Blancan Camelids from San Miguel De Allende, Guanajuato, Central Me´ Xico

BLANCAN CAMELIDS FROM SAN MIGUEL DE ALLENDE, GUANAJUATO, CENTRAL ME´ XICO

E. JIME´ NEZ-HIDALGO1 AND O. CARRANZA-CASTAN˜ EDA2 1Universidad del Mar, Campus Puerto Escondido, Instituto de Recursos, Km. 2.5 Carretera Puerto Escondido-Oaxaca, Puerto Escondido, Oaxaca 71980, Me´xico; and 2Centro de Geociencias, Campus Juriquilla, Universidad Nacional Auto´noma de Me´xico, Juriquilla, Quere´taro 76230, Me´xico, ,[email protected].

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J. Paleont., 84(1), 2010, pp. 51–65 Copyright ’ 2010, The Paleontological Society 0022-3360/10/0084-0051$03.00

BLANCAN CAMELIDS FROM SAN MIGUEL DE ALLENDE, GUANAJUATO, CENTRAL ME´ XICO

ABSTRACT—During the Pliocene, the diversification of the tribes Lamini and Camelini of the Family Camelidae took place in most of North America, but at present in Mexico the systematics of Pliocene Camelidae are poorly known. Fossil material described in this paper was recovered from Blancan I and Blancan III age floodplain and point bar deposits of the San Miguel de Allende basin, Guanajuato state, central Mexico, which approximately spans a time frame from 4.7 to 3.0 Ma. The identified taxa include the lamines Hemiauchenia blancoensis (Meade) 1945, Hemiauchenia gracilis Meachen, 2005, Blancocamelus meadei Dalquest, 1975 and Camelops sp., while the camelines are represented by Megatylopus sp. The records of H. gracilis and B. meadei in the Pliocene of central Mexico are the oldest in North America. Previous studies of the probable feeding strategies of these taxa indicate that they were browsers or browser-like intermediate feeders and just one was an intermediate feeder. The records of these species in the Early Blancan of Guanajuato extend their geographic distribution from the southern USA to central Mexico.

INTRODUCTION fauna (l.f.), Baja California Sur (Miller, 1980); Camelops sp. S CURRENTLY defined, the Blancan North American was identified in the Blancan Miraflores l.f. of Baja California A Land Mammal Age spans from around 4.8 Ma to about Sur, Las Arcinas l.f. of Hidalgo state and in the Late Blancan 1.72 Ma or even 1.35 Ma in youngest Blancan faunas, Tecolotlań l.f. of Jalisco (Carranza-Castan˜eda and Miller, covering almost all of the Pliocene and including the earliest 1998, Carranza-Castan˜eda and Miller, 2002); unidentified Pleistocene (Bell et al., 2004). camelid material was reported in the Early Blancan La Goleta In general, the North American Blancan mammal faunas l.f. of Michoacań; and cf. Camelops sp. has been mentioned in were less diverse than in previous mammal ages and some the Blancan fauna of San Miguel de Allende, Guanajuato taxa, such as protoceratids and rhinoceroses, vanished, while (Carranza-Castan˜eda and Miller, 2000). others, such as equids, canids, and gomphotheres, drastically The purpose of this paper is to describe the fossil camelid diminished their number of species (Janis et al., 1998). The material collected from several Blancan localities of San Late Blancan has been considered the age when South Miguel de Allende, Guanajuato and to discuss the paleobio- American immigrant taxa were integrated into the North logical significance of the identified taxa. American faunas at around 2.8 Ma (Webb, 1985, 1997; White GEOLOGIC SETTING AND GEOCHRONOLOGY and Morgan, 2005), but recent fossil discoveries and the The San Miguel de Allende basin is in the northeastern part geochronology developed in San Miguel de Allende indicates of Guanajuato state, between 20u559–21u069 Lat N and that such faunal mixing began earlier than previously believed 100u509–100u419 Long W (Fig. 1). The studied specimens were (Carranza-Castan˜eda and Miller, 2004; Flynn et al., 2005; collected from fine-grained floodplain and point bar deposits Woodburne et al., 2006). Several mammalian taxa that of the informal lithostratigraphic unit named upper Rancho participated in the Great American Biotic Interchange appear Viejo beds (Carranza-Castan˜eda et al., 1994; Jimeńez-Hidalgo earlier in the Blancan faunas of central Mexico when et al., 2004; Flynn et al., 2005). compared with those of temperate North America, such as Additional radioisotopic dates and new magnetostrati- glyptodont, ground sloth, pampatheres, capybara and skunk graphic data of the San Miguel de Allende sequence were among others (Flynn et al., 2005; Carranza-Castan˜eda, 2006; recently published, making it one of the most precisely age- Wang and Carranza-Castan˜eda, 2008). calibrated sequences in North America spanning the Hem- Regarding artiodactyls, the diversification of the tribes phillian-Blancan boundary. The ten localities with Blancan Camelini (that includes the dromedary and bactrian camel) camelid fossils spans approximately 4.7 to 3.0 Ma (Kowallis et and Lamini (that includes the alpacas, guanacos, llamas and al., 1998; Flynn et al., 2005; Adams et al., 2006) (Table 1). vicunãs) of the Family Camelidae took place for the most part In previous papers concerning the San Miguel de Allende in North America during the Pliocene (Honey et al., 1998; area, informal notation of locality numbers were used, but in Webb and Meachen, 2004). this paper we employ the registered numbers of the Localities Known North American Blancan camelids include the Catalogue of the Coleccioń Nacional de Paleontologıá, Museo Lamini genera Blancocamelus Dalquest, 1975, Hemiauchenia de Paleontologıá, Instituto de Geologıá, UNAM (when they Gervais and Ameghino, 1880 and Camelops Leidy, 1854, and are available). the Camelini Megatylopus Matthew and Cook, 1909, Titano- Fossil localities are 12 to 20 km north of the city of San tylopus Barbour and Schultz, 1934, and Gigantocamelus Miguel de Allende (Fig. 1). Barbour and Schultz, 1939 (Honey et al., 1998). Nearly all The associated fauna and geochronology indicates a of their records come from USA faunas. Blancan I and Blancan III age (Bell et al., 2004) or an Early In Mexico, fossils of cf. Hemiauchenia sp. and cf. Camelops Blancan age (Lundelius et al., 1987; Janis et al., 1998) for the sp. were described from the Late Blancan Las Tunas local fossil-bearing beds, from around 4.7 Ma to 3.0 Ma. The fauna 51 52 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

TABLE 1—Geochronology of the San Miguel de Allende localities that bear Blancan camelids (data taken from Flynn et al., 2005; Adams et al., 2006).

Locality number Radioisotopic date (Ma) Chron 3009 at Los Corrales 4.6 6 0.3 (FT) .C3n1r or C3n 2r 4.7 6 0.14 (40Ar/39Ar) 3077 ..Bottom C2An.1n 3074 3.3 6 0.1 (40Ar/39Ar) .C2An.3n 3.6 (FT) 3467 ..C2An.3n 3468 3.9 6 0.3 (FT) .Top C2Ar 3076 ..Top C2An.3n to bottom C2An.2r 3522 ..Bottom C2An.2r 3524 ..Middle C2An.3n 3529 and 3534 ..C2An.3n

(UF), with descriptions and illustrations of specimens housed at the American Museum of Natural History (AMNH); Museum of Paleontology, University of California (UCMP); Texas Tech University (TTU-P); the University of Kansas (KU); the Vertebrate Paleontology Laboratory Collection, University of Texas at Austin (TMM); and at the University of Nebraska State Museum (UNSM). The nomenclature used for deciduous dentition is that described in Loring and Wood (1969), while nomenclature for permanent dentition follows Honey (2004). The measurements of upper and lower dentition were taken with a caliper as maximum lengths and widths at occlusal level, and crown height was taken along the mesostyle or metastylid (Harrison, 1979; Janis, 1990). Limb measurements are maximum widths and lengths (Breyer, 1974, 1983; Harrison, 1979). Classifica- tion of lower tooth wear stages follows Breyer (1977). All measurements are expressed in millimetres (mm). Upper and lower teeth are represented by upper and lower case: I/i (incisor), C/c (canine), P/p (premolar), M/m (molar), D/d (deciduous tooth). Measurement abbreviations are: L, length; W, width; CH, crown height; PW, proximal width; DW, distal width; Kg, kilogram. Additional abbreviations include: FT, Fission-track; Gto, Guanajuato; USA, United States of America; l.f., local fauna; Ka, thousand years; Ma, million years.

FIGURE 1—Index map and geologic map of the San Miguel de Allende SYSTEMATIC PALEONTOLOGY area showing Blancan age localities where camelid speimens were RTIODACTYLA recovered. Geologic map modified from Adams et al. (2006). Order A Owen, 1848 Suborder TYLOPODA Illiger, 1811 Family CAMELIDAE Gray, 1821 recovered from the same beds where the studied material was Tribe LAMINI Webb, 1965 collected includes several species of South American immi- Genus HEMIAUCHENIA Gervais and Ameghino, 1880 grants, lagomorphs, rodents, a canid, a mustelid and a felid, as HEMIAUCHENIA BLANCOENSIS (Meade, 1945) well as a peccary, antilocaprids, equids and a gomphothere Figure 2, Tables 2, 3 (Carranza-Castan˜eda and Miller, 2000; Jimeńez-Hidalgo et al., 2004; Carranza-Castan˜eda, 2006). Tanupolama cf. T. longurio Hay; GAZIN, 1942, p. 475. Tanupolama blancoensis MEADE, 1945, p. 535, pl. 55; HIB- MATERIALS AND METHODS BARD AND RIGGS, 1949, p. 855, pl. 4. The fossil material described in this paper consists of Hemiauchenia blancoensis (Meade, 1945). WEBB, 1974, p. 200. isolated upper and lower cheek teeth, maxillary fragments Hemiauchenia macrocephala (Cope, 1893) DALQUEST, 1992, with teeth, rami fragments with teeth, and limb elements p. 293. (mainly astragali, metapodials and phalanges). They were Hemiauchenia blancoensis (Meade, 1945). HONEY et al., 1998, collected through surface pickup, and large elements were p. 454. recovered in plaster jackets. Diagnosis.—Occlusal length of the lower tooth row longer The fossils were prepared at Instituto de Geologıá (IGM), than in H. macrocephala in an equivalent stage of wear, Universidad Nacional Autońoma de Me´xico (UNAM), Me´xico mandibular diastema shorter than in H. macrocephala, longer City, using standard techniques. This institution is also the than in Pleiolama vera (Matthew) 1909 (this species was repository of all the collected specimens under the IGM. formerly included in Hemiauchenia); canine laterally com- Comparisons of specimens were made with those at the pressed and situated immediately behind i3, p1 caniniform, Florida Museum of Natural History, University of Florida separated from the canine by a short diastema, p2 absent, p3 JIMEŃEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 53

FIGURE 2—Hemiauchenia blancoensis (Meade, 1945) from the Blancan I and Blancan III of San Miguel de Allende, Guanajuato. IGM 2329, maxillary fragment with right DP2–M1 and left DP2–M2: 1, occlusal view (rostral side toward right page margin); 2, labial view (rostral side toward left page margin). IGM 2331, right P4: 3, occlusal view. IGM 2346, mandible with p3–m3 and alveoli for c and i: 4, lateral view; 5, cheek teeth in occlusal view. IGM 2344-1, right mandible fragment with dp3–m1: 6, lateral view; 7, occlusal view (reversed). IGM 2339 left astragalus: 8, anterior view; 9, posterior view. IGM 2338, pedal phalanx: 10, anterior view; 11, posterior view. Excepting IGM 2331 right P4 in which scale 5 1 cm, all other specimens scale 5 3 cm. 54 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

TABLE 2—Measurements (in mm) of upper teeth of Hemiauchenia blancoensis from San Miguel de Allende and other Blancan localities from USA.

Specimen Tooth Measurement IGM 2329* IGM 2332 IGM 2341 IGM 2342-1 IGM 2342-2 TMM 31176-5 KU 71141 DP2 L 11.0/9.4 ...... W 7.3/7.0 ...... DP3 L 21.5 /20.8 .... 20.3 . W 15.9/16.3 .... 14.7 . DP4 L 23.7/23.5 .... 21.6 . W 18.2/18 .... 17.5 . M1 L 30.6/30.1 24.3 26.6 .. 29.4 28 W . 14.6 14.2 .. 21 18 M2 L 29.2/15.2 .. 21.5 . 32.2 29 W ... 18.7 . 20 14 M3 L .... 25.6 . 27.4 W .... 17.5 . 15.4 *First value is for right teeth and second is for left teeth. variably present and with two roots; hypsodonty of cheek coronoid process is long, straight, half as wide as the teeth intermediate between P. vera and H. macrocephala; limbs ascending ramus, and is somewhat weak. The alveoli for the very long and slender (Hibbard and Riggs, 1949; Webb, 1974; i1 are ovoid with the longer axis dorsoventrally oriented; those Breyer, 1977; Honey et al., 1998). of i2 have a triangular outline with rounded tips, and those for Description.—The anterior palatine foramina of the maxil- i3 and c are ovoid with their major axis anteroposteriorly lary fragment IGM 2329 are located at the level of the rear oriented. The alveolus for the p1 is also ovoid. It is situated part of DP3; the suture between the maxillary and the palatine above the mental foramen and is separated from the alveolus is U-shaped, and its anterior margin is at the anterior portion for the canine by a diastema of 11.5 mm in length in the left of M1 (Fig. 2.1). Both DP2 are small, longer than wide, and ramus and of 10.0 mm in the right ramus. The cheek teeth of have a well developed anterior crest and central rib. The DP3s IGM 2346 are in wear stage IV. Both p3 are laterally are trilobate, molariform, and have well-developed ribs and compressed and have two roots and a small fossettid on their styles. The DP4s are molariform, the parastyle and metastyle posterior part. The p4 are wedge-shaped and have an ovoid are moderately developed while the mesostyle is well fossetid on the posterior area and a moderately opened developed; the fossettes are deep. M1 and M2 have well- anterolingual fold that brackets the paraconid. In the m1, the developed styles and ribs and have U-shaped deep fossettes; anterolabial stylid (‘‘llama buttress’’) and the metastylid are these characters are also present in M1, IGM 2341. Both M1 slightly developed, while the parastylid and entostylid are of the maxillary fragment are slightly worn while M2 is absent. In the m2, parastylid and anterolabial stylid are faintly unworn (Fig. 2.1, 2.2). The P4, IGM 2331 (length 17.5 mm, developed, and the metastylid is moderately developed. The width 15.7 mm), has three roots, a half-moon outline and a m3 have a well-developed talonid and slightly-developed large and open U-shaped fossette (Fig. 2.3); its parastyle is stylids and ribs (Fig. 2.5). well developed. M1, IGM 2332, is in wear stage III, has a well The less worn isolated molars IGM 2328, IGM 2340, IGM developed parastyle, mesostyle, and anterior rib but a weak 2327, and IGM 2335 have better developed stylids and ribs metastyle. M2, IGM 2342-1, M3 IGM 2342-2, and IGCU than those of IGM 2346. 5942, are in wear stage IV, and their ribs and styles are The rami fragments IGM 2343, IGM 2344-1 (Fig. 2.6, 2.7), moderately developed. and IGM 2344-2 bear deciduous dentition. The dp3 has two roots In mandible IGM 2346, the dorsal border of the diastema is and its morphology is similar to the p4; the dp4 has three roots, sharp and has a length of 44.5 mm between the alveolus of p1 and the anterior stylid is strongly developed while the middle and and the p3. The ventral border of the mandible is straight posterior stylids are moderately developed. The unworn m1 is (Fig. 2.4), and its depth is 67 mm at the m3 level. The hypsodont (CH 5 34 mm) and has well-developed stylids.

TABLE 3—Measurements (in mm) of lower teeth of Hemiauchenia blancoensis from San Miguel de Allende and other Blancan localities from USA.

Specimen IGM IGM IGM IGM IGM IGM IGM KU UNSM TMM Tooth Measurement IGM 2346* 2327 2328 2335 2340 2343 2344-1 2344-2 7500 4707-39 31181-126 dp3 L ...... 15 14 16.5 .. W ...... 7.3 6 7 .. dp4 L .....27.6 31 31.4 33.7 .. W .....8.1 10.4 11 11.8 .. p4 L 18.6/18.7 ...... 16 18 W 10.5/10.3 ...... 7 8.9 m1 L 21.3/20.9 . 22 . 28 25.5 29.4 30 . 18.7 26.6 W 17.5/17.7 . 14.7 . 12.6 7.4 10.7 10.4 . 15 15.4 m2 L 23/24.2 30 ...... 27.5 32.5 W 18.4/17.9 15 ...... 14 16.8 m3 L 36/35 .. 38.4 ..... 38.8 40 W 17.9/17.3 .. 16 ..... 10.6 15 p4-m3 . 98.9 ...... 95.7 115 *First value is for right teeth and second is for left teeth. JIME´NEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 55

The i3 of IGM 2345 is procumbent, has a triangular outline, Discussion.—The above described material from San Miguel and its middle and dorsal portions are flat while the ventral de Allende shows the diagnostic features of H. blancoensis and one is convex and the lateral one is sharp. The canine is small is close in morphology and size when compared with and laterally compressed. specimens assigned to this species from the USA Blancan The radius-ulna IGM 2336 is long and slender (length faunas. The teeth of the maxillary fragment IGM 2329 have a 470 mm, proximal articular width 68.4 mm, distal articular similar size (Table 2) and well-developed styles and ribs, as width 73.0 mm); its olecranon process is missing except for the well as a similar shape and depth of fossettes compared with basal portion; the lateral tuberosity is anteromedial and the paratype of H. blancoensis TMM 31176-5, a partial right moderately developed; the bicipital rugosity is well marked maxillary with DP3-M2. and circular in outline; the proximal interosseous foramen is P4 IGM 2331, M1 IGM 2332, M2 IGM 2342-1 and M3 narrow and elongated. The distal epiphysis is lost, and the IGM 2342-2, as well as IGCU 5942, show a similar size distal part of the ulna is not completely fused, which indicates (Table 2) and well- to moderately-developed styles and ribs, as a young individual. has been reported in specimens of the upper teeth of H. The proximal fragment of tibia IGM 2330 is slender, its blancoensis in a similar wear stage (Hibbard and Riggs, 1949; lateral condyle is wider than the medial, and the sulcus Webb, 1974). The subtle differences in length and width muscularis is moderately wide and deep. between the specimens from Guanajuato and those from The lateral condyle of astragali IGM 2337 (lateral length Texas and Kansas are related to the stage of wear in those 54 mm, medial length 47.8 mm, distal width 39.6 mm) and molars. Breyer (1977) observed that with increased wear, IGM 2339 (lateral length 50.7 mm, medial length 47.3 mm, anterior-posterior attrition between molars occurs, diminish- distal width 34.6 mm) is higher and narrower than the medial ing length and increasing their width. condyle. The tibial valley is narrow. The medial condyle does Mandible IGM 2346 and its teeth display the diagnostic not overhang the sustentacular surface, and the interarticular characters of the species, which were enumerated above in the fossa is deep and rounded in outline (Fig. 2.8, 2.9). The fibular diagnosis. The dimensions of its teeth as well as its p4-m3 salient is prominent; the medial edge of the sustentacular facet length are close to those from specimens in wear stage IV is continuous with that of the navicular trochlea, forming a (Breyer, 1977), such as UNSM 4707-39 (Table 3) and UNSM smooth curve. The interarticular fossa is deep and not ovoid in 21382 from Broadwater l.f. The degree of development of outline. The navicular and cuboid facets are similar in size. stylids and hypsodonty between the specimens is also similar. Proximal phalanges IGM 2333 and IGM 2338 are slender Size differences between the teeth from San Miguel and the with a straight shaft. Their proximal articulating surface is holotype TMM 31181-126, from the Blanco l.f. of Texas, can transversely narrow, dorsoventrally high and slightly concave. be attributed to differences in wear stage; IGM 2346 is in wear The carinal groove is narrow and shallow; the attachment scar stage IV and the holotype is in wear stage II or III. for the suspensory ligament extends distally about 26% the Both dp3 and dp4 of rami fragments IGM 2343, IGM 2344- shaft length. The distal trochlea is narrow and the dorsal 1, and IGM 2344-2 have a similar morphology to the extent of the articulation surface is short (Fig. 2.10, 2.11). deciduous premolars of KU 7500, a mandible fragment from Distally, in the shaft’s ventral side of IGM 2338 there are three Keefe Canyon l.f. identified as H. blancoensis. The dp3s have a parallel striations that seem to represent predation marks triangular outline and a small posteriorly situated fossettid, (Fig. 2.11). Second phalanx IGM 2334 (length 46.4 mm, and the dp4s have a strongly developed anterior stylid and a proximal width 25 mm) is short and the shaft has a triangular less prominent medium and posterior stylids. Also, the size of outline. Its proximal articular surface is dorsoventrally the premolars is similar (Table 3). concave and wider than its height. The teeth of IGM 2345 are similar to those of specimen Material examined.—From locality 3009 Arroyo La Carreta UNSM 21382, a mandible from the Broadwater l.f. assigned at Los Corrales section: IGM 2327, left m2. From locality to H. blancoensis; in both, the i3 is procumbent and spatulate 3077 Arroyo El Tanque: IGM 2328, left m1; IGM 2329 and the canine is laterally compressed and recurved and is of maxillary fragment with right DP2-M1 and left DP2–M2; comparable size. IGM 2330, left proximal tibia fragment. From locality 3074 Regarding the postcranial elements, tibia fragment IGM Arrastracaballos: IGM 2331, right P4; IGM 2332, left M1; 2330 displays the slender proportions and the characteristic IGM 2333, pedal phalanx I and IGM 2334, phalanx II. From medium size of H. blancoensis. Radius-ulna IGM 2336 is also locality 3467 Garbani: IGM 2335, left m3; IGM 2336, left slender, and its size is similar to KU 7491 (length 550 mm, radius-ulna. From locality 3468 La Pantera B: IGM 2337, left distal articular width 63 mm) from Keefe Canyon l.f. Also, in astragalus. From locality 3076 Cuesta Blanca: IGM 2338, both specimens the ulna is almost completely co-ossified at the pedal phalanx I. From locality 3522 Pa´jaro Grande: IGM distal portion. 2339, left astragalus. From locality 3524 Porkchop: IGM Breyer (1974) described morphological features present in 2340, left m1; IGM 2341, right M1; IGM 2342-1 and IGM an astragalus sample associated with mandibles of H. 2342-2, right M2 and M3 of one individual; IGM 2343, left blancoensis from Broadwater and Lisco l.f. These features mandible fragment with dp4–m1; IGM 2344-1, right mandible are also present in both astragali from Guanajuato, such as a fragment with dp3–m1 and IGM 2344-2, left mandible prominent medial condyle that does not overhang the fragment with dp3–m1, both of a single individual; IGM sustentacular facet, the medial edge of the sustentacular facet 2345, right symphysis fragment with i3 and c. From locality continuous with that of the navicular trochlea, and the tibial 3534 Pecos: IGM 2346, mandible with right and left p3–m3 ligament surface parallel to the medial articular surfaces. Also, and the alveoli for i1–i3, c, and the p1. the dimension of the specimens from Guanajuato are similar Occurrence.—Early Blancan of Kansas, New Mexico, Texas to the mean dimensions from the Nebraska localities (mean and Washington; Late Blancan of Arizona, Colorado, New lateral length 57–59 mm, mean medial length 44–46 mm). The Mexico, Nebraska, Kansas, Texas, Florida; Irvingtonian of slight differences between the two sets could be explained by Texas (Honey et al., 1998; Morgan and Lucas, 2003). Early taking into account intraspecific variation and the age of the Blancan or Blancan I and Blancan III of Guanajuato. organisms. Breyer (1974) also described the proximal phalanges; 56 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

TABLE 4—Measurements (in mm) of upper teeth of Hemiauchenia gracilis from the Blancan of San Miguel de Allende and Florida. *Maxillary fragments with teeth.

Specimen Tooth L W CH IGM 8817-1 M1 18.2 14.6 19.7 IGM 8817-2 M3 22 15 20.5 UF 45493* M1 17.8 12.7 7.1 UF 45493* M2 22.2 15.7 19.5 UF 210714* M1 21.8 14.3 11.4

Hemiauchenia species since, as Breyer (1977) noted, cheek teeth dimensions vary according to wear stage, so it is important to compare teeth in the same stage of wear, as was first recommended years ago (Breyer, 1977; Montellano, 1989; Webb and Meachen, 2004). Also, the length of the diastema is just one of a set of characters states used in the identification of the several Hemiauchenia species (see diagnosis section above) and it is precisely the combination of such characters states—not just diastema length—that allow a reliable identification among the species of the genus. Subsequently, we consider Hemiauchenia blancoensis a valid species distinct from H. macrocephala, as do other authors also (Honey et al., 1998; Hulbert and Webb, 2001). The record of H. blancoensis in the Blancan I and III of San Miguel de Allende represents the first occurrence outside of the USA (Jime´nez-Hidalgo and Carranza-Castan˜eda, 2002).

HEMIAUCHENIA GRACILIS Meachen, 2005 Figure 3; Tables 4–6 Diagnosis.—Considerably smaller than Hemiauchenia blancoensis, ‘‘Hemiauchenia’’ minima (Leidy) 1886 and Pleiolama vera; lacks p1 and p3; postcranial elements more slender than those of H. macrocephala and longer and usually more robust than those of Hemiauchenia edensis (Frick) 1921 (Meachen, FIGURE 3—Hemiauchenia gracilis Meachen, 2005 from the Blancan III 2005). Shares homologous character states with Hemiachenia of San Miguel de Allende, Guanajuato. IGM 8817-1, M1: 1, occlusal view. IGM 8817-2, M3: 2, occlusal view. Scale 5 1 cm. IGM 8818, left macrocephala and Hemiauchenia edensis, such as gracile astragalus: 3, anterior view; 4, posterior view. IGM 8819, pedal phalanx: molars, slender postcranial elements, and small size. 5, anterior view; 6, posterior view. Scale 5 3 cm. Description.—IGM 8817-1 M1 lacks the anterior fossette but has a U-shaped posterior one; the parastyle and mesostyle similarities observed in the specimens from San Miguel de are well developed; its metastyle is less developed (Fig. 3.1). Allende include (1) slender elements with a straight shaft, (2) IGM 8817-2 M3 has U-shaped fossettes and well-developed lateral and medial ventral trochleae nearly equal in length and parastyle and mesostyle (Fig. 3.2). Molars are small (Table 4), extending dorsally to the shaft, and (3) divided distal part of the moderately hypsodont, their styles are equal in length to the scar for the insertion of the suspensory ligament. Hibbard and crown height, and both teeth are completely covered with a Riggs (1949) observed these features in a set of first phalanges layer of cementum. from Keefe Canyon l.f. that they assigned to H. blancoensis. Astragalus IGM 8818 is small (Table 5), and its lateral Dimensions of the San Miguel specimens (IGM 2333: length condyle is higher and narrower than the medial one. The 103 mm, proximal width 27.1 mm; IGM 2338: length 101 mm, interarticular fossa is deep and rounded in outline, the medial proximal width 27.6 mm) are very close to the ones reported by condyle does not overhang the sustentacular facet, the fibular Breyer (1974) (mean length 96 mm, mean proximal width salient is very prominent (Fig. 3.3, 3.4), and the navicular 28 mm) and Hibbard and Riggs (length range 84–108 mm). trochlea is continuous with the sustentacular facet. On the The second phalanx IGM 2334 is close in size to a specimen plantar side of the astragalus there is a very deep and rounded assigned to H. blancoensis by Hibbard and Riggs (1949) and notch. has the morphology of lamine camels (Webb, 1965); it is short with a wedge-shaped transverse section, and the ventral trochlea is not splayed out laterally. Because of these characters and the medium size of the specimen, it is referred TABLE 5—Measurements (in mm) of the astragali of Hemiauchenia gracilis from San Miguel de Allende, Guanajuato and Florida. [Data of UF to H. blancoensis. specimens taken from Meachen (2003)]. Dalquest (1992) synonymised Hemiauchenia blancoensis with H. macrocephala because he observed that the range of Specimen L W the diastema’s length between the two species overlapped and IGM 8818 41.5 26.6 because, according to him, cheek teeth are almost useless for UF 210722 38.0 24.1 taxonomy, since they become shorter and broader with wear. UF 10281 40.4 25.4 We do not share his opinion regarding the synonymy of both UF 210706 38.6 24.3 JIME´NEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 57

TABLE 6—Measurements (in mm) of the proximal phalanges of Hemiauchenia gracilis from San Miguel de Allende, Guanajuato and Florida. [Data of UF specimens taken from Meachen (2003)].

Specimen L PW DW IGM 8819 63.0 19.0 15.2 UF 210704 66.2 17.7 14.1 UF 210703 67.7 18.1 14.5 UF 18237 71.2 17.8 14.4 UF 210712 67.9 18.1 14.9

Phalanx I IGM 8819 is small and slender (Fig. 3.5, 3.6); its shaft is straight and somewhat triangular in outline; the proximal articulating surface is narrow, dorsoventrally high, and slightly concave; the carinal groove is narrow and shallow; the attachment scar for the suspensory ligament extends distally about 22% the shaft length and has an asymmetrical ‘‘W’’ shape. The distal trochlea is narrow. FIGURE 4—Blancocamelus meadei Dalquest, 1975 from the Blancan III Material examined.—From locality 3077 Arroyo El Tanque: of San Miguel de Allende, Guanajuato. IGM 8820, pedal phalanx: 1, anterior view; 2, posterior view. Scale 5 3 cm. IGM 8817-1 and IGM 8817-2, right M1 and M3 of a single individual. From locality 3524 Porkchop: IGM 8818, left astragalus; IGM 8819 phalanx I. and not laterally splayed. The slight differences between the Occurrence.—Late to latest Blancan (2.5–1.8 Ma) of Flor- phalanx length from Guanajuato and Florida can be explained ida (Meachen, 2005); Late Blancan of Arizona and New by taking into account intraspecific variation, sexual dimor- Mexico (White and Morgan, 2005) and Early Blancan or phism, and the age of the organisms. Blancan III of Guanajuato. The material from San Miguel de Allende shows the Discussion.—Montellano (1989) assigned a mandible, a diagnostic features of Hemiauchenia gracilis, such as small maxillary fragment, and two astragali from the late Hemphil- size, slender postcranial elements, and gracile molars. They lian of San Miguel de Allende to Hemiauchenia sp., remarking also have a morphology similar to specimens assigned to this that they represent a smaller form than Pleiolama vera (the species. For these reasons they are assigned to H. gracilis. specimens are 30–40% smaller). Molars M1 and M3 from the Besides H. gracilis there is another small species of Blancan of San Miguel de Allende differ from those of the Hemiauchenia reported from several late Hemphillian faunas maxillary fragment in the greater development of the styles, of southern USA and northern and central Mexico (Mon- especially the mesostyle, and in that the Blancan molars are tellano, 1989; Jime´nez-Hidalgo and Carranza-Castan˜eda, completely covered with a layer of cementum. Astragalus 2005; Meachen, 2005; Webb et al., 2008). Preliminary study IGM 8818 is morphologically close to the astragali described of this small lamini from the Hemphillian of San Miguel de by Montellano (1989), but the Blancan specimen is about 6% Allende indicates that it can be referred to Hemiauchenia smaller. edensis. Webb et al. (2008) mentioned that H. edensis is also In 2005 Meachen described a new species of Hemiauchenia present in the Yepomera/Rincon fauna of Chihuahua. from the late Blancan of Florida that was originally thought to H. edensis and H. gracilis are morphologically similar, but be H. macrocephala (Meachen, 2005). differences in some character states as well as some dimensions The studied specimens from San Miguel de Allende share and ratios of the skeletal elements distinguish the two species. various characters with those of the new species from Florida, The Hemphillian H. edensis has a very shallow mandible Hemiauchenia gracilis. Upper molars IGM 8817-1 and IGM (depth at m3 is 34 mm), molars lack cement, crescents are V- 8817-2 have a well-developed parastyle and mesostyle shaped, lower molars are transversely compressed, the (Fig. 3.1, 3.2), as is observed in the M1 of UF 210714, a astragalus length/width ratio is 1.58 and the phalanx length/ maxillary fragment with P4 and M1 from DeSoto Shell Pit 5. width ratio is 6.1; meanwhile, in H. gracilis the mandible is Also, the teeth from Florida and Guanajuato are small and deep (depth at m3 is 43 mm), molars are covered with a layer moderately hypsodont (Table 4), gracile, all with U-shaped of cementum, molar crescents are U-shaped, the astragalus fossettes (Fig. 3.1, 3.2), and are covered with a complete layer length/width ratio is 1.47, and the phalanx length/width ratio of cementum. is approximately 7.1 (Meachen, 2005; Webb et al., 2008). Left astragalus IGM 8818 has a similar size (Table 5) and The presence of H. gracilis in the Early Blancan of San morphology to those of UF 210722, UF 10281, and UF Miguel de Allende, Guanajuato, is the first from Mexico. 210706, astragali assigned to H. gracilis (Meachen, 2003, Genus BLANCOCAMELUS Dalquest, 1975 2005). These specimens are significantly smaller than those of H. blancoensis and H. macrocephala; they have a very deep BLANCOCAMELUS MEADEI Dalquest, 1975 notch on their plantar side. Their length/width ratio is similar Figure 4, Table 7 [1.56 for IGM 8818 and a mean of 1.58 in specimens from Diagnosis.—Limb bones exceedingly long and relatively Florida (Meachen, 2005)]. The lateral condyle is higher and slender (Dalquest, 1975). Limbs, especially distal elements, narrower than the medial one, and the interarticular fossa is extremely elongated and slender as in Hemiauchenia and deep and rounded in outline. Aepycamelus giraffinus (Matthew in Matthew and Cook, 1909) Phalanx IGM 8819 is similar in size and morphology to pes but more than one and a half times as long as in Hemiauchenia phalanges of H. gracilis (Table 6). The specimens from (Honey et al., 1998). Guanajuato and Florida are slender and small, with a straight Description.—Proximal phalanx IGM 8820 is long and shaft of a triangular shape and a well-developed W-shaped slender (Table 7). Its proximal articulating surface is dorso- suspensory ligament scar. Their distal trochleae are narrow ventrally high and transversely narrow, and its carinal groove 58 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

TABLE 7—Measurements (in mm) of proximal phalanges of Blancocamelus meadei from Guanajuato and Texas.

Specimen L PW DW IGM 8820 137.0 37.2 33.0 TMM 31176-39 142.0 36.5 30.7 TMM 31176-39 141 36 30 TMM 31176-35 141 35 31.5 TTU-P 6421 135 38 31.8 is moderately deep. The attachment for the suspensory ligament is W-shaped, with one arm larger than the other, and occupies 32.8% of the phalanx’s length. The shaft is straight, slender, and higher than wide (Fig. 4). The distal trochlea is narrow. Material examined.—From locality 3074 Arrastracaballos: IGM 8820, phalanx I. Occurrence.—Late Blancan of Arizona, New Mexico and Texas (Honey et al., 1998; Morgan and Lucas, 2003; White and Morgan, 2005). Early Blancan or Blancan III of Guanajuato. Discussion.—IGM 8820 has proportions similar to phalanges I of Hemiauchenia blancoensis from San Miguel de Allende, although it is considerably larger (25.5%). The length/proximal width ratio in IGM 8820 is 3.68 while in IGM 2333 and IGM 2338 (both H. blancoensis) is 3.72. In this respect, Dalquest (1975) mentioned in the description and comparison of Blancocamelus meadei that their limb bones resemble those of H. blancoensis in proportions. By the same token, Harrison (1985) mentioned that the exceedingly long but quite slender limbs of B. meadei evoke a mental image of a FIGURE 5—Camelops sp. from the Blancan III of San Miguel de Allende, Guanajuato. IGM 8821, left astragalus: 1, anterior view; 2, giant Hemiauchenia. posterior view. Scale 5 3 cm. IGM 8822-2, left tibia: 3, posterior view; 4, Comparing the specimen from Guanajuato with the lateral view. IGM 8822-1, left femur fragment: 5, anterior view; 6, proximal phalanges of Titanotylopus, Gigantocamelus and posterior view. Scale 5 10 cm. Megatylopus, it is evident that IGM 8820 is significantly more slender and between 13%–6% longer (depending on the Description.—The lateral condyle of astragalus IGM 8821 is genus), than any proximal phalanges of those genera whose higher and narrower than the medial one. The tibial valley is phalanges are stouter and shorter (Dalquest, 1975; Voorhies very wide, and the interarticular fossa is deep and wide and Corner, 1986; Morgan and White, 2005). (Fig. 5.1, 5.2). The medial condyle is low; it does not overhang IGM 8820 shares many characters with the proximal the sustentacular surface, and posteriorly it has a well- phalanges of Blancocamelus meadei, such as a long and developed tuberosity. The tibial valley is separated from the slender shaft, a narrow proximal articulating surface and an sustentacular facet by a ‘‘step’’ which is better developed in the asymmetrical W-shaped scar for the attachment for the lateral portion of IGM 8821. The fibular salient is well suspensory ligament (Fig. 4). Also, it has dimensions similar developed (Fig. 5.1). The paracuboid facet is separated from to those of specimens of B. meadei (Table 7); in fact, it is just the fibular facet by a deep groove and continues dorsally to 3.5% smaller than TMM 31176-39, the largest phalanx the parasustentacular facet. The subsustentacular fossa is deep assigned to this species (Meade, 1945). and wide. The navicular facet is larger than the cuboid facet. The above-mentioned criteria allow the confident assign- Tibia IGM 8822-2 is relatively stout (Fig. 5.3, 5.4), the ment of the specimen from Guanajuato to Blancocamelus femoral facets of lateral and medial condyles are broad and meadei. The record of B. meadei in San Miguel de Allende is subequal in length, the sulcus muscularis is wide and deep, and the first one from Mexico (Jime´nez-Hidalgo and Carranza- the cnemial crest is moderately robust and occupies 27% of the Castan˜eda, 2006). shaft length. The tibial shaft is anteroposteriorly flattened. Its anterior and posterior surfaces meet in the lateral part of the Genus CAMELOPS Leidy, 1854 shaft, forming a sharp crest (Fig. 5.4). On the medial side, the CAMELOPS sp. anterior and posterior surfaces are separated by a flat surface Figure 5 that tapers distally. The medial malleollus and the anterome- Diagnosis.—Cheek teeth very hypsodont; I1-2 lost; I3 dial distal process are well developed. Distally, the lateral recurved and caniniform, larger than C1; C1/c1 very reduced groove is wider than the medial one, and both are widely and laterally compressed. c1–p4 diastemal crest very sharp; P1 separated by a well-developed crest. The length of IGM 8822-2 and P2/p2 lost; molars slender in relation to length; lower is 447 mm, its proximal width is 120 mm, its distal width is molars with anteroexternal stylids stronger than in Alforjas, 92 mm, and the anteroposterior distal length is 55.4 mm. weaker than in Lama, Palaeolama, or Hemiauchenia. Limbs Femur IGM 8822-1 lacks the proximal epiphysis. The long but stocky; metapodials robust and somewhat shortened; diaphysis is ovoid in transverse section, and in its posterome- proximal phalanges with raised suspensory ligament scar dial part it has a well marked linea alba; the fossa plantaris is extending almost to centre of shaft (Honey et al., 1998). evident. The medial condyle of the distal epiphysis is lower JIME´NEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 59 and less bulbous than the lateral condyle (Fig. 5.5, 5.6). The Dalquest, 1975a and Camelops huerfanensis (Cragin) 1892 intercondyloid fossa has a quadrangular outline. The medial (Harrison, 1985); so this variation in size could be considered condyle of the patellar trochlea is less developed than the as interspecific variation. lateral one; on the proximal side of this trochlea there is a deep Femur IGM 8822-1 has a well developed linea alba, its fossa. The intercondylar width of the specimen is 120 mm and medial condyle of the distal epiphysis is lower and less bulbous the width of the patellar area is 56.7 mm. than the lateral condyle and its intercondyloid fossa is closed Material examined.—From locality 3074 Arrastracaballos: squarely, as is observed in specimens assigned to Camelops, IGM 8821, left astragalus. From locality 3468 La Pantera B: and its dimensions are similar to those of femora assigned to IGM 8822-1, left femur fragment and IGM 8822-2, left tibia. the genus [observed range of patellar surface width 43–63 mm Occurrence.—Early Blancan of Washington, Idaho, Cali- (Webb, 1965, table 11)]. fornia, New Mexico, and Nebraska, and Early Blancan or Camelops traviswhitei was identified in the late Blancan Blancan III of San Miguel de Allende, Guanajuato; Late faunas of Arizona and Idaho (Thompson and White, 2003, Blancan of California, Nevada, Arizona, New Mexico, Texas, 2004); thus, it is possible that the fossil material from San South Dakota, and Baja California, Pleistocene of North Miguel de Allende could belong to this species. Mooser and America (Honey et al., 1998). Dalquest (1975a) mentioned in the diagnosis of C. traviswhitei Discussion.—Astragalus IGM 8821 is 25% larger than the that it is ‘‘A large camel, the size of or larger than C. H. blancoensis astragali from San Miguel de Allende and is hesternus…’’ and with relatively very short and stout stouter; its tibial valley is wider and its navicular facet is larger metapodials, stouter than the small species of Camelops than the cuboidal one, whereas in H. blancoensis they are (Mooser and Dalquest, 1975b). Thus we consider that the subequal in length. Compared with the astragali of Gigan- differences in some of the observed dimensions between the tocamelus or Titanotylopus, IGM 8821 is about 20% smaller specimens from San Miguel de Allende and the measurements (Meade, 1945) and is less robust. The specimen from of Webb (1965) for C. hesternus would be of similar magnitude Guanajuato is approximately 8% bigger (Voorhies and with C. traviswhitei, making it difficult to distinguish between Corner, 1986, table 2) but slender in proportion when the postcranials of the two species due to their similar size. compared with the astragali of Megatylopus? cochrani Besides, diagnostic characters of C. traviswhitei are in the (Hibbard and Riggs, 1949). The medial condyle does not dentition (Mooser and Dalquest, 1975a). overhang the sustentacular surface as in the Blancan Mega- Given the morphological similarity and close size between tylopus? species, and the navicular facet is larger than the specimens assigned to Camelops and the specimens from the cuboidal facet, while in M? cochrani, both are similar in size. Blancan of Guanajuato, the studied material is assigned to this The femur and tibia are considerably stouter and about 10% genus. At present it is not possible to assign the studied shorter than those of H. blancoensis. Compared with tibias specimens to species because the diagnostic features are in assigned to Megatylopus? cochrani, IGM 8822-2 is 10% larger crania and teeth, but it seems that the Blancan Camelops from (Voorhies and Corner, 1986, table 2) and the distal grooves are Guanajuato was not a giant camel. of unequal width, contrary to the condition observed in Megatylopus?. Compared to specimens of Blancocamelus, the This Blancan record of Camelops sp. is the first for the study tibia from San Miguel de Allende is about 16% shorter and area. considerably stouter (Meade, 1945; Dalquest, 1975). It is also MEGATYLOPUS Matthew and Cook, 1909 25% to 29% smaller and more slender than the tibias of MEGATYLOPUS sp. Gigantocamelus. On the other hand, the distal part of femur Figure 6 IGM 8822-1 is 42% narrower than that of Gigantocamelus, and the Mexican specimen is more slender. Diagnosis.—Cheek teeth more hypsodont than in Titanoty- The described material shares many characters with lopus, but much less so than in Megacamelus Frick 1929, specimens assigned to the genus Camelops, such as: the Gigantocamelus, and Camelus Linnaeus 1758; I3 and C1/c1 astragalus medial condyle does not overhang the sustentacular large and rounded, but smaller than in other Camelini except facet; the paracuboid facet is separated from the fibular facet Procamelus Leidy 1858; P1/p1 present; P3/p3 reduced; cement by a deep groove and continues dorsally to the parasustenta- lacking in molar fossettes; nasals flattened in cross section; cular facet; the navicular facet is larger than the cuboid facet limbs long without distal shortening typical of Gigantocamelus (Webb, 1965; Breyer, 1974). IGM 8821 also is similar in size to and Camelus; metapodials longer than basal length of skull specimens assigned to Camelops [astragali mean lateral length (Voorhies and Corner, 1986; Honey et al., 1998). 73 mm (Breyer, 1974, table 2)]. Description.—The DP3 of IGM 8823 is elongate and The tibia from San Miguel de Allende shares the following mesodont, slightly worn, has a triangular outline, a narrow characters with specimens assigned to Camelops: femoral anterior fossette, and a V-shaped posterior fossette. The facets of subequal length, the shaft of the tibia is anteropos- parastyle and mesostyle are prominent, and between them teriorly flattened and its anterior and posterior surfaces meet there is a slightly developed rib (Fig. 6.1, 6.2). A lingual basal on the lateral part of the shaft forming a sharp crest; on the cingulum is present. Length is 37 mm and width is 24 mm. medial side the surfaces are separated by a flat surface that The DP4 of IGM 8823 also is mesodont and slightly worn tapers distally; and the distal lateral groove is wider than the (Fig. 6.1, 6.2); the styles are prominent, and between the medial one and these grooves are separated by a prominent parastyle and mesostyle there is a narrow rib. The fossettes are crest (Webb, 1965). IGM 8822-2 is around 14% smaller than V-shaped; on the lingual side of the tooth there is a basal the least length and proximal width reported by Webb (1965, cingulum, and between both crescents there is a basal pillar. table 11), but this difference in size could be explained by Length is 40.5 mm and width is 26.4 mm. taking into account that the majority of the measurements that The fossettes of both deciduous premolars lack cement. this author made were based on Camelops hesternus (Leidy) The M1 of IGM 9326 is mesodont, has a prominent 1873, which is one of the three giant camel species within the parastyle and mesostyle, and both fossettes are V-shaped, genus (the other two are Camelops traviswhitei Mooser and deep, and lack cement; the metastyle and ribs are not developed. 60 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

In the fossettes of these teeth, the enamel of the labial side is thicker than the enamel on the lingual side. Material examined.—From locality 3467 Garbani: IGM 8823, left DP3 and DP4. From locality 3529 Tlaloc: IGM 9326, right maxillary fragment with M1 and a fragment of M2. Occurrence.—Late Clarendonian to Early Blancan and possibly Late Blancan of USA and late Hemphillian and Early Blancan or Blancan III of Mexico (Voorhies and Corner, 1986; Montellano, 1989; Honey et al., 1998). Discussion.—The DP3 of IGM 8823 was compared with UF 9197, a right DP3 from the late Hemphillian Palmetto Fauna of Florida assigned to Megatylopus gigas Matthew and Cook 1909 (Webb et al., 2008), the genotypic species of this giant camel. Both deciduous premolars have a similar morphology since the mesostyle is well developed, the parastyle is prominent and labiolingually wide, and there is a slightly developed rib between the parastyle and mesostyle (Fig. 6.1, 6.2). Also, both specimens have a basal lingual cingulum. The DP3 from San Miguel de Allende is around 15% longer than UF 91197 but only 5% wider; this could be the result of the wear stage, since the Mexican specimen is slightly worn while the one from Florida is well worn. The DP4 from San Miguel de Allende has a similar morphology and dimensions when compared with the upper molars of Megatylopus gigas. As in the molars of AMNH 14071, a skull that is the type specimen, the DP4 from the Blancan of Guanajuato has a prominent parastyle and mesostyle, an anterior rib and also a basal pillar (Matthew and Cook, 1909). It differs in the prominent metastyle that is less developed in the molars of the AMNH specimen. The DP4 from San Miguel de Allende has a lingual cingulum, weak interstylar ribs, and a well developed mesostyle, as is observed in the upper molars of the Blancan Megatylopus? cochrani. Too, it is just 4% to 7% longer than the M1 of the figured specimens of this species (Voorhies and Corner, 1986). The M1 of IGM 9326 is similar in size and morphology to the M1 of UCPM 31100, a skull from the Coffee Ranch l.f. of Texas that is the type of Megatylopus matthewi Webb 1965, the other Hemphillian species of the genus. In both, the parastyle and mesostyle are well developed, the fossettes are V-shaped, there are no ribs between the styles, and the basal cingulum is absent. The M1 from the Blancan of San Miguel de Allende also shares a prominent parastyle and the absence of ribs with the M1 of UF 134000, a tooth series with P4-M3 from the late Hemphillian Whidden Creek Fauna of Florida, assigned to Megatylopus gigas (Webb et al., 2008). The studied teeth are also close in size, style and rib development as well as fossette configuration, to upper teeth of M. matthewi from the Hemphillian of San Miguel de Allende (Jime´nez-Hidalgo and Carranza-Castan˜eda, 2005). Comparing the M1 from Guanajuanto with the M1s of M. gigas, AMNH 14071, it is observed that the tooth from Mexico lacks well-developed ribs. The basal lingual pillar, and FIGURE 6—Megatylopus sp. from the Blancan III of San Miguel de Allende, Guanajuato. IGM 8823, left DP3 and left DP4: 1, occlusal view; the fossettes are more ‘‘pinched.’’ The Guanajuato M1 is more 2, labial view. IGM 9326, right M1 and right M2 fragment: 3, occlusal brachydont than the upper molars from Nebraska, although view; 4, labial view. Scale 5 3 cm. they have a similar length and width (Matthew and Cook, 1909). The studied teeth are morphologically different to those of The labial border of both crescents is U-shaped (Fig. 6.3, 6.4). Camelops since in this genus the upper teeth have poorly The M1 is 42.5 mm in length and 33 mm in width. developed styles and ribs and are more hypsodont (Webb, The only parts that are preserved on the M2 of IGM 9326 1965). The specimens from San Miguel differ from the teeth of are the parastyle, which seems to be prominent, and a Gigantocamelus in their lesser crown height and smaller size; fragment of the anterior crescent with a U-shape outline. they also differ from those of Titanotylopus because in this JIME´NEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 61 genus the teeth are considerably larger and more brachydont (Harrison, 1985; Honey et al., 1998). Given that the studied specimens from the Blancan of San Miguel de Allende are close in morphology and size to those assigned to the genus Megatylopus, and given that they show a diagnostic feature of the genus (fossettes free of cement), the Mexican specimens are assigned to this genus. It is important to note that these teeth seem morphologically closer to those of M. matthewi than to those of M. gigas, since they are similar in size and show similar style and rib development, fossettes outline, and crown height. Voorhies and Corner (1986) also observed that the Blancan specimens of M? cochrani share more features with M. matthewi than with M. gigas. However, due to the small sample size we refrain from assigning these three teeth to any of the identified species of Megatylopus. It may be possible to determine the species as more specimens (and more tooth characters) become available. This is the first record of Megatylopus sp. in Blancan age sediments of Mexico.

PALEOBIOLOGICAL CONSIDERATIONS OF THE IDENTIFIED TAXA Biochronology.—The biochronological ranges of the five camelid species identified in the Blancan of Guanajuato are FIGURE 7—Biochronologic ranges of camelid taxa identified in the shown in Figure 7. As can be observed, Hemiauchenia Blancan I and Blancan III of San Miguel de Allende, Guanajuato, blancoensis is the species with the widest range, spanning Mexico. Solid line represents the biochronologic range observed in the study area while dashed line corresponds to taxa ranges in USA faunas. through Blancan I and Blancan III, from Chron C3n.2n to Chron C2An.1n. The record of H. blancoensis in San Miguel de Allende ly, earliest records of the four lamine camels present in the together with the one from New Mexico [Buckhorn l.f., dated Blancan of North America are in San Miguel de Allende. as 4.2–3.6 Ma (Morgan and Lucas, 2003)] are at present the The records of Hemiauchenia gracilis and Blancocamelus oldest in North America. meadei in the Blancan III of Guanajuato add to this observed The species Hemiauchenia gracilis, Blancocamelus meadei, pattern of taxa appearing earlier in southern North America. Camelops sp., and Megatylopus sp. are restricted to the Meachen (2005) points out that H. gracilis is a closer ancestor to extant llamas than any other known species; if so, Blancan III. Blancocamelus meadei and Megatylopus sp. are the South American llamas would have a Mesoamerican restricted to Chron C2An.3n (around 3.3 to 3.6 Ma), while ancestor. Camelops sp. is from C2Ar (circa 3.9 Ma) to C2An.3n, and H. Testing camelid diversification in the Mexican Pliocene is gracilis is the only species that extends from Chron C2An.3n beyond the scope of this paper, since here we are dealing with to 2An1n (at around 3.0 Ma) (Fig. 7). just a fraction of the species present during this epoch, but Again, the record of Camelops sp. in central Mexico currently we are working on it. together with those of Arizona (Bear Springs l.f.; Carnivore Paleoecology.—Previous studies of the probable feeding l.f.) and New Mexico (Buckhorn l.f.) are the oldest from strategies of fossil camelids suggest that Hemiauchenia North America, appearing at around 3.6–4.0 Ma (Honey et blancoensis was a browser-like intermediate feeder or even a al., 1998; Morgan and Lucas, 2003; Morgan and White, 2005; browser, that H. gracilis was mainly a browser with a small White and Morgan, 2005). amount of grass in its diet, while Camelops was a mixed-feeder By the same token, the biochronologic range of Mega- and Megatylopus was a browser or high-level browser tylopus sp. is within that reported from other localities in (Voorhies and Corner, 1986; Dompierre and Churcher, 1996; North America (Honey et al., 1998), but the lamines H. MacFadden and Cerling, 1996; Feranec, 2003; Meachen, gracilis and Blancocamelus meadei appear around 500 ka 2005); by the same token, the extremely long limbs of earlier in San Miguel de Allende (Blancan III) than in the USA Blancocamelus meadei suggest that it probably was a high- faunas, where their appearance is in the Blancan V [or the Late level browser, as is inferred for Aepycamelus MacDo- Blancan (Honey et al., 1998; Meachen, 2005)]. nald,1956. So these species had similar feeding strategies. The earlier appearance of several mammalian taxa in the In order to establish the body mass distribution of the faunas of central and southern Mexico when compared with identified species in this study, we estimated the probable body those of USA is a common pattern observed during the mass of some specimens using the predictive equations of Janis Neogene (Jimeńez-Hidalgo et al., 2004; Montellano-Balles- (1990) for the m1–m3 length (her LMRL) for ruminants, those teros and Jimeńez Hidalgo, 2006; Woodburne et al., 2006; of Scott (1990), for ruminants according to the postcranial Wang and Carranza-Castan˜eda, 2008). It has been proposed element available (F5, MT2, T2) and that of algorithm 7.1 of that this pattern suggests that species diversification within lower teeth of Mendoza et al. (2006); we also took previous several mammalian lineages took place in Mexico during the estimations from literature. When available we utilized the Miocene and Pliocene (Jimeńez-Hidalgo et al., 2002; Ferrus- measurements of the San Miguel de Allende specimens, or if quıá-Villafranca, 2003; Woodburne et al., 2006; Bravo-Cuevas not, we used those from specimens assigned to the same and Ferrusquıá-Villafranca, 2008; among others); interesting- species from the literature. In the case of Megatylopus sp., we 62 JOURNAL OF PALEONTOLOGY, V. 84, NO. 1, 2010

TABLE 8—Estimated body masses (in Kg) of the camelids from the Blancan of San Miguel de Allende. * Value estimated with Algorithm 7.1 of Mendoza et al. (2006).

Species Measured specimen Janis (1990) Mendoza et al. (2006) Scott (1990) Reported from literature Hemiauchenia blancoensis . IGM 2346 380.0 324.0 .. Hemiauchenia gracilis . UF 210707 195.0 599.0* . . UF 45275 205.0 Blancocamelus meadei . TMM 6421 .. 1,438.0 . Camelops sp. . IGM 8822-2 .. 599.0 . Megatylopus sp. .... 589–1,259 took its possible body mass from Scott (1990, table 14.6) and Camelops sp. represents 9.3% of NISP and 6.9% MNI, and the Lambert (2006, appendix 8). Estimated body masses are cameline Megatylopus is represented by 6.2% of NISP and presented in Table 8. As expected for the giant camels 6.9% of MNI. Blancocamelus and Megatylopus, they show the highest body Geographic distribution.—During the Early Blancan, Hemi- mass values, followed by Camelops and H. blancoensis, while auchenia blancoensis, Camelops sp. and Megatylopus sp. were the small H. gracilis has the lowest body mass. Regarding this widely distributed in North America; there are records of these last species, the equation of algorithm 7.1 of Mendoza et al. taxa in the Pacific Northwest, the Central and Southern Plains (2006) gave an aberrant estimation of 599 kg, even higher than (Janis et al., 1998) and to the south in central Mexico (Fig. 8). the one of Camelops and within the range estimated for Their geographic distribution covers a latitudinal gradient of Megatylopus (Table 8). Thus, we calculated an additional around 26u, from roughly 47u Lat. N to 21u Lat. N, and body mass using the area of m2 (SLMA of Janis, 1990), giving longitudinally about 24u, from western to central USA (123u 191 kg. We consider that H. gracilis has an estimated body Long. W to 99u Long. W). Such a pattern indicates that H. mass of around 200 kg and discard the anomalous value of blancoensis, Camelops sp. and Megatylopus sp. were successful 599 kg. taxa that roamed in different habitats through large part of It is evident that the five identified species show a diversity North America, excepting the eastern part of USA. The two of body masses, which probably prevented competition for lamine genera Hemiauchenia and Camelops retained this wide feeding resources, given that body mass is intimately geographic distribution until the Late Pleistocene, with correlated with life history of taxa and the species of plants records from southern Canada and northwestern USA to on which an herbivore can feed efficiently (Eisenberg, 1990; central Mexico (Faunmap Working Group, 1994; Jime´nez- Maiorana, 1990). Hidalgo and Guerrero-Arenas, 2006); recently, paleontologi- In the sample from San Miguel de Allende, 68.7% of the cal fieldwork carried out in Rancholabrean fluvial sediments number of identified specimens (NISP) and 72.4% of the of northwestern Oaxaca, southern Mexico, allowed us to recover some Camelops teeth that are now under study, minimum number of individuals (MNI) belong to Hemi- increasing its geographic distribution farther south during the auchenia blancoensis, representing the most common camel in Late Pleistocene. the area. Meanwhile H. gracilis is the second most common, On the other hand, the records of Blancocamelus meadei and with 12.5% of NISP and 10.3% of MNI. Blancocamelus Hemiauchenia gracilis during the Blancan indicate a geograph- meadei is the rarest with 3.1% of NISP and 3.4% of MNI, ic distribution primarily in central and southern North America (Fig. 9), whereas Blancocamelus is present in the

FIGURE 8—North American localities of early Blancan age with records of Hemiauchenia blancoensis (square), Camelops sp. (circle) and Mega- FIGURE 9—North American localities of Blancan age with records of tylopus sp. (asterisk). Blancocamelus meadei (circle) and Hemiauchenia gracilis (square). JIME´NEZ-HIDALGO AND CARRANZA-CASTAN˜ EDA—BLANCAN CAMELIDS FROM CENTRAL MEXICO 63

Southern Plains, Southern Basin and California Coast (Janis and Cenozoic mammals of North America: Biostratigraphy and et al., 1998), and H. gracilis is on the Gulf Coast and as far Geochronology. Columbia University Press, New York. BRAVO-CUEVAS, V. AND I. FERRUSQUIÁ-VILLAFRANCA. 2008. Cormohip- west as Arizona and New Mexico (Meachen, 2005; White and parion (Mammalia, Perissodactyla, Equidae) from the middle Miocene Morgan, 2005). The older records of both species are in of Oaxaca, southeastern Mexico. Journal of Vertebrate Paleontology, subtropical North America, in the Blancan III of San Miguel 28:243–250. de Allende. BREYER, J. A. 1974. Examination of selected postcranial elements in Pleistocene camelids. Contributions to Geology, 13:75–85. The records of these five camelid taxa in the Early Blancan BREYER, J. A. 1977. Intra- and interespecific variation in the lower jaw of of San Miguel de Allende are at present the southernmost in Hemiauchenia. Journal of Paleontology, 51:527–535. North America during the Pliocene. BREYER, J. A. 1983. The biostratigraphic utility of camel metapodials. Journal of Paleontology, 57:302–307. CONCLUSIONS CARRANZA-CASTAN˜ EDA, O. 2006. Late Tertiary fossil localities in central Mexico, between 19u–23u N, p. 45–60. In O. Carranza-Castan˜eda and E. The fossil record of Pliocene camelids from Mexico is H. Lindsay (eds.), Advances in late Tertiary vertebrate paleontology in scattered and poorly known. Mexico and the Great American Biotic Interchange. Universidad In the San Miguel de Allende area, Guanajuato, we Nacional Autońoma de Me´xico, Instituto de Geologıá and Centro de identified four of the six camelid genera present in the USA Geociencias. Publicacioń Especial 4. CARRANZA-CASTAN˜ EDA, O. AND W. E. MILLER. 1998. Paleofaunas de faunas during the Blancan mammal age. 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