Protitan grangeri ( Osborn, 1925 )

Mihlbachler, Matthew C., 2008, Species Taxonomy, Phylogeny, and Biogeography of the Brontotheriidae (Mammalia: Perissodactyla), Bulletin of the American Museum of Natural History 311 (1), pp. 1-475 : 141-152

Protitan grangeri ( Osborn, 1925)

HOLOTYPE: AMNH 20103 , a complete skull and mandible.

TYPE LOCALITY: Irdin Manha Formation, one half mile south of the Kalgan Urga telegraph line, Inner Mongolia, China.

AGE: Middle Eocene (Irdinmanhan land mammal ‘‘age’’).

SYNONYMS: Dolichorhinus olseni Osborn, 1925 ; ‘‘ Manteoceras ?’’ irdinensis Osborn, 1925; Protitan robustus Granger and Gregory, 1943 ; Protitan bellus Granger and Gregory, 1943 ; Protitan obliquidens Granger and Gregory, 1943 .

REFERRED SPECIMENS: (From the Irdin Manha Formation, Inner Mongolia) AMNH 19179 , a mandible fragment with left p2 (partial), p3–m2, and m3 (partial) ; AMNH 20104 (holotype of Protitan robustus ), a partial mandible with right i1–c, p2–p3, and left i1–m3 ; AMNH 20108 , a right maxilla with P1–M3 ; AMNH 20109 (holotype of Dolichorhinus olseni ), a mandible with right i3, p1–m3, and left c–m3 ; AMNH 20111 (holotype of ‘‘ Manteoceras ?’’ irdinensis), a mandible fragment with right m1–m3 ; AMNH 20112 , a partial mandible with i2–c and p2–m3 ; AMNH 20113 , an anterior portion of a cranium with right C, P2–P4, and M1 (partial) ; AMNH 20114 , an anterior portion of a cranium with right I2–M1, left C, and P2–M3 ; AMNH 20119 , a mandible fragment with right p4–m2 ; AMNH 20120 , a right maxilla fragment with M1–M3 ; AMNH 20123 , a left maxilla fragment with P4–M2 ; AMNH 20125 (holotype of Protitan obliquidens ), a left maxilla fragment with P1–P3 ; AMNH 20126 , a mandible fragment with left p3–m2; (from the Ulan Shireh Formation of Inner Mongolia) AMNH 26104 (holotype of Protitan bellus ), a ventral surface of a cranium with right and left I2–M3; (from the?‘‘ Houldjin’ ’ beds at Camp Margetts ) AMNH 26421 , a mandible with some intact incisors, right p2–m3, and left p1–m3 .

DIAGNOSIS: Protitan grangeri is a large brontothere with small but distinct elliptical frontonasal horns positioned low on the skull and far in front of the orbit. The nasal incision is dorsoventrally shallow and extends posteriorly to the P3. The nasal process is slightly angled downward, unelevated, long and broad, with thickened sides, and with a thin and strongly rounded distal edge with a downturned distal tip. The orbits are positioned above the posterior portion of M2 and the anterior portion of M3. The premaxillomaxillary rostrum deepens posteriorly and it is not enclosed by bone dorsally. Other cranial characteristics include a saddle-shaped cranium, separate parasagittal ridges that strongly constrict the dorsal width of the cranium posteriorly, postzygomatic processes, large ventral sphenoidal fossae, nearly straight zygomatic arches, and a ventrally unconstricted and mediolaterally angled external auditory pseudomeatus.

Dentally, Protitan grangeri has three large to intermediate-sized subcaniniform upper incisors, a simple P1, and a distinct P2 metacone. Premolar hypocones are absent, although a short crest usually extends from the protocones. The molars of P. grangeri have tall, lingually angled ectolophs with weak labial ribs, and thinned lingual ectoloph enamel with wedge-shaped paracones and metacones. A cingular parastyle shelf is absent. Very shallow central molar fossae are present. Anterolingual cingular cusps are absent. Paraconules and metalophs are absent. The lower dentition of P. grangeri includes three large incisors, a semispatulate i1 and i2, and a more subcaniniform i3. Additional lower dental characters include, a distinct postcanine diastema, a metaconid on p4 but not on p2 or p3, shallow molar basins, and a slender m3.

Protitan grangeri closely resembles Protitanotherium emarginatum and Protitan minor . It can be most easily distinguished from Protitanotherium by the larger more subcaniniform incisors, a ventrally unconstricted external auditory pseudomeatus, and postzygomatic processes. Protitan grangeri can be distinguished from Protitan minor by its anteroposteriorly shorter nasal incision, thicker nasal, more anteriorly positioned horns, and mediolaterally angled auditory pseudomeatus.

DESCRIPTION

SKULL: The holotype of Protitan grangeri (AMNH 20103) is a complete and relatively undistorted skull (figs. 66, 67) and jaw (fig. 68) with a complete set of dentition, but with rather poorly preserved cheek teeth. No other complete skulls of P. grangeri are known, although there are several additional partial crania, including AMNH 26104, a complete ventral surface, and several anterior portions of skulls including AMNH 20108, AMNH 20114, and AMNH 20113. The following description of P. grangeri is based primarily on AMNH 20103, but additional

(C) oblique view, (D) anterior view, (E) posterior view.

information is taken from these other specimens where noted.

Protitan grangeri is a large (table 9) brontothere with an elongate cranium and small but conspicuous frontonasal protuberances that are similar in size to those of Protitan minor and Protitanotherium emarginatum . From the right side of the skull the frontal bone can clearly be seen overlapping the nasal bone and extending to the peak of the horn. The horns of AMNH 20103 are short and elliptical in shape with a longer anteroposterior axis. The peaks of the horns lack distinct rugosities, and the surfaces of the horns are no rougher than the remaining surface of the skull. The horns project dorsolaterally from the sides of the skull and they are widely separated by a broad and flat forehead. The horns are positioned low on the skull although they are much further anterior to the orbits in comparison to those of Protitan minor and Protitanotherium emarginatum .

Like Protitan minor and Protitanotherium emarginatum , the nasal incision is dorsoventrally shallow. However, it is anteroposteriorly shorter than in other taxa. The nasal incision extends posteriorly to the P3 and the orbit is positioned over the anterior portion of M3 and the posterior portion of M2. The anterolateral root of M2 rests below the anterior rim of the orbit.

From the lateral view of the skull the nasal process of the holotype curves downward anteriorly and is the same length as the premaxillomaxillary rostrum. The sides of the nasal process are thickened, rounded, and angled downward. The sides are not up-

TABLE 9 Summary statistics for selected morphometric variables of Protitan grangeri See Methods for measurement definitions turned as are the nasals of Diplacodon elatus . Thin, vertical lateral walls, such as those seen in Epimanteoceras formosus and other hornless brontotheres, are not seen in Protitan grangeri . From a dorsal view of the skull it can be seen that the nasal bones are strongly fused together. The nasal process is wide, about the same width as the premaxillomaxillary rostrum. Throughout its length the nasal process is nearly constant in width. The distal edge of the nasal process is strongly rounded although there is a slight anterior notch at the midline. From the lateral and anterior views of the skull it can be seen that the anterior end of the nasal process is thinned and strongly curved downward. The anterior edge of the nasal process is thin and irregular.

From the lateral view of the holotype skull, the dorsolateral margin of the premaxillomaxillary rostrum rises posteriorly at a shallow angle so that the posterior notch of the nasal incision is at the level of the upper rim of the orbit. The premaxillae contact each other medially at the premaxillomaxillary symphysis although the symphysis is not completely fused. The premaxillomaxillary suture can be seen in AMNH 20103 most clearly from the oblique view of the skull. The premaxilla is truncated before reaching the posterior notch of the nasal incision, thus, the premaxilla does not contact the nasal bone. The dorsolateral margins of the premaxillae diverge posterolaterally and the rostral cavity is dorsally open.

From the lateral view the dorsal surface of the skull is fully concave from the orbits to the nuchal crest, forming a completely saddle-shaped cranium. The parasagittal ridges remain separate and do not form a sagittal crest although they strongly constrict the dorsal surface of the cranium posteriorly. The zygomatic arches are rather shallow dorsoventrally and have a narrow rectangular cross section. The zygomatic arches of AMNH 26104 are somewhat thicker and more robust than those of AMNH 20103, but they are otherwise similar. The zygomatic arch is essentially uncurved from a lateral view. From a dorsal view the zygomatic arches are bowed slightly inward. However, the zygomatic arches of AMNH 20103 are composed of several fragments that have been bonded together with plaster and it is probable that the inwardly bowed shape is an artifact of distortion and subsequent reconstruction of the fossil. Unlike the holotype, the zygomatic arches of AMNH 26104 are not inwardly bowed. Discounting the slight inward bowing of the zygomatics of the holotype, the zygomatic arches appear to have been straight and strongly angled posterolaterally. The posterodorsal end of each of the zygomatic arches exhibits a small dorsally projecting process that was referred to by Granger and Gregory (1943) as a ‘‘postzygomatic horn’’ ( Granger and Gregory, 1943: 359). One of these postzygomatic processes can most easily be seen on the right side of the skull (fig. 66).

From the lateral view of the skull the occiput is moderately angled backward. From the dorsal view the nuchal crest is nearly flat. From the posterior view the dorsal rim of the occiput is dorsally arched. The dorsal portion of the occiput is slightly narrower than the ventral portion of the occiput and the occiput is strongly constrict- ed in the middle. Weak occipital pillars are evident on the posterior surface of the occiput, although the central depression of the occiput is rather shallow.

From the ventral view of AMNH 20103 (fig. 67a) the anterior rim of the posterior nares is situated slightly behind the M3 protocones. The narial canal is rimmed by a rather wide U-shaped emargination. In both the holotype specimen and the other complete ventral skull surface (AMNH 26104), the elongate posterior canal is filled with plaster. In AMNH 20103 roughly the posterior half of the elongate posterior narial canal is free of plaster. In that specimen the canal extends significantly into the basisphenoid. The ventral sphenoidal fossae are rather large, but they are shallow. These were called presphenoid pits by Osborn (1925, 1929a) and were called basisphenoid pits by Granger and Gregory (1943). A remnant of the thin bony septum formed by the main body of the sphenoid that partitions the ventral sphenoidal fossae is still preserved in position.

Other aspects of the basicranium of AMNH 20103 and AMNH 26104 are rather typical, such as the widely separated foramen ovale and foramen lacerum. The occiput and basicranium are not disproportionately widened as those of Rhinotitan andrewsi or Metatitan . The external auditory pseudomeatus is directed mediolaterally. From the lateral view the external auditory pseudomeatus is wide and open ventrally.

UPPER DENTITION: The holotype of Protitan grangeri (AMNH 26103) retains a complete dentition (fig. 67a). Although the incisors of the holotype are in good condition (fig. 67d–e), the cheek teeth are poorly preserved. However, AMNH 26104 has a nearly complete set of upper dentition whose cheek teeth are significantly less worn and less damaged than those of AMNH 26103. Therefore, the cheek teeth of AMNH 26104 are shown in close-up (fig. 67b, c).

Protitan grangeri retains an unreduced dental formula (3-1-4-3). The incisors and canines of the holotype are relatively small, though by no means are they as reduced as those of Protitanotherium emarginatum . The anterior dentitions of other specimens referred to Protitan grangeri are larger. For instance, the incisors and canines of AMNH 26104 are distinctly larger than those of AMNH 20103. However, the premaxillae of both specimens are of similar size; in AMNH 20103 there are small diastemata between the incisors, whereas in AMNH 26104 there are no diastemata between the incisors (except for a median diastema). Osborn (1929a) attributed the smaller size of the incisors of AMNH 20103 to sexual dimorphism. Variation in incisor and canine size seen here and in other brontotheres such as Aktautitan hippopotamopus and Gnathotitan berkeyi probably represents sexual dimorphism.

The incisors of Protitan grangeri form an arched row anterior to the canines. They increase in size laterally and retain plesiomorphic subcaniniform morphology with short but conical and lingually curved crowns with distinct lingual cingula. Labial incisor cingula are absent. The canine of AMNH 20103 is small while that of AMNH 26104 is larger, even though it is otherwise morphologically similar. There is both a short precanine diastema and a longer postcanine diastema. The postcanine diastema of AMNH 26104 seems proportionally shorter but this difference can largely be attributed to the larger canine.

The P1 is a single-cusped tooth with an elongate posterior heel. The anterior margin of P2 is angled posterolingually, giving the tooth a somewhat oblique shape. The anterior and posterior margins of P3 and P4 are more nearly parallel. The parastyle and metastyle of P2 arch somewhat lingually. The parastyle and metastyle of P3 are nearly straight. The parastyle of P4 is slightly angled lingually while the metastyle is more nearly straight. The labial margin of the P2 protocone is very convex, while the paracones of P3 and P4 have distinct labial ribs. Finally, the metacone of P2 is lingually shifted, while those of P3 and P4 are more labially positioned. As a consequence, the ectoloph of P2 is rounder than those of P3 and P4.

The lingual features of the premolars have a relatively low level of topographic relief and they exhibit considerable intraspecific variation. On the P2 of the holotype specimen (AMNH 20103) there is a distinct protocone followed by a short lingual crest. However, in AMNH 26104 a single loph of enamel stretches around the anterolingual side of the P2 crown and although there are no distinct lingual cusps. The P2s of AMNH 20103 and AMNH 26104 have small preprotocristae. A less distinct preprotocrista is seen on the P3 of the holotype and it is absent on the P3 of AMNH 26104. The P3 protocones are followed by short lingual crests on both specimens. A preprotocrista is not seen on the P4 of either specimen. A lingual crest is not seen on the P4 of the holotype, but a short lingual crest is present on the P4 of AMNH 26104. A few specimens have small paraconules on the P2–P4 but these are most often absent. Premolar hypocones are nearly always absent in P. grangeri , though one specimen, AMNH 20123, has a very small hypocone positioned close to the protocone of the P4. Labial premolar cingula are weak. The anterior and posterior premolar cingula wrap around the lingual sides of the crowns and join to form continuous lingual cingula. Among all of the available specimens, the lingual premolar cingula range from continuous around the protocone to slightly discontinuous.

The upper molars of Protitan grangeri show numerous brontotheriine apomorphies, including tall, lingually angled ectolophs, very weak labial ribs, thin lingual ectoloph enamel, and wedge-shaped lingual sides of the paracone and metacone in molars that are not heavily worn. The anterior cingulum is thin and passes proximally to the distal peak of the parastyle. Shallow central molar fossae are present but anterolingual cingular cusps are absent. All evidence of paraconules and metalophs is lost. There is no trace of a hypocone on any M3 of P. grangeri . Labial molar cingula are weak and lingual molar cingula are absent.

MANDIBLE AND LOWER DENTITION:

The holotype mandible (AMNH 20103) is missing only the condyles and coronoid processes (fig. 68). The lower dentition of the holotype is complete, but cheek teeth are poorly preserved. However, the lower dentition of a referred specimen (AMNH 20104) is complete, similar to that of the holotype, and in more pristine condition. Therefore, the lower teeth of this specimen are figured in close-up (fig. 69).

The coronoid process of AMNH 20104 is tall, slender, and moderately curved. The mandibular symphysis is long and narrow in AMNH 20103, although it is somewhat more robust in AMNH 20104. The angle of the ventral margin of the symphysis of AMNH 20103 is shallow (, 45 °). However, as noted by Granger and Gregory (1943), the shallow orientation of the symphysis seems to have been influenced by taphonomic distortion. A segment of the right ramus below the p3 is reconstructed with plaster, suggesting that the anterior portion of the mandible has been forced or rotated downward. The anterior portion of AMNH 20104 is more intact and suggests a steeper mandibular symphysis. The exact posterior edge of the symphysis is obscured by plaster in AMNH 20103, but in AMNH 20104, the symphysis extends posteriorly to the talonid of the p3.

The lower incisors are relatively large and they form an arched row anterior to the canines. In the holotype the crowns of i1 and i2 are significantly worn, but those of AMNH 20104 are nearly unworn. The crowns of i1 and i2 are generally semispatulate with rounded apices, while i3 has a more sharply defined apex. There are distinct lingual cingulids on i1–i3. Labial cingulids are not seen. The i3 is mesiodistally elongate in comparison to i1 or i2. Each incisor is roughly of similar size. The lower canines of AMNH 20103 are notably smaller than those of AMNH 20104. The length of the lower postcanine diastema, the only diastema of the lower dentition, covaries with canine size. In AMNH 20103 the postcanine diastema is about double the length of the p2 whereas in AMNH 20104 the postcanine diastema is

(C) dorsal view, (D) lingual view of incisors and canines, (E) labial view of incisors and canines.

shorter, corresponding to the larger size of the canines.

The lower premolars are low crowned and relatively slender. The p1 is a very small tooth with a single cusp and a short talonid heel. The trigonid of p2 is much longer than the talonid. The p3 trigonid is somewhat longer than the talonid, while the p4 trigonid is similar in length to the talonid. The trigonid and talonid of p2 are of similar width, while the p3 and p4 trigonids are slightly narrower than their talonids. The p2 paralophid barely arches lingually and there is only a minor lingual trigonid notch. The p2 protolophid extends in a posterior direction, but it is positioned lingually. The p3 paralophid arches slightly lingually, creating a more distinct lingual trigonid notch. The p3 protolophid is moderately angled lingually. Metaconids are absent on p2 and p3. The trigonid of p4 is more molariform with a strongly lingually arching paralophid and protolophid and a large lingually positioned metaconid. The talonid of p2 is very small, with a very short cristid obliqua and hypolophid. The lingual face of the p2 talonid is a flat and sloped surface. The cristids obliqua and hypolophids of p3 and p4 are progressively longer although the lingual face of p3 forms only a broad concave surface. Howev- er, the talonid of p4 has a nearly molariform talonid basin. Labial and lingual premolar cingulids are essentially absent although a very faint labial cingulid can be seen on p4.

The lower molars of Protitan grangeri are typical with relatively thin lingual enamel, shallow trigonid and talonid basins, and an elongate m3. There are no lingual cingulids. Labial molar cingulids are distinct although they tend to be discontinuous around the paraconids and metaconids.

REMARKS

Protitan grangeri ( Osborn, 1925) is based on a complete skull and jaw (AMNH 20103). Osborn (1925) originally referred this species to the genus Protitanotherium , based on the ‘‘elongate horns’’, the ‘‘broad shovel-shaped nasals’’, the ‘‘saddle-shaped cranial top’’, and several other minor details. Several other species have been referred to Protitan , although most of these turn out to be invalid synonyms and nomina dubia. Osborn named two other Asian brontothere species, Dolichorhinus olseni Osborn (1925) and ‘‘ Manteoceras ?’’ irdinensis Osborn (1925). In their revision of Mongolian brontotheres, Granger and Gregory (1943) erected a new genus, Protitan , with P. grangeri serving as the type species. In addition to Protitan grangeri, Granger and Gregory (1943) named five other species of Protitan , including P. minor , P. robustus , P. bellus , P. obliquidens , and ‘‘ Protitan ?’’ cingulatus . They considered Dolichorhinus olseni Osborn (1925) and ‘‘ Manteoceras ?’’ irdinensis Osborn (1925) to be synonyms of Protitan grangeri .

Among these species, Protitan minor is the only other species previously referred to Protitan that may actually belong to this genus, although even its membership is questionable (see remarks under Protitan minor ). ‘‘ Protitan ?’’ cingulatus is a dubious species that may actually be synonymous with Epimanteoceras formosus . The remaining species, Dolichorhinus olseni , ‘‘ Manteoceras ?’’ irdinensis, P. robustus , P. bellus , and P. obliquidens are junior synonyms of P. grangeri .

Dolichorhinus olseni was based on a complete mandible (AMNH 20109) lacking most of its anterior dentition. It is not clear why Osborn (1925, 1929a) assigned this species to Dolichorhinus . Osborn did not attempt to differentiate Dolichorhinus olseni from Protitan grangeri , despite that fact that these taxa are based on very similar fossil material. Granger and Gregory (1943) considered D. olseni to be a junior synonym of P. grangeri , but they noted that the m3 was slightly shorter than on the holotype of P. grangeri (AMNH 20103).

‘‘ Manteoceras ?’’ irdinensis is based on a partial ramus with m1–m3 that is reconstructed in such a way that suggests a very short space for a premolar row and a very short and flattened symphysis. All these features are relevant to Osborn’s (1925) diagnosis, which includes an apparently reduced number of premolars (judging by the premolar alveoli), unusually procumbent incisors (judged by the angle of the symphysis), and a short symphysis. The short symphysis is artificial and related to the fact that the anterior end is missing. Additionally, the ramus has been incorrectly reconstructed; the symphysis is plastered directly to the horizontal ramus, although a segment of the horizontal ramus appears to be missing, thus giving the artificial appearance of a shortened jaw. Likewise, the shallow angle of the symphysis and, hence, the procumbent nature of the incisor alveoli are simply a result of how the specimen has been reconstructed. The molar measurements of this specimen are similar to Protitan grangeri . Thus, ‘‘ Manteoceras ?’’ irdinensis is considered a junior synonym of P. grangeri .

Granger and Gregory (1943) based Protitan robustus on a partial mandible with complete and lightly worn dentition (AMNH 20104). This species was diagnosed on the following criteria: (1) size large (presumably in comparison to P. grangeri ), (2) incisors large, wide spreading, (3) canines very massive with recurved crowns, and (4) ‘‘postcanine diastema short’’. However, none of these observations clearly differentiates P. robustus from Protitan grangeri . AMNH 20104 is larger than the holotype of P. grangeri (AMNH 20103), but the difference is not extreme and this specimen easily fits into an acceptable size range for P. grangeri (table 9). Granger and Gregory (1943) actually noted that the dentition of AMNH 20104 nearly fit onto AMNH 26104 (holotype of P. bellus , a synonym of P. grangeri ; see next paragraph), but they even rejected the possibility that these two specimens are the same species because the match was not perfect! (Intraspecific variation and taphonomic distortion were largely ignored by Granger and Gregory [1943].) In comparing AMNH 20104 with the holotype mandible (AMNH 20103) of P. grangeri , the larger size of the incisors and canines of the former is consistent with sexual dimorphism. Likewise, the shorter postcanine diastema can be explained by the fact that the canine root of AMNH 20104 is much larger and takes up more space. Nothing else appears to differentiate this specimen from P. grangeri .

Protitan bellus was based on a ventral surface of a skull with a nearly complete set of upper dentition (AMNH 26104). Granger and Gregory (1943) distinguished P. bellus from P. grangeri with the following diagnosis: (1) upper molars anteroposteriorly longer than in P. grangeri , especially M1. (2) P3 with incipient tetartocone (5 hypocone) swelling, (3) P4 more elongate, (4) incisors much larger than in the type of P. grangeri , and (5) width across opposite M3 distinctly larger. Observations 1, 3, and 5 were based on ratios in which AMNH 26104 differs slightly from AMNH 20103 (See table 5 of Granger and Gregory, 1943). However, either these differences can be attributed to the more damaged and more heavily worn state of the dentition of AMNH 20103 compared with that of AMNH 26104 (observations 1 and 3), or the differences are so small (4 %) that they do not warrant a taxonomic distinction (observation 5). While I could not confirm the presence of an ‘‘incipient hypocone’’ on the P3 of AMNH 26104 (observation 2), there are small lingual crests on the P3 and P4. These are not present in the holotype of Protitan grangeri ; however, this character is strongly variable in most brontothere species. Moreover, other specimens that Granger and Gregory (1943) referred to P. grangeri show similar variations in premolar morphology. Therefore, AMNH 26104 does not really stand out in this respect. Clear differences between AMNH 20103 and AMNH 26104 include the large incisors and canines (observation 4 of Granger and Gregory [1943]), larger size, and thicker zygomatic processes. These character differences are most consistent with sexual dimorphism. AMNH 26104 is marginally larger than the holotype of P. grangeri .

The obliqueness of the premolars (P2–P3) of a maxillary fragment (AMNH 20125) led Granger and Gregory (1943) to assign it to yet another a new species, Protitan obliquidens . Granger and Gregory (1943) remark in their diagnosis: crown pattern of P2, P3 very oblique both on the anterointernal and posteroexternal. However, this specimen does not really stand out in comparison to other specimens of Protitan . In particular, the P2 of all Protitan specimens is oblique in appearance, although the extent of obliqueness is somewhat variable. As Granger and Gregory (1943) note, the shape of the premolars closely resembles those of AMNH 26104 except in the much greater maximum oblique width of P2. However, the difference in the shape of the P2 of AMNH 20125 is subtle and the P2 and P3 are cracked in numerous places with bits of matrix and plaster between the spaces; the teeth of this specimen are clearly distorted to a minor degree. The minor differences in the apparent degrees of obliqueness of these teeth can largely be attributed to this distortion. Realistically, the molar dimensions of AMNH 20109 are similar to those of Protitan grangeri and this specimen is likely to represent the same species.

Subsequent to Granger and Gregory’s (1943) publication, paleontologists working with Asian brontothere material have shown a mistaken tendency to assign large middle Eocene brontothere fossils to the genus Protitan , although their use of Protitan has been far too broad; none of the material outside of the original AMNH central Asiatic expedition collection resembles the species referred to Protitan by Granger and Gregory (1943). Two species named by Yanovskaya (1980), P. khaitshinus and P. reshetovi , are actually Metatitan . Yanovskaya (1980) incorrectly reassigned Protitan robustus to the genus Epimanteoceras and wrongly synonomized it with Epimanteoceras amplus (a dubious species that is, nonetheless, very different from Protitan and might be a synonym of Nasamplus progressus ). None of the material described in Yanovskaya’s (1980) monograph on Mongolian brontotheres appears to belong to any species of Protitan . Qi et al. (1992) referred another specimen (IVPP–V10104, presumed to represent a single individual) from the Tukhum beds of Erden Obo (Urtyn Obo) to Protitan sp. The material includes an elongate m3 and an assortment of postcranial elements. Although the size of the m3 is consistent with P. grangeri , it lacks diagnostic characters and could belong to one of a number of brontotheres including Epimanteoceras , Metatitan , or others. Preliminary reports of a brontothere from the Ily Basin of Kazakstan were referred to Protitan ( Emry et al., 1997; Emry and Lucas, 2002, 2003; Lucas and Emry, 2001), although this brontothere turned out to be a new genus and species, Aktautitan hippopotamopus ( Mihlbachler et al., 2004a) . Most recently, Huang and Zheng (2004) named a new species, Protitan major , from the Lumeiyi Formation of China, although the material assigned to this species represents a brontothere with much more advanced dentition and it possibly belongs to Metatitan . Other material from the Lumeiyi formation assigned to Protitan cf. P. robustus by Zheng et al. (1978) and Huang and Zheng (2004) lack sufficient diagnostic characters for species or genus identification.