S. wilsoni is a smaller and possibly less mature individual, and falls within the range of Barbouromeryx trigonocorneus (Barbour and Schultz, 1934) variation of S. scotti. Our own measurements (Fig. 10) place the type Figures 13-15; Table 1 specimen of S. wilsoni at the small end of the range of S. scotti, but the coefficients of variation (Table 1) are within the range for a single species, Dromomeryx trigonocorneus Barbour and Schultz, 1934 so we follow Skinner et al. (1977) in regarding S. wilsoni as a junior Barbouromeryx (Barbouromeryx) trigonocorneus Frick, 1937 synonym of S. scotti (which we regard as a junior synonym of S. Barbouromeryx (Probarbouromeryx) sweeti Frick, 1937 antilopinus). Barbouromeryx (Protobarbouromeryx) marslandensis Frick, 1937 Cranioceras kinseyi was named by Frick (1937, p. 91), based on Blastomeryx (Parablastomeryx) galushi Frick, 1937 a fragmentary right ramus with p2-m3 from the Kinsey Collection (num- Type specimen—UNSM 3-27-11-35, partial skull and rami (Fig. ber 3-6-1927), obtained from the early Barstovian lower Madison Valley 13A-E) with skeletal elements, “from 3.5 miles south, 9.5 miles west of beds in Montana. Frick (1937, p. 91) referred additional material from Hay Springs, Antelope Creek” (early Hemingfordian Runningwater For- the Deep River beds and from the north end of north Boulder Creek. mation, Nebraska). Although the type specimen is no longer available for study, a cast is Referred specimens—Nearly all the known material was listed present in the AMNH collections. It was referred to Rakomeryx kinseyi by Frick (1937, p. 134-136). by Tedford et al. (1987), and this was followed by Janis and Manning Diagnosis—Same as for genus (1998). However, close examination of the cast of the type specimen Description—Nearly all known material was described by Frick shows that it is much smaller than any known specimen of Rakomeryx (1937). (Fig. 10), and in size and morphology it is a much better match to S. Distribution—Same as for genus. antilopinus. We are not sure why Tedford et al. (1987) placed it in Discussion—Barbour and Schultz (1934, p. 2, 4) described a Rakomeryx, but since there is no diagnostic skull material known to be broken skull and rami (UNSM 3-27-11-33) as Dromomeryx associated with the type, we feel that it is a much better assigned to trigonocorneus, recognizing that it had the general appearance of Subdromomeryx antilopinus. The skull material mentioned by Frick is Dromomeryx, but that it was distinct (Fig. 13A) in having two short not clearly associated with the type specimen, but comes from a differ- horns over the orbits and a pronounced occipital knob (a precursor of the ent locality, so we cannot use this as evidence for its affinities with much longer occipital horn in later taxa). In addition to the distinctive Rakomeryx. horns, a large canine tusk was found with the skull (although the nasal and premaxillary regions are missing from the type). Tribe Cranioceratini Frick, 1937 Frick (1937, p. 134) made this specimen (and additional referred Characteristics—Males with supraorbital horns that are shifted material) the basis for his new genus and subgenus, Barbouromeryx anteriorly (nearly vertical), short to tall, triangular to rounded in cross (Barbouromeryx). All of the material came from the early Hemingfordian section, and lacking a basal flange. Posterior occipital region elongated, Runningwater Formation of Nebraska, primarily from the Antelope Creek with pronounced posterior dorsal projection of the occiput, producing a area in Dawes County (Janis and Manning, 1998, p. 484). Frick (1937) medial occipital horn of varying lengths. Lower rim of orbit expanded provided no diagnosis of his new genus Barbouromeryx or the species laterally. Absence of lacrimal vacuity but presence of a narrow, slit-like trigonocorneus, even though a much larger number of specimens was antorbital vacuity paralleling the anterior wing of the frontal. Upper available to him. canines present in Barbouromeryx only. Diastema moderate to long. Frick (1937, p. 135) named another new subgenus and species, Premolars variably reduced; posterior premolars unmolarized to Barbouromeryx (Probarbouromeryx) sweeti, based on UNSM 53-25-6- submolariform; anterior fossette (trigonid) on p4 may be open or closed; 35, a partial skull from Quarry 1 in the early Hemingfordian Runningwater dp1 lost in more derived taxa. Molars brachyodont to mesodont; Formation, near Bridgeport, Morrill County, Nebraska. His only diagno- Palaeomeryx fold present in lower molars of early taxa, but absent in sis claimed that the molars were smaller than B. (B.) trigonocorneus, but later ones. Limbs generally shorter and more heavily proportioned than larger than those of the blastomerycine Parablastomeryx gregorii. Fi- in the Dromomerycini; lateral digits may be present (after Janis and nally, Frick (1937, p. 136) erected the new subgenus and species Manning, 1998, p. 484). Barbouromeryx (Protobarbouromeryx) marslandensis, based on UNSM 3-24-7-34, a left ramus with p2 alveolus and p3-m3, from the Box Butte Barbouromeryx Frick, 1937 Formation “11 miles southwest of Marsland,” Dawes County, Nebraska. Blastomeryx Cook, 1934 (in part) His only diagnosis for this new subgenus and species was that the Barbouromeryx (Barbouromeryx) Frick, 1937 premolars were smaller proportioned, but that the molars approached Barbouromeryx (Probarbouromeryx) Frick, 1937 the size of B. (P.) sweeti. Barbouromeryx (Protobarbouromeryx) Frick, 1937 Thus, Frick (1937) created three monotypic subgenera of Blastomeryx (Parablastomeryx) Frick, 1937 (in part) Barbouromeryx, but the only apparent distinction between the taxa was size and relatively smaller premolars. Janis and Manning (1998, p. 484) Type and only species—B. trigonocorneus (Barbour and Schultz, noted that they in fact all appear to be about the same size, and that “the 1934) distinctness of the species may also be in question,” and this is borne out Diagnosis—Short upright supraorbital horns with bulbous tips. by our measurements (Fig. 14). Even though the sample is small, the size Occipital horn consisting of a short, median bulbous projection. Lacrimal range of trigonocorneus, sweeti, and marslandensis completely overlap, fossa present. Short diastema. Moderate-sized saberlike upper canines and the coefficients of variation of this sample (Table 1) are consistent in males. Large premolars with little molarization; anterior fossette on p4 with the hypothesis that this is a single species. Contrary to Frick open. brachyodont molars. Palaeomeryx fold present on lower molars. (1937), the specimens assigned to marslandensis range from shorter to Limbs moderately elongated (modified from Janis and Manning, 1998, p. longer premolar rows. It is a mystery why Frick did not measure more of 484). the specimens available to him, nor do any kind of simple plot to check 287

FIGURE 13. Barbouromeryx trigonocorneus. A-C, Type skull (UNSM 3-27-11-33) in dorsal, lateral, palatal views; D-E, Type jaws in occlusal and lateral views. Scale bar in cm. whether his subjective impressions of size were in fact supported by the (notes found in specimen drawer). Thus, we synonymize Blastomeryx data, but it is clear that there is no basis for distinguishing these three (Parablastomeryx) galushi with Barbouromeryx trigonocorneus (Barbour taxa. It seems likely that Frick was splitting them based on locality, even and Schultz, 1934). though they are all from the same formation in a relatively small area of Specimens possibly referable to Barbouromeryx trigono- western Nebraska. Thus, they are all here considered synonyms, and corneus—Cook (1934, p. 158) named the new species Blastomeryx cur- trigonocorneus is the senior trivial name. In agreement with Janis and sor, based on a fragmentary ramus (Fig. 15B) with p2-m3 (Harold Cook Manning (1998, p. 484), we also regard the subgenera as useless, since collection 142, now AMNH 81086) from the “upper Harrison” beds they were never properly diagnosed, have no basis in fact, and are super- (now Anderson Ranch Formation of Hunt, 2002) four miles northeast of fluous when each is monotypic. Thus, the only valid arrangement is a Agate, Nebraska. The fragmentary material was difficult to assess at the single genus and species, Barbouromeryx trigonocorneus (Barbour and time, although Cook (1934) compared it to Leptomeryx and “Blastomeryx Schultz, 1934). riparius” (now Sinclairomeryx riparius) and the living brocket deer Frick (1937, p. 244) erected the species Blastomeryx Mazama. Frick (1937) made no mention of this species, even though he (Parablastomeryx) galushi based on a crushed skull (F:AM 33775) from had large collections from the same area. During curation of the Frick the “Upper Marsland” Formation in the Hay Springs area, Dawes County, Collection, Beryl Taylor observed that the m3 of the type of Blastomeryx Nebraska. He compared it only to the blastomerycine specimens in his cursor is a good match for Barbouromeryx trigonocorneus. This syn- collection, but it is clearly too large for any blastomerycine. Instead, it an onymy was suggested by Janis and Manning (1998, p. 484), based on excellent match for the type skull of Barbouromeryx trigonocorneus Taylor’s observations, although they did not formalize it. Nor do we (Fig. 15A), as noted by Beryl Taylor when he curated the collection formalize that synonymy here, because the type material of Blastomeryx 288

FIGURE 14. Bivariate plot of m1-3 length vs. p2-4 length of specimens of Barbouromeryx and Bouromeryx. Solid diamonds = B. trigonocorneus; open squares = B. sweeti; open triangles = B. marslandensis; open circles = B. americanus; solid circles = B. submilleri. Abbreviations of type specimens: Am = B. americanus; Mil = B. milleri; Neb = B. nebrascensis; Parv = B. parvus; Paw = B. pawniensis; Psu = B. pseudonebrascensis; Sub = B. submilleri; Sup = B. supernebrascensis. cursor is so poor and non-diagnostic. Blastomeryx cursor is best re- garded as a nomen dubium. Blastomeryx vigoratus was named by Hay (1924) based on an isolated m2-3 (TAM 2378) and paratypes (under the same number) consisting of a right M3 and left m1 (Fig. 15C). These isolated teeth were discovered in the early Hemingfordian Garvin Gully l.f., Oakville Forma- tion, Grimes County, Texas. Frick (1937) referred the material question- ably to Longirostromeryx. Patton (1969) considered the type specimens to be too fragmentary to assign to any known taxon, so it would be a nomen dubium. Webb (1998, p. 472) considered it to be referable to Blastomeryx, since other Garvin Gully material lacks the long diastema of Longirostromeryx. We agree with Patton (1969) that the specimens are too poor to be diagnostic. However, Beryl Taylor (notes in AMNH collection, 1974) made detailed comparisons, and thought that the type material could be assigned to Barbouromeryx trigonocorneus, although again it is best to regard the name as a nomen dubium. Bouromeryx (Frick, 1937) Palaeomeryx Douglass, 1899 (in part) Dromomeryx Douglass, 1909 (in part) Dromomeryx Cook, 1922 (in part) Blastomeryx Cook, 1922 (in part) Blastomeryx Cook, 1934 (in part) Barbouromeryx (Bouromeryx) Frick, 1937 Rakomeryx Shotwell, 1968 FIGURE 15. Comparison of the type specimens of questionable taxa with Bouromeryx Webb, 1983 the type of Barbouromeryx trigonocorneus. (UNSM 3-27-11-33). A, Bouromeryx Tedford et al., 1987 Comparison with “Parablastomeryx marshi” (F:AM 33775). B, Comparison Bouromeryx Voorhies, 1990 with “Blastomeryx cursor” (AMNH 81086). C, Comparison with Bouromeryx Janis and Manning, 1998 “Blastomeryx vigoratus” (TAM 2378). Scale bar in cm. Type species—B. americanus (Douglass, 1909) California, Nebraska and Saskatchewan; early Barstovian of Montana, Included species—B. submilleri Frick, 1937 Nevada, Oregon, California, Colorado, Nebraska, Florida, and Texas; late Diagnosis—Medium-length, upright supraorbital horns, short Barstovian of Nebraska, Montana, and Texas. bulbous occipital horn. Upper canine lost. Short diastema. Large premolars Discussion—Material of a medium-sized late Hemingfordian- with little molarization; anterior fossette on p4 open. brachyodont early Barstovian cranioceratin with medium-sized occipital and supraor- molars, with Palaeomeryx fold on lower molars (after Janis and Man- bital horns was first described by Douglass (1899) as Palaeomeryx ning, 1998, p. 485). americanus, and then in 1909 as Dromomeryx americanus. Frick (1937, Distribution—Late Hemingfordian of Montana, Oregon, Nevada, p. 131) had much more material available to him, and recognized that it 289 was not Dromomeryx, but related to Barbouroumeryx and Cranioceras, tell, the only criterion that distinguishes most of Frick’s (1937) species so he erected Bouromeryx as a subgenus without indicating to which of Bouromeryx is the quarry from whence they came. Two species, B. genus it was referred. Most authors have interpreted Frick’s (1937) supernebrascensis (Fig. 16C) and B. pseudonebrascensis (Fig. 16D) are intent to place it as a subgenus of Barbouroumeryx. As Webb (1983), even from the same locality in the early Barstovian Sand Canyon Forma- Tedford et al., (1987), Voorhies (1990, p. A221-A222) and Janis and tion in Dawes County (Observation Quarry), but Frick (1937) provides Manning (1998, p. 485) pointed out, however, Bouromeryx is a dis- no criterion for distinguishing them. B. nebrascensis (Fig. 16E) is like- tinctly larger and more derived taxon, and deserves its own genus, so wise undiagnosed, but based on specimens from Echo Quarry in the they raised the subgenus to generic rank. Olcott Formation of Sioux County, Nebraska. B. pawniensis (Fig. 16F) Bouromeryx is one of the most widespread dromomerycine gen- was apparently named a new species because it comes from the early era, found in nearly every important late Hemingfordian and Barstovian Barstovian part of the Pawnee Creek Formation of Colorado. B. milleri locality. However, it is still poorly known. Nearly all the material con- (Fig. 16G) and B. submilleri (Fig. 17) both come from the same late sists of lower jaws and rami, with only a few poor skulls and maxillae Hemingfordian Sheep Creek Formation, but different quarries (Greenside recorded so far, and few postcranials. Quarry and Draw, respectively). Although they were not diag- nosed, there is a clear size difference between them. Bouromeryx americanus (Douglass, 1899) Cook (1922, p. 21) described a partial left ramus with p4-m3 Figures 14, 16; Table 1 (AMNH 81018) from the Olcott Formation as Dromomeryx parvus (Fig. 16H). Frick (1937, p. 131) transferred this taxon to Bouromeryx Palaeomeryx americanus Douglass, 1899 without justification or diagnosis. Skinner et al. (1977, p. 349) pointed Palaeomeryx madisonius Douglass, 1899 out that B. parvus was indistinguishable from B. nebrascensis Frick, Dromomeryx americanus Douglass, 1909 1937, from the same area and the same beds, and so synonymized B. Dromomeryx madisonius Douglass, 1909 nebrascensis with B. parvus. Voorhies (1990, p. A224) noted that both Blastomeryx parvus Cook, 1922 B. parvus and B. nebrascensis were very similar to Douglass’ (1909) B. Bouromeryx milleri Frick, 1937 americanus, and suggested they were all synonyms of Douglass’ taxon. Bouromeryx nebrascensis Frick, 1937 However, he did not deal with the rest of Frick’s (1937) oversplit and Bouromeryx supernebrascensis Frick, 1937 undiagnosed species of Bouromeryx. Bouromeryx pseudonebrascensis Frick, 1937 Because nearly all of these late Hemingfordian-early Barstovian Bouromeryx pawniensis Frick, 1937 species of Bouromeryx were based on lower jaws, with no apparent Dromomeryx americanus McGrew, 1938 distinctions other than size, we measured the entire Frick sample of Rakomeryx americanus Shotwell, 1968 these species (Fig. 14). All of the bivariate plots of different variables Type specimen—CMNH 705, left ramus p2-m3, from the Madi- show only two distinct and diagnosable size clusters: a smaller one (for son River beds, Montana (Fig. 16A). which the only available name is B. submilleri Frick, 1937) and a larger Referred specimens—Nearly all the known specimens were listed one (for which the first available name is B. americanus Douglass, 1909). by Frick (1937, p. 130-134). These clusters are statistically distinct, with a t-test probability of p<0.5. Diagnosis—Larger species of Bouromeryx (Table 1). Both samples have univariate binomial distributions (Kologmorov-Smirnov Distribution—Late Hemingfordian: Box Butte and Sheep Creek test, p<0.05). Because Frick provided no diagnoses and there are no formations, Nebraska; Massacre Lake l.f., Nevada; Topham l.f., Cypress morphological features to distinguish them, most of his names are tech- Hills, Saskatchewan; Early Barstovian: Madison Valley and Fort Logan nically nomina nuda. However, it is simplest to regard B. nebrascensis, formations, Montana; Olcott Formation, Sand Canyon Formation, and B. pseudonebrascensis, B. supernebrascensis, B. milleri, and B. pawniensis equivalents, Nebraska; Round Mountain Silt, Sharktooth Hill bone bed, (all named by Frick, 1937) as well as the older taxa B. madisonius and B. California; Crowder Formation, California; Torreya Formation, parvus as junior synonyms of Bouromeryx americanus (Douglass, 1909). Willacoochee Creek l.f., Florida; Lower Bone Valley Formation, Florida; Clustering of these taxa within B. americanus is biologically defensible, Trinity River l.f., Texas; Pawnee Creek Formation, Colorado; Late because the coefficients of variation of most dental variables (Table 1) are Barstovian: Cornell Dam Member, Valentine Formation, Nebraska within the range for a biological species. Instead of nine species of (Voorhies, 1990); Cold Spring l.f., Texas; Barnes Creek beds, Flint Creek Bouromeryx in the late Hemingfordian and early Barstovian of the Great l.f., Montana (after Janis and Manning, 1998, p. 485). Plains and Montana, we believe that there are only two valid species (the Description—Douglass (1909) and Frick (1937) described most smaller B. submilleri and the larger B. americanus, formerly B. milleri) of the known material of Bouromeryx americanus. from the late Hemingfordian, and only one (B. americanus) out of the Discussion—Douglass (1899, p. 20) first described CMNH 705, original eight named species from the early Barstovian. a left ramus with p2-m3 (Fig. 16A) from the early Barstovian Deep Bouromeryx submilleri Frick, 1937 River beds (Fort Logan Formation), Montana, as Palaeomeryx Figures 14, 17; Table 1 americanus. In 1909, he transferred this taxon to Dromomeryx americanus, recognizing that it was similar to his newly named Dromomeryx borealis Type specimen—F:AM 33729, right ramus with p2-m3 (Fig. skeleton, but smaller. In the same papers, he also described a broken 17), from Greenside Quarry, Sheep Creek Formation, Nebraska. ramus (Fig. 16B) with broken m1-3 (CMNH 755) from the same beds, Referred specimens—Frick (1937, p. 131) listed only the type originally as Palaeomeryx madisonius, then, in 1909, as Dromomeryx specimen (F:AM 33729). In addition, the following specimens are among madisonius. The only distinction was that the teeth were supposedly the referred material in the Frick Collection from the late Hemingfordian more slender, and the unworn teeth slightly more hypsodont, although Sheep Creek Formation: F:AM 53040, 53037, 53038. they are the same size and are otherwise identical. Diagnosis—Smaller species of Bouromeryx (Table 1). Based on much larger collections with better material, Frick (1937) Distribution—Late Hemingfordian Box Butte and Sheep Creek assigned both of these species to his new subgenus Bouromeryx. As Formations, Nebraska; Olcese Sand, California; Massacre Lake l.f., Ne- Voorhies (1990, p. A221) and Janis and Manning (1998, p. 485) pointed vada; Haystack Valley Member, John Day Formation, Oregon (fide Janis out, he grossly oversplit the genus, recognizing nine different species. In and Manning, 1998, p. 485). addition to the three already referred to the genus, Frick (1937) named six Description—The known material of B. submilleri was described additional new species based on jaws from different quarries in Nebraska by Frick (1937, p. 131), and no new material has been reported since and Colorado, without any comparisons or diagnoses. So far as we can then. 290

FIGURE 16. Bouromeryx americanus. A, CMNH 705, type of B. americanus (after Douglass, 1909, plate LXII, figs. 1-2). B, CMNH 755, type of B. madisonius (after Douglass, 1909, plate LXII, figs. 5-6). C, F:AM 33733, type specimen of B. supernebrascensis. D, F:AM 33735, type specimen of B. pseudonebrascensis. E, F:AM 31193, partial skull and type ramus of B. nebrascensis. F, F:AM 31290, type specimen of B. pawniensis. G, AMNH 21533, type specimen of B. milleri. H, AMNH 81018, type specimen of B. parvus. Scale bar in cm. 291

FIGURE 18. Procranioceras skinneri, F:AM 31250, type skull (after Frick, 1937, Fig. 11, p. 74).

from Cranioceras. They also observed that placing Procranioceras within Cranioceras makes the latter genus paraphyletic, so we follow Janis and Manning (1998) and a number of other recent workers in treating it as a distinct genus. Procranioceras skinneri (Frick, 1937) Cranioceras (Procranioceras) skinneri Frick, 1937 Type specimen—F:AM 31250, skull and ramus, from the latest Barstovian Devil’s Gulch Horse Quarry, Devil’s Gulch Member, Valen- tine Formation (Fig. 18). Referred specimens—Most of the known material was listed by Frick (1937, p. 86-88). Diagnosis—Same as for genus. Distribution—Same as for genus. Description—No additional material has been reported since Frick (1937), so no further description is warranted here. Discussion—Unlike nearly every other Frick dromomerycine taxon, Procranioceras was erected with only one species, P. skinneri (based on an outstanding skull that has been illustrated many times), so it is not oversplit. It is easily distinguished from Bouromeryx by its FIGURE 17. Bouromeryx submilleri, F:AM 33729, type specimen, in occlusal larger size and longer supraorbital and occipital horns, and from all spe- and lateral views. Scale bar in cm. cies of Cranioceras by its shorter and more anteriorly curved occipital horn. Janis and Manning (1998, p. 485) point out that its first appear- Discussion—As noted above, of the nine species of Bouromeryx ance in the late Barstovian is actually later than the first appearance of its originally recognized by Frick (1937), only the late Hemingfordian spe- descendant species, Cranioceras, in the early Barstovian. Thus, there is cies B. submilleri stands out as distinctly smaller and worthy of recogni- not a strict chronocline of taxa within the cranioceratins (contrary to tion (Fig. 14). Webb, 1983, fig. 1). Procranioceras Frick, 1937 Cranioceras Matthew, 1918 Figure 18; Table 1 Cosoryx Cope, 1874 (in part) Cranioceras (Procranioceras) Frick, 1937 Dicrocerus Cope, 1875 (in part) Procranioceras Janis and Manning, 1998 Palaeomeryx Gidley, 1907 (in part) Cranioceras Matthew, 1918 Type and only species—Procranioceras skinneri (Frick, 1937) Cranioceras Frick, 1937 Diagnosis—Differs from Cranioceras in having a shorter occipi- tal horn, which is transversely flattened and anteriorly curved. Both the Type species—Cranioceras unicornis Matthew, 1918 occipital and supraorbital horns are much longer than those of Included species—Cranioceras teres (Cope, 1874) Bouromeryx. The premolars are larger than those in Cranioceras, but the Diagnosis—Long, upright supraorbital horns, tapering distally anterior fossette on p4 tends to be open. Molars more brachyodont, and curved slightly inward; round in midshaft cross-section; long median usually with the Palaeomeryx fold (modified from Janis and Manning, occipital horn, round in cross-section and directed posteriorly. No upper 1998, p. 485). canine. Short to moderate-length diastema. Premolar row shortened; an- Distribution—Late Barstovian, Crookston Bridge and Devil’s terior fossette on p4 open. Brachyodont to mesodont molars with Gulch members, Valentine Formation, Nebraska; Wood Mountain For- Palaeomeryx fold usually lost (modified from Janis and Manning, 1998, mation, Saskatchewan. p. 485). Discussion— Frick (1937) originally erected Procranioceras as Distribution—Early Barstovian, California, New Mexico, Ne- a subgenus of Cranioceras. As Janis and Manning (1998, p. 485) point braska; late Barstovian, Nebraska, New Mexico; early Clarendonian, out, however, it is a very distinct taxon, worthy of generic separation California, New Mexico, Texas, South Dakota, Nebraska; late 292 Clarendonian, California, Nebraska. beds of Colorado, it was designated a new taxon. Discussion— Cope (1874) first recognized the existence of a As noted by Janis and Manning (1998, p. 486), the supposed late taxon with unusual horns when he described a partial occipital horn he Barstovian first occurrence of Cranioceras (Tedford et al., 1987) has called Cosoryx teres from the early Clarendonian of the Chamita Forma- now been questioned by the possibility of a new unnamed species of tion of New Mexico. Originally assigning it to the pronghorn genus Cranioceras from the late Hemingfordian and early Barstovian of the Cosoryx, in 1875 he transferred the material to the cervid genus Dicrocerus. Caliente Formation in California (Kelly and Lander, 1988), as well as In 1907, Gidley transferred it to the genus Palaeomeryx, but little else possible early Barstovian records of C. unicornis in Nebraska (Survey was written about the specimen until Frick (1937) assigned it to Quarry, Sand Canyon beds) and early Barstovian records of C. teres in Cranioceras, a genus based on another unusual horn described by Mat- the Skull Ridge Member of the Tesuque Formation of New Mexico. As thew in 1918. noted above, the derived taxon Cranioceras appears earlier in many Frick (1937) considerably expanded the scope of Cranioceras places (early Barstovian of California, New Mexico, and Nebraska) than beyond Cope’s and Matthew’s original two species. He named its supposed primitive ancestor, the late Barstovian Procranioceras. Cranioceras granti and Cranioceras mefferdi from the early Clarendonian lower Ash Hollow Formation and late Barstovian Valentine Formation of Cranioceras unicornis Matthew, 1918 Nebraska (respectively), Cranioceras dakotensis from the “vicinity of Figures 19-20; Table 1 the Rosebud Agency, South Dakota,” Cranioceras pawniensis from the Cranioceras unicornis Matthew, 1918 Clarendonian of the Pawnee Creek area, Colorado, and Cranioceras Cranioceras granti Frick, 1937 clarendonensis from the early Clarendonian MacAdams Quarry, near Cranioceras mefferdi Frick, 1937 Clarendon, Texas. Most of these taxa were based on large samples of mandibles and rami, although some had associated skull material that Type specimen—AMNH 17343, fragmentary occipital horn, from showed the distinctive long vertical supraorbital horns and posteriorly- the late Clarendonian Laucomer Member of the Snake Creek Formation, inclined occipital appendage. Thus, with his large sample Frick (1937) Sinclair Draw, Sioux County, Nebraska (Fig. 20A-B). was able to reconstruct most of the cranial anatomy of the genus Referred specimens—Most of the known material was listed Cranioceras, but as usual, he oversplit it into numerous similar species by Frick (1937, p. 82-97). without adequate diagnoses, largely based on their different provenance. Diagnosis—Larger species of Cranioceras (Table 1). Webb (1969), in his review of the Burge sample of Cranioceras in Distribution—Early Barstovian Sand Canyon beds, Dawes the UCMP, synonymized many of Frick’s (1937) invalid taxa. He placed County, Nebraska; late Barstovian Devil’s Gulch and Burge members, C. granti, C. mefferdi, C. dakotensis and McGrew’s (1938) Dromomeryx Valentine Formation, Nebraska; late Clarendonian Laucomer Member parvus in synonymy with C. unicornis. Janis and Manning (1998, p. and early Hemphillian Johnson Member, Snake Creek Formation, Ne- 485-486) summarized the named species of Cranioceras but did not braska; early Clarendonian Cap Rock Member and late Clarendonian synonymize them further. Merritt Dam Member, Ash Hollow Formation, Nebraska; late In examining Frick’s (1937) taxa and measuring the Cranioceras Clarendonian North Tejon Hills l.f., Chanac Formation, California. specimens in the Frick Collection, it became apparent that there are few Description—Almost all of the known material of C. unicornis differences in the various named species except size and provenance. was described by Frick (1937). Thus, we measured and plotted numerous variables of the lower denti- Discussion— Matthew (1918, p. 223) described a fragmentary tion and diastema, and found only two clusters that are distinct (Fig. 19). horn (AMNH 17343) from the late Clarendonian Laucomer Member of There is a larger cluster that is assignable to C. unicornis Matthew, 1918, the Snake Creek Formation (Skinner et al., 1977) of Nebraska (Fig. 20A- and includes C. granti Frick, 1937, and C. mefferdi Frick, 1937. There is B) as Cranioceras unicornis. It seemed to suggest an with a single also a smaller cluster whose senior name would be C. teres (Cope, 1874), occipital horn, reminiscent of a unicorn. Matthew (1918) also referred a and includes C. clarendonensis Frick, 1937, and C. dakotensis Frick, ramus (AMNH 17344) to this taxon, but Frick (1937, p. 82) argued that 1937. These two clusters are statistically distinct, with a student’s t-test they do not belong together, and made the ramus the type specimen of probability of p<0.5, and both samples have univariate binomial distri- butions (Kologmorov-Smirnov test, p<0.05). In addition, the coeffi- cients of variation of the two clusters (Table 1) are reasonable for a single species, but if the entire sample of Cranioceras is lumped together, the CV’s are greater than 10, too large for a single species. Thus, we recog- nize only two of Frick’s (1937) original seven species. Cranioceras pawniensis Frick (1937, p. 93) was based on a frag- mentary supraorbital horn (F:AM 31294) from the early Clarendonian of the Pawnee Buttes area, Colorado. There were no additional speci- mens referred to this species, so it is not possible to compare its dental dimensions to the other better-characterized taxa. Frick (1937, p. 93) compared it to a specimen of Procranioceras skinneri (F:AM 31264) from the Devil’s Gulch area of the Valentine Formation. However, it could also match some of the specimens referred to Cranioceras. As Frick (1937) noted, it is shorter and more attenuated than other known specimens of the supraorbital horn, but this may be because it represents a juvenile. Given the variability of horns in many groups of ruminants, and the fact that this specimen bears marks of juvenile, it is unlikely that the “diagnostic” features that Frick (1937) used to erect the species C. pawniensis can be justified. Instead, we consider the single type speci- men inadequate to diagnose a species, and consider C. pawniensis a FIGURE 19. Bivariate plot of m1-3 length vs. p2-4 length of lower jaws of nomen dubium. If the specimen had come from the better-sampled locali- Cranioceras. Open circles = C. granti; solid circles = topotypic samples of ties in Nebraska, we suspect that Frick would not have given it a new C. unicornis; open squares = C. dakotensis; solid diamonds = C. name. Because it was the only cranioceratine from the Pawnee Creek clarendonensis; open triangles = topotypic material of C. teres. 293 the protoceratid Prosynthetoceras siouxensis. Frick (1937, p. 83-84) referred additional specimens from the early Barstovian Olcott Forma- tion to C. unicornis, and on this basis Webb (1969, p. 168) synonymized several of the species of Cranioceras. Skinner et al. (1977, p. 349) clarified the confused stratigraphy and locality information of the Sheep Creek-Olcott-Snake Creek beds. They checked the locality information carefully, and argued that there are no Cranioceras in the Olcott Forma- tion, and that much of Frick’s (1937) alleged topotypic sample is actu- ally Rakomeryx. Accordingly, the only material in Frick’s (1937) sample that actually comes from the same formation as the type (Laucomer Member of the Snake Creek Formation) are derived from just two Frick quarries, Olcott Quarry and “The Pits.” This considerably reduces the known topotypic sample of Cranioceras unicornis. Frick (1937, p. 84) named another species, C. granti, based on F:AM 32064, a broken cranium that clearly shows the long supraorbital horns and posteriorly-inclined occipital horn (Fig. 20C). It differs little from the material referred to C. unicornis, except that the former comes from the early Clarendonian Leptarctus Quarry, in the Merritt Dam Member of the Ash Hollow Formation (Skinner and Johnson, 1984, p. 316), and the latter from the Snake Creek Formation. Frick (1937, p. 77) himself noted that C. granti does not differ in size or cranial characters from C. unicornis, and they are distinct only in their provenance, and on this basis Webb (1998, p. 169) synonymized the two. As can be seen from Figure 19, the type of C. unicornis falls with the large cluster of Valentine specimens referred to C. granti, so this synonymy is reason- able. Frick (1937, p. 88) described C. mefferdi based on F:AM 32243, a fragmentary skull that shows the same Cranioceras condition of the horns (Fig. 20D). He provided no diagnosis for this species, and it differs from C. unicornis and C. granti only in that it is derived from near Nenzel Quarry in the late Barstovian Burge Member of the Valentine Formation (Skinner and Johnson, 1984, p. 293). Webb (1969, p. 169) noted that C. mefferdi is identical in size to C. unicornis, and differs only in that it comes from a different locality, and we support this synonymy. Cranioceras teres (Cope, 1874) Figures 19, 21; Table 1 Cosoryx teres Cope, 1874 Dicrocerus teres Cope, 1875 Palaeomeryx teres Gidley, 1907 Cranioceras teres Frick, 1937 Cranioceras clarendonensis Frick, 1937 Cranioceras dakotensis Frick, 1937 Type specimen—USNM 2044, fragment of cranium with broken horns (Fig. 21A), from the “Santa Fe marls” (early Clarendonian Chamita Formation of New Mexico, fide Galusha and Blick, 1975). Referred specimens— Most of the known material was listed by Frick (1937, p. 82-97). Diagnosis—Smaller species of Cranioceras (Table 1). Distribution—Early Barstovian Skull Ridge Member and late Barstovian Chama-el-Rito Member, Tesuque Formation, New Mexico; early Clarendonian Chamita and Pojoaque formations, New Mexico; early Clarendonian Clarendon beds, Texas; early Clarendonian Lapara Creek Member, , Texas; early Clarendonian Merritt Reservoir Member, Ash Hollow Formation, South Dakota; early Clarendonian South Tejon Hills l.f., California. Description—Almost all of the known material was described by Frick (1937). Discussion—As discussed above, Cope (1874, p. 150) first de- scribed the fragmentary cranium with a partial occipital horn (USNM 2044) as Cosoryx teres (as an antilocaprid), then in 1875 transferred it to the cervid Dicrocerus. Gidley (1907) referred it to the genus Palaeomeryx. FIGURE 20. Cranioceras unicornis. A-B, AMNH 17343, type specimen in Frick (1937, p. 92-93) transferred P. teres to Matthew’s (1918) genus anterior and lateral views. C, F:AM 32064, type skull of C. granti in lateral Cranioceras, and referred a number of additional specimens from the view. D, F:AM 32243, type skull of C. mefferdi. Scale bars in cm. 294

FIGURE 21. Cranioceras teres. A, USNM 2044, type specimen in lateral view. B, F:AM 32454, type specimen of C. clarendonensis. C, AMNH 10952, type specimen of C. dakotensis. D, F:AM 52781, referred skull of C. dakotensis (= C. teres). Scale bar in cm. Chamita Formation to this taxon. These specimens (Fig. 19) plot in the premolars. He made no comparisons to the many other species of smaller size cluster, so this makes Cranioceras teres the senior name for Cranioceras, however. Webb (1969) suggested that is was a junior syn- all the smaller species of Cranioceras. onym of C. unicornis, but provided no detailed analysis of the material. Frick (1937, p. 94) described another new species, C. Measurements of the referred rami in the Frick Collection (Fig. 19) show clarendonensis, based on a large sample from the early Clarendonian that most of the specimens referred to C. dakotensis falls within the (primarily MacAdams Quarry) of Texas. He designated F:AM 32454, a smaller size cluster, and is a junior synonym of C. teres, not C. unicornis. right ramus with p2-m3 (Fig. 21B) as the type specimen, and referred and illustrated a few broken horns and dozens of rami to this taxon. Yumaceras (Frick, 1937) However, he provided no adequate diagnosis to distinguish it from other Yumaceras Frick, 1937 smaller Cranioceras, and we can find no characteristics that distinguish Pediomeryx Savage, 1951 it from the New Mexico sample of C. teres. Indeed, the entire sample Pediomeryx (Yumaceras) Webb, 1983 (Fig. 19) encompasses the range of variation of C. teres, so there are good Pediomeryx (Yumaceras) Janis and Manning, 1998 grounds for considering C. clarendonensis a junior synonym of C. teres. Frick (1937, p. 90) named another new species, C. dakotensis, Type species—Yumaceras figginsi (Frick, 1937) based on AMNH 10952, a right ramus with p2-m3 (Fig. 21C) “from the Included species—Yumaceras hamiltoni Webb, 1983; Y. ruminalis vicinity of the Rosebud Agency, South Dakota.” He suggested that it Stirton, 1936 might be “Lower Miocene” (Arikareean) in age. Webb (1969, p. 169) cast Diagnosis—Long, nearly vertical supraorbital horns with doubt on this provenance, and Skinner and Johnson (1984, p. 320) showed retrocurved and anteriorly flattened tips, and round midshaft section. that this specimen actually came from the early Clarendonian Ash Hol- Occipital appendage longer than in Cranioceras, and rising more verti- low Formation. Additional referred material included a number of AMNH cally, with more anteroposteriorly flattened tip. No upper canine. Di- specimens from the same locality, as well as partial skulls (Fig. 21D). astema moderate. Mandible with nearly straight ventral border. Premolar Frick (1937, p. 90) provided no diagnosis of his species other than to row reduced, with p2 greatly reduced; p4 closed lingually by long meta- note that it was smaller than Procranioceras skinneri, but had shorter conid. Mesodont molars without Palaeomeryx fold (modified from Janis 295 and Manning, 1998, p. 486). of taste (and avoiding paraphyly). We have already discussed our rea- Distribution—Latest Clarendonian Love Bone bed and early sons for rejecting subgenera in the dromomerycines and aletomerycines , Hemphillian Mixson’s bone bed, , Florida; early so it makes more sense to keep Yumaceras and Pediomeryx as separate Hemphillian Norris Canyon l.f., Siesta Formation, California; middle genera. Although they are similar in many ways, Yumaceras is part of the Hemphillian Kern River Formation, California; late Clarendonian to middle increasing size trend through the late Clarendonian to middle Hemphillian, Hemphillian, Ogallala Formation, Texas; middle Hemphillian Wray l.f., while Pediomeryx hemphillensis is the late Hemphillian species that Ogallala Formation, Colorado; middle Hemphillian Johnson Member, gradually reduced in size through time. There is no need to review the Snake Creek Formation, Nebraska; early Hemphillian Ash Hollow For- species-level taxonomy of Pediomeryx hemphillensis, because it was mation, Nebraska and Oklahoma; early Hemphilian Drewsey Forma- updated by Webb (1983) and by Janis and Manning (1998). tion, Oregon. Discussion—Yumaceras figginsi was named by Frick (1937, 143) TEMPORAL, DIVERSITY, AND BIOGEOGRAPHIC PATTERNS based on a skull (DMNH 314) from the middle Hemphillian Wray locali- ties, Yuma County, Colorado. It was based on very incomplete material, Once the confusion of Frick’s (1937) taxonomy is cleared away, with large cheek teeth showing highly reduced premolars, but little cra- an interesting pattern of temporal distribution of the 17 valid nial material. Frick (1937) placed Yumaceras with the Aletomerycini dromomerycine species emerges (Figure 22). It differs markedly with the because of its dental characteristics. Just months earlier, Stirton (1936) simplistic orthogenetic cranioceratin lineage shown by Webb (1983, fig. named Pediomeryx hemphillensis, based on material (UCMP 30703) 1), or with the generic range distribution (they did not attempt to plot the from the late Hemphillian Coffee Ranch Quarry (= UCMP Miami Quarry) many invalid species of Frick, 1937) shown by Janis and Manning (1998, of Texas. Stirton (1944) suggested that the two genera might be syn- fig. 32.4). In contrast to earlier interpretations that had at least three onyms. The confusion was not resolved until Webb (1983) described subgenera and five species in the late Arikareean, only one species, additional new material from Love Bone Bed in Florida that showed that Barbouromeryx trigonocorneus (and possibly two, if Aletomeryx graci- Yumaceras and Pediomeryx had occipital horns that placed them with lis is truly known from the late Arikareean) is known during that time. As the Cranioceratini, not the Aletomerycini. Webb (1983) suggested that mentioned by Janis and Manning (1998), the distribution of the Yumaceras should be treated as a subgenus of Pediomeryx, and this was aletomerycin-dromomerycin and cranioceratin lineages in time suggests followed by Janis and Manning (1998, p. 486). However, these authors that there were at least two different immigration events from Eurasia, also pointed out that the two subgenera were quite distinctive, and could one of which brought the cranioceratins about 20 Ma and the other of easily be restored to generic rank. Given that most of the subgenera which brought the more primitive aletomerycins and dromomerycins within the dromomerycines have proven superfluous, we agree that it is about 18 Ma (or possibly earlier). When they first appear, dromomerycines simpler to restore Yumaceras to generic rank, and clarify and simplify are widespread over the entire earliest Miocene outcrop in North America. the taxonomy, especially since placing it within Pediomeryx makes that Barbouromeryx trigonocorneus is known not only from the High Plains genus paraphyletic. of Nebraska, South Dakota, and Colorado, but also from central Wyo- Webb (1983) and Janis and Manning (1998) updated the species- ming and the Texas Gulf Coastal Plain. Aletomeryx occurs in Nebraska level taxonomy of these genera, so there is no need to review the species and Colorado, but also in the Mojave Desert of California. here. Yumaceras was the common latest Clarendonian-early Hemphillian By the late Hemingfordian, Aletomeryx was gone, replaced by dromomerycine, whose size increased gradually through this time until Sinclairomeryx riparius, plus the ghost lineage of Drepanomeryx the peak size was reached in the middle Hemphillian (Wray sample) with falciformis, and known occurrences of Rakomeryx sinclairi, Dromomeryx the appearance of Yumaceras figginsi. In the late Hemphillian, Pediomeryx borealis, Subdromomeryx antilopinus, Bouromeryx submilleri, species were characterized by decreasing body size (Webb, 1983, fig. 7). Bouromeryx americanus, and relict Barbouroumeryx trigonocorneus. This late Hemingfordian increase of 6 genera and 7 species (plus one Pediomeryx Stirton, 1936 additional ghost lineage) represents a dramatic development of dromomerycine diversity, as also shown by Janis (2000, fig. 3.5, based Pediomeryx Stirton, 1936 on older generic diversity data). At this point, the dromomerycines were Procoilus Frick, 1937 also biogeographically widespread. Sinclairomeryx riparius is known Yumaceras Frick, 1937 (in part) from Nebraska and Saskatchewan; Rakomeryx sinclairi from Nebraska, Pediomeryx (Pediomeryx) Webb, 1983 Montana, California, and Florida; Dromomeryx borealis from Nebraska Pediomeryx (Pediomeryx) Janis and Manning, 1998 and Montana; Subdromomeryx antilopinus from Nebraska, Montana, Type and only species—P. hemphillensis Stirton, 1936 (= and Nevada; Barbouromeryx trigonocorneus from Nebraska and Wyo- Procoilus edensis Frick, 1937; = Yumaceras falkenbachi Frick, 1937). ming; Bouromeryx submilleri from Nebraska, California, Nevada, and Diagnosis—Similar to Yumaceras but with more hypsodont cheek Oregon; and Bouromeryx americanus from Nebraska, Nevada, and teeth and smaller size (modified from Janis and Manning, 1998, p. 486). Saskatchewan. Distribution—Middle Hemphilllian, Alachua Formation, Florida; In the early Barstovian, diversity was at its peak. Sinclairomeryx late Hemphillian Mehrten Formation, California; latest Hemphilllian Mt. riparius, Drepanomeryx falciformis, Rakomeryx sinclairi, Dromomeryx Eden l.f., California; late Hemphillian Hemphill beds, Oklahoma and borealis, Subdromomeryx antilopinus, and Bouromeryx americanus per- Texas; late Hemphillian Johnson Member, Snake Creek Formation, Ne- sisted from the late Hemingfordian. Barbouromeryx trigonocorneus was braska; middle Hemphillian Cambridge l.f., Nebraska; latest Hemphillian gone, but Cranioceras unicornis and C. teres (plus the ghost lineage of Devil’s Nest Airstrip l.f., upper Ash Hollow Formation, Nebraska. Procranioceras skinneri) are added. This diversity of 7 genera and 8 Discussion—As discussed above, Pediomeryx was named by species (plus another ghost lineage) is the highest in the history of the Stirton in 1936, based on some of the same material that Frick (1937) group, and higher than that shown by Janis (2000, fig. 3.5). These spe- assigned to Yumaceras. Stirton (1944) placed Yumaceras in synonymy cies are known from practically every region that has a good early with Pediomeryx, but Webb (1983) and Janis and Manning (1998) placed Barstovian record. Sinclairomeryx riparius occurs in Nebraska and Pediomeryx in a separate subgenus, Pediomeryx (Pediomeryx), to accom- Saskatchewan; Drepanomeryx falciformis is known from Nebraska and modate the specimens that Stirton originally placed in that genus. As Texas; Rakomeryx sinclairi occurs in Nebraska and California; Janis and Manning (1998) point out, whether to place them in different Dromomeryx borealis in Nebraska, Montana, Oregon, Nevada, New subgenera of the same genus, or recognize two genera, is largely a matter Mexico, and Colorado; Subdromomeryx antilopinus is found in Texas 296

FIGURE 22. Temporal ranges of valid dromomerycine taxa, plotted against the time scale of the North American land mammal ages (NALMA), after Tedford et al. (2004) and Janis and Manning (1998). Solid line terminated by arrows shows known temporal ranges; dashed line shows inferred temporal ranges (based on cladogram in Fig. 2) and ghost lineages. “Lt. Arikaree.” = Late Arikareean; “Hemingf.” = Hemingfordian; “Clarend.” = Clarendonian. only; Bouromeryx americanus from Nebraska, Montana, California, unicornis plus the new taxon Yumaceras are known. C. unicornis is still Florida, Colorado, and Texas; Cranioceras unicornis from Nebraska only; found in Nebraska and California, while Yumaceras figginsi occurs in and Cranioceras teres from New Mexico (plus the unnamed new species Colorado, Texas, and Nebraska, Y. hamiltoni in Florida, and Y. ruminalis from the Caliente Formation of California, fide Kelly and Lander, 1988). in California. In the late Hemphillian, Cranioceras and Yumaceras van- In the late Barstovian, diversity was still very high. Sinclairomeryx, ished, and only a single species, Pediomeryx hemphillensis, survived. Subdromomeryx, and Drepanomeryx vanished, but Rakomeryx sinclairi, But it was very widespread, being known from late Hemphillian beds in Dromomeryx borealis, Bouromeryx americanus, Cranioceras unicornis, Florida, California, Oklahoma, Texas, and Nebraska. This drop in diver- and C. teres persisted, and the primitive Procranioceras skinneri ap- sity from the late Clarendonian through the Hemphillian is consistent peared (much later than its presumed descendant, Cranioceras). This with the data plotted by Janis (2000, fig. 3.5). diversity of 5 genera and 6 species is much higher than the diversity The great reduction in diversity of valid species also affects other values shown by Janis (2000, fig. 3.5). The geographic spread of these studies that were based on the old, oversplit taxonomy of Frick (1937). taxa is still high, too. Rakomeryx sinclairi occurs in Oregon and Mon- More than half of the dromomerycine species cited in Alroy’s North tana; Dromomeryx borealis is found in Nebraska, Colorado, Wyoming, American mammalian database (http://www.nceas.ucsb.edu/~alroy/ Nevada, and California; Bouromeryx americanus is known from Ne- nafmsd.html) are invalid, casting doubt on the overall validity of such braska, Texas, and Montana; Procranioceras skinneri occurs in Ne- “taxon counting” studies which use outdated taxonomy to draw general braska and Saskatchewan; Cranioceras unicornis was found in Nebraska conclusions about mammalian evolution. The problem is equally severe only, and C. teres in New Mexico only. in the moschids (Prothero, this volume), and in the oreodonts, pronghorns, By the early Clarendonian, diversity had dropped dramatically. and camels, so a significant portion of such databases cannot be trusted Only Dromomeryx borealis, Cranioceras unicornis, and C. teres are because the taxonomy of North American mammals is not suffi- known, but this is still a higher generic and specific diversity than shown ciently updated to make such surveys worthwhile. Although Alroy (2002, by Janis (2000, fig. 3.5). The geographic spread of the group was also 2003) has begun to acknowledge the problem, it runs deeper than he reduced. No dromomerycines are known from Montana, Sasatchewan, realizes, and casts doubt on the whole process of taxon counting. Oregon or Florida (although beds of this age are rare in these regions). D. CONCLUSIONS borealis occurred in California and South Dakota; Cranioceras unicornis in Nebraska only, and C. teres is known from New Mexico, Texas, South From 49 named species and over a dozen genera and subgenera Dakota, and California. recognized by Frick (1937) in the subfamily Dromomerycinae and In the late Clarendonian and early Hemphillian, only Cranioceras Aletomerycinae, we recognize only 18 valid species in 12 genera. Most 297 of Frick’s (1937) taxa can be synonymized because he failed to account declined dramatically, so that by the late Hemphillian, only one species, for populational variation, or failed to diagnose his taxa adequately. With Pediomeryx hemphillensis, is known, although it occurred in late an updated taxonomy of the Dromomerycinae, a much clearer under- Hemphillian beds in Florida, California, Oklahoma, Texas, and Nebraska. standing of their diversity and biogeographic distribution emerges. In- stead of the orthogenetic sequence presented by Webb (1983, fig. 1), the ACKNOWLEDGMENTS group has a very bushy phylogeny, with multiple contemporaneous We thank M. Mihlbachler, J. O’Connor, F. Sanchez, and J. Ludtke lineages, and several ghost lineages where more primitive taxa (e.g., for help with this project in the AMNH. We thank E. Manning and B. Drepanomeryx, Procranioceras) appeared later than their supposed Taylor for all their curations and initial identifications of the material in descendants. A minimum of two immigration events from Eurasia (bring- the AMNH and F:AM collections that made this study possible. We ing the aletomerycins and the cranioceratins in the latest Arikareean at thank T. LeVelle for her painstaking weeks of work masking and silhou- 18-20 Ma) established the group in North America, after which they etting all the photographs. We thank J. Meng, C. Norris, and J.J. Flynn underwent rapid evolution to peaks of diversity in the late Hemingfordian for access to the AMNH and F:AM specimens, and J. Kelly for prepar- (6 genera, 7 species) and early Barstovian (7 genera, 8 species). During ing critical specimens from asbestos quarantine. We thank C. Janis, E. these times, they were also extremely widespread in North America, Manning, T. Kelly, G. Semprebon, D. Whistler, and S. Lucas for critical occurring in just about every region that has beds of that age. In the reviews of the manuscript. This research was supported by grants to Clarendonian and Hemphillian, their diversity and geographic spread Prothero by the Donors of the Petroleum Research Fund of the American Chemical Society, and by NSF grant 03-09538. REFERENCES

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