Eotitanops borealis Cope 1880

Species Eotitanops borealis (Cope 1880) = E. brownianus (Cope 1881) = E. princeps Osborn 1913 = E. major Osborn 1913? Holotype: AMNH 4892, a right maxilla with complete P 4 to M 1 and fragmentary M 2 to M 3. Referred specimens: AMNH 296 (type of E. princeps), AMNH 4885 (type of E. brownianus), AMNH 14887 (Osborn's " neotype " of E. borealis), AMNH 14888, AMNH 14890, and AMNH 14891. Diagnosis: Large species of Eotitanops distinguished from E. gregoryi by its much larger size and lack of an entoconid on p 4. Discussion: Although many specimens were referred to Eotitanops borealis by Wallace (1980), the list of referred specimens in the present paper is limited to the type, Osborn's " neotype " skull of E. borealis, and the specimens that were used in the statistical analysis discussed above.Published as part of Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), pp. 1-43 in Zootaxa 2339 on page 14, DOI: 10.5281/zenodo.19327

Palaeosyops Leidy 1870

Genus PALAEOSYOPS Leidy 1870 = Limnohyus Marsh 1872 = Limnohyops Marsh 1890 = Eometarhinus Osborn 1919 Age: Bridgerian. Subage: Gardnerbuttean, Blacksforkian, and Twinbuttean. Type species: P. paludosus Leidy 1870. Included species: P. fontinalis (Cope 1873 a); P. robustus (Marsh 1872). Diagnosis: Medium-sized (length P 2 to M 3 approximately 123 to 165 mm) brontothere with six upper and lower incisors; large canines; very small or no upper diastema and a moderate lower diastema (mostly between p 1 and p 2); unmolarized premolars; large paraconules on the molars; hypocone or pseudohypocone variably present on M 3. Palaeosyops is distinguished from all other brontotheres by the following synapomorphies: strongly brachycephalic skull; robust zygomatic arches that are sharply curved; sharply curved nasals that taper distally; and a low convexity or dome in the region of the frontoparietal border (see Figure 6). Discussion: Leidy based the type species of Palaeosyops, P. paludosus, on four isolated teeth collected from Church Buttes in the Green River Basin of Wyoming (Leidy 1870). Of these cotypes, Osborn (1929) selected USNM 759, a lower second molar, as the lectotype for the type species. Based on the length and width of the lectotype molar, Mader (1989) concluded that the type belongs to the same taxon as the medium-sized, brachycephalic brontotheres later named Limnohyus and Limnohyops by Marsh (see Figure 6). Because the lectotype appeared to be identifiable, Mader accepted the name Palaeosyops as valid, but noted that if the lectotype should prove to be inadequate for diagnostic purposes, the next available name would be Limnohyus Marsh (1872; type species L. robustus), which is based on a relatively complete skull (YPM 11122). The lectotype of Palaeosyops paludosus is from the Blacks Fork Member of the Bridger Formation, and because only one brontothere genus has been reliably recorded from this level, it is almost certain that Palaeosyops is a valid taxon. Within two years after Leidy's naming of Palaeosyops paludosus, Marsh recognized that some of the specimens that had been referred to Palaeosyops had a hypocone on the M 3 and some did not. Marsh (1872) proposed that the name Palaeosyops be restricted to those animals with a hypocone and that the name Limnohyus be given to those without it. Leidy (1872 b), however, pointed out that the absence of a hypocone was a character originally attributed to Palaeosyops (the type series of Palaeosyops paludosus included an M 3 that lacked a hypocone) and could not be used to define a new genus. Marsh later (1890) reversed his previous position and applied the name Palaeosyops to specimens without the hypocone on M 3 and gave the new generic name Limnohyops to those with one. Earle (1891; 1892) recognized both Limnohyops and Palaeosyops as valid genera as did Osborn (1908; 1929). Osborn (1929) diagnosed the genus Limnohyops as follows: Brachycephalic; grinding teeth persistently brachydont; conules on the molars persistent, usually lophoid; third superior molar subquadrate and usually with distinct hypocone. Proportions of skull and skeleton moderately robust. Manus slender. Five sacral vertebrae (type). Osborn's (1929) formal diagnosis for the genus Palaeosyops, which he incorrectly characterized as specific rather than generic characters (p. 312), was very similar to the above: Brachycephalic. Grinding teeth persistently brachydont; metaconules on the molars persistent or absent; third superior molar without hypocone. Skull and skeleton robust; feet broad; manus with well-developed fifth digit; lunar resting subequally on magnum and unciform. Four sacral vertebrae. Osborn (1929, p. 302) stated that the ancestral members of these two genera from Bridger B (Blacks Fork Member of the Bridger Formation) are difficult to distinguish from one another and elsewhere (p. 303) commented that the early species of both genera are so similar that they might be included within a single genus. According to Osborn, however, distinctions gradually began to develop between the two genera until, in the upper strata of the Bridger Formation, the two forms are quite distinct. Osborn listed ten characters (pp. 302–303) that supposedly distinguish species of Limnohyops and Palaeosyops from higher geologic levels (such as P. robustus and L. laticeps from Bridger D). These characters (not quoted verbatim) are: 1. Upper and lower molars of Palaeosyops relatively larger, more rounded, and more robust. 2. Vertical striations on the cones of the upper and especially lower molars more distinct in Palaeosyops. 3. Conules on M 1–2 of Palaeosyops more variable, more rounded, and separate; in Limnohyops more constant, lophoid, ridged, or conjoined with the protocone and hypocone. Osborn noted that this distinction is not always reliable. 4. In Limnohyops hypocone of M 3 typically present; in Palaeosyops, typically absent. In Limnohyops metaconule of M 3 extremely reduced (owing to the large size of the adjacent hypocone); in Palaeosyops metaconule usually present and sometimes in such close proximity to the raised posterior cingulum that it appears similar to a hypocone (Osborn called such a structure a "pseudohypocone"). Thus the M 3 of Limnohyops is more quadrate and that of Palaeosyops is generally more triangular. 5. In Palaeosyops parastyle rounded and obliquely placed across the outer angle of the crown; in Limnohyops parastyle sharp and extending outward as a ridge. 6. In Palaeosyops nasals taper toward the extremities and are more pointed, while in Limnohyops the sides of the nasals are more parallel and they are more truncate at the extremities. 7. In Palaeosyops the suborbital bar is rounded and the maxillary process extends across its lower side as a broad splint. In Limnohyops the bar is more depressed and slightly rectangular in section and the maxillary process extends across its lower side as a thin splint. 8. In Palaeosyops there is a strong median convexity near the frontoparietal junction, while in Limnohyops the top of the cranium is slightly concave. 9. The sagittal crest of Palaeosyops is lower, broader, and passes more rapidly into the temporal ridges whereas in Limnohyops the crest is higher and thinner and extends well forward before spreading into the temporal ridges. 10. Male jaws of Palaeosyops have a more prominent, massive chin and shorter insertion for the digastric than male skulls of Limnohyops. The rami of Palaeosyops (seen from below) are more massive than those of Limnohyops and the anterior border of the coronoid process in Palaeosyops is broader. In more progressive stages of Palaeosyops the anterior border of the coronoid process is hollowed out in front while in progressive stages of Limnohyops the process is narrower, less deeply excavated, and "lies more to the outer side of the line of the molar teeth". Despite Osborn's recognition of Palaeosyops and Limnohyops as distinct genera, he noted (1929, p. 303) that the divergence between Palaeosyops and Limnohyops is far less than that observed within the modern genus Cervus. Mader (1989) concluded that Palaeosyops and Limnohyops are synonymous and stated that most of the generic distinctions cited by Osborn may be attributed to the vagaries of preservation or to individual variation. Gunnell and Yarborough (2000) also regarded Palaeosyops and Limnohyops as synonyms. The following can be attributed to individual variation and probably sexual dimorphism in the above characters: the size and massiveness of the molars, the distinctiveness of the striations on the molars, the shape of the sagittal and temporal crests (see Mader 1989), and the shape and massiveness of the lower jaw (characters 1, 2, 9, and 10). The shape of the parastyle (character 5) is also probably attributable to individual variation and possibly sexual dimorphism, but may also reflect differences in wear. The presence or absence of a hypocone on M 3 (character 4) is attributable to individual variation, but is not a sexually dimorphic character. Osborn was incorrect in his assertion that skulls of " Limnohyops " lack the frontoparietal convexity or dome (character 8). Although he illustrated a skull (Osborn 1929; Figs. 256, 259) that clearly shows a concave rather than convex forehead, the specimen in question (AMNH 11687) is almost crushed flat and this cranial morphology cannot be inferred. As previously noted (Mader 1989), the frontoparietal area is not well preserved in any of the specimens that Osborn referred to Limnohyops, with most being badly damaged or missing entirely. The dome appears to be present in all specimens of Palaeosyops, but is more prominent in the supposed males. The most convincing character used by Osborn to distinguish Limnohyops from Palaeosyops is the shape of the suborbital bar and the configuration of the suture pattern between the jugal and maxilla (character 7). Figure 7 illustrates two specimens showing these suture patterns: AMNH 5104, which Osborn referred to Limnohyops (type of L. laevidens); and AMNH 1516, which Osborn referred to Palaeosyops. In AMNH 1516 a wide flange of the maxilla extends below the jugal and forms the ventral surface of the zygomatic arch beneath the orbit. In AMNH 5104 only a slender projection of the maxilla extends onto the zygomatic arch, and the suture between the jugal and maxilla has a distinct Z-shaped pattern. Furthermore, the suborbital part of the zygomatic arch is broadly rounded in AMNH 1516 and is somewhat angular in AMNH 5104. Although seemingly excellent distinguishing characteristics, these most likely reflect preservational rather than taxonomic differences. In both specimens the morphology of the jugal beneath the orbit is the same and the uppermost contact between the jugal and maxilla in AMNH 5104 is in the same position as the long oblique contact between the jugal and maxilla in AMNH 1516. I posit that the morphology of both specimens was originally the same but, in AMNH 5104 the ventral part of the wide flange of the maxilla beneath the jugal has been broken away revealing the bottom part of the Z-shaped pattern normally concealed beneath. The ventral part of the maxillary flange is responsible for the roundness of the suborbital bar cited by Osborn as a character for Palaeosyops. When this flange is broken away, however, it results in the angular morphology that Osborn attributed to Limnohyops. Figure 8 illustrates AMNH 5104 showing my suggested reconstruction of the jugal-maxilla contact in this specimen. At least one other specimen that Osborn referred to Limnohyops (AMNH 11687, type of L. priscus) appears to have the jugal-maxillary region broken in a manner similar to that of AMNH 5104. Osborn recognized five valid species of Limnohyops and eight of Palaeosyops. These species were generally delineated by size, morphology of the premolars (shape of P 2, presence of a mesostyle on some of the premolars, and presence of two lingual cusps on P 2), and by the shape of the skull. The differences in premolar morphology cited by Osborn are trivial, however, and many of the differences in cranial morphology are the result of taphonomic deformation. In 1919 Osborn described a fragmentary skull (AMNH 17412, Figure 9) from the Huerfano Basin and identified it as a form ancestral to Metarhinus, which he named Eometarhinus ("Dawn Metarhinus "). In 1929 Osborn upheld this identification, but Robinson (1966), Wallace (1980), Mader (1989; 1998), and Gunnell and Yarborough (2000) synonymized Eometarhinus with Palaeosyops. Because all of the Huerfano material referred to Palaeosyops is rather poorly preserved it is difficult to demonstrate with certainty that it represents the same genus as Palaeosyops from the Bridger Formation. Although the Huerfano material is here considered to be correctly referred to Palaeosyops, I have previously questioned whether they are truly the same (Mader 1989). The upper part of the Huerfano Formation, therefore, preserves the earliest known record of Palaeosyops in North America. Unfortunately, only a few specimens have been collected from this stratigraphic level and I have data for only two individuals: AMNH 17411 and AMNH 17425. The Blacks Fork Member of the Bridger Formation is stratigraphically higher than the Huerfano Formation and is divisible into two stratigraphic levels: Bridger A and Bridger B. The sample of Palaeosyops from Bridger A that was examined for the present study includes some well-preserved cranial material, but is rather small in size and I have collected data for only three individuals from this level: AMNH 5107 (the type of P. fontinalis), UW 3039, and UW 3091. Most of the Palaeosyops material known from the Blacks Fork Member of the Bridger Formation is from Bridger B. I have data for twenty five individuals from this higher level. The Twin Buttes Member of the Bridger Formation overlies the Blacks Fork Member and is similarly divisible into two stratigraphic levels: Bridger C and Bridger D. Altogether data for 16 individuals from the Twin Buttes Member were collected for this study: 9 from Bridger C, 4 from Bridger D, and 3 from uncertain stratigraphic levels within the unit. The sample sizes of Palaeosyops from the Huerfano Formation (assuming the generic assignment is correct) and Bridger A assembled for the present study are too small to make a statistical analysis meaningful. Thus it is not practical to compare specimens from the Huerfano Formation against those from Bridger A using t -tests, nor is it profitable to examine summary statistics for specimens of Palaeosyops from each level. The most complete specimen of Palaeosyops from Bridger A examined for this study (UW 3091, Figure 10) appears to be rather different compared to specimens from Bridger B and may be taxonomically distinct. Compared to specimens of Palaeosyops from Bridger B, the lingual cusp on the second upper premolar of UW 3091 is very poorly developed and the metacone is almost lacking (although not all specimens of Palaeosyops from Bridger A have a P 2 that is as structurally plesiomorphic). Furthermore, the distinct cranial convexity that I have regarded (Mader 1989; 1998; present paper) as a synapomorphy of Palaeosyops appears to be very small and may be absent entirely (it is difficult to be certain because of crushing). There is some evidence of a slight swelling in the fronto-parietal region, however (see Figure 10). Gunnell and Yarborough (2000) have also described a specimen of Palaeosyops from the lower Bridger (UM 94880) with a very small dome. The small dome (compared to specimens of Palaeosyops from higher levels) could be a species characteristic, but it is also possible that it is a characteristic of females (Mader 1989). Other cranial and dental characters of UW 3091 closely match those of specimens from Bridger B including a strongly brachycephalic skull and robust, sharply downturned zygomatic arches. The nasals are missing from the specimen, however, and it is not known whether they are strongly arched and distally tapered as in specimens of Palaeosyops from Bridger B. Gunnell and Yarborough (2000) noted that the nasals of UM 94880 are curved ventrally, but do not appear to taper distally. If correct, then distally tapered nasals could not be a synapomorphic character of Palaeosyops (as formulated here), but would be a shared derived character of the more derived Palaeosyops species (P. paludosus and P. robustus). Gunnell and Yarborough’s specimen is crushed, however, (which could flatten and, thus, widen the tips of the nasals) and the type of “ Eometarhinus ” huerfanensis (here referred to Palaeosyops) has nasals that taper distally (see Figure 9). Because of the small size of specimens of Palaeosyops from Bridger A and the retention of plesiomorphic conditions in at least one specimen of Palaeosyops from this level (UW 3091), I provisionally accept the specimens from Bridger A as representing a species that is distinct from specimens from Bridger B. The type of P. fontinalis is from Bridger A, and I tentatively refer all of the Palaeosyops material from this level to that species. I also tentatively refer specimens of Palaeosyops from the Huerfano Formation to P. fontinalis because of their relatively small size and because there is no basis at present for distinguishing them from specimens of Palaeosyops from Bridger A. Many more fairly complete specimens of Palaeosyops from Bridger A and from the Huerfano Formation will have to be collected and analyzed before either of these conclusions can be accepted with reasonable certainty. If it should later prove that the material from the Huerfano Formation represents a distinct species, then the name P. huerfanensis (Osborn) could probably be applied to it. Table 7 presents the summary statistics for the sample of Palaeosyops from Bridger B. Almost 90 % of the individual coefficients of variation fall within the ideal range of 4 to 10. Three variables (excluding diastema length) have values of V greater than 10 (rounded to the nearest whole number) and one has a value of V less than 4. Although the average coefficient of variation for the sample is slightly high (6.7) it is within the range that I accept for a single species. Two out of the three variables that have values of V greater than 10 are measurements of canine size. Canine size is often sexually dimorphic in perissodactyls and it is possible that this factor accounts for the high individual values of V and perhaps for the relatively high average value of V. Although I have previously stated that canine size is not sexually dimorphic in brontotheres (Mader 1989) I have since concluded that canine size is sexually dimorphic in at least some, and possibly all, brontotheres (Mader 1998). Gunnell and Yarborough offer evidence suggesting that canine size may be dimorphic in Palaeosyops (see Gunnell & Yarborough 2000, Fig. 12). If canine size is excluded from the calculation of the average value of V for the sample, then the average value becomes 6.4, which is within the ideal range suggested by Simpson et al. (1960). a Based, whenever possible, on an average of left and right measurements. b Excluding Diastema Length. Analysis of the coefficient of variation strongly suggests that the sample is homogeneous and represents only a single species. It is surprising, therefore, that cluster analysis has revealed the presence of two or more size groups among the specimens in the sample. A cluster analysis of all of the variables listed in Table 7 results in a dendrogram (Figure 11) in which all of the specimens are distributed in an essentially homogeneous manner. If, however, cluster analyses are performed on certain groups of variables, then size groups of specimens begin to emerge. If, for example, a cluster analysis is performed using only the length of the cheek tooth series, length of the cheek tooth series exclusive of P 1, length of the molar series, and the basilar length of the skull, then a dendrogram results in which three groups are delineated (Figure 12). Two of these groups (labeled Group 1 and Group 2 on the diagram) join at a distance of 2.5 millimeters and are then joined by a third group (Group 3) at 4.0 millimeters. One specimen (AMNH 5102) groups out separately joining the others at a distance of 7.25 millimeters. If a third cluster analysis is performed using only the length and width of the first upper molar, then only two distinct size groups emerge (Figure 13). The size difference between these two groups is extremely small, however, and both join on the dendrogram at a distance of only one millimeter. It is difficult to determine from these cluster analyses how many size groups are actually present in the sample. Because the cluster analysis of the first upper molar resulted in the sharpest delineation of size groups, the groups suggested by this analysis were analyzed further. T -tests (Tables 8 and 9) confirm that for many variables (length of cheek tooth series, length of cheek tooth series exclusive of P 1, length of molar series, width of M 3, length and width of M 2 and M 1, and width right P 4) the means of the two size groups suggested by the dendrogram in Figure 13 are significantly different. Because the length of the premolar series and all but one of the individual premolar measurements show no significant difference between the two size groups, it is probable that molar dimensions account for the significant difference observed for the length of the cheek tooth series (with or without P 1). a Based, whenever possible, on an average of left and right measurements. b There is no variance in at least one of the two groups being compared. Taking all t -tests together, there is an 80 % chance (see Methods section) that at least one of these significant results is invalid (i.e., a false rejection of the null hypothesis). If, however, the error analysis is restricted to only those measurements that involve the molars (length of cheek tooth series, length of cheek tooth series exclusive of P 1, length of molar series, and length and width of individual molars) then there is only a 54 % chance that at least one of the significant results is due to a Type I error. a Based, whenever possible, on an average of left and right measurements. b Insufficient data for t -test. C Separate t -test The summary statistics for the two size groups suggested by the dendrogram in Figure 13 are presented in Tables 10 and 11. In Table 10, 75 % of the individual values of V (rounded to the nearest whole number) for the larger-size group are within the range expected for a single species. The average value of V for the sample (exclusive of

Brontotheriidae Marsh 1873

Family BRONTOTHERIIDAE Marsh 1873 Discussion: Mader (1989; 1998) divided the Brontotheriidae into two relatively large monophyletic subfamilies: the Dolichorhininae and the Brontotheriinae (= Telmatheriinae, sensu Mader 1989). Eotitanops and Palaeosyops were resolved as sister genera to these subfamilies, but were not found to comprise a monophyletic taxon. Recent phylogenetic analyses by Mihlbachler (2008) generally support this conclusion. Eotitanops and Palaeosyops are accorded their own subfamilies in the present revision.Published as part of Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), pp. 1-43 in Zootaxa 2339 on page 3, DOI: 10.5281/zenodo.19327

Palaeosyops paludosus Leidy 1870

Species Palaeosyops paludosus Leidy 1870 = P. major Leidy 1871 = P. minor Marsh 1871 a? = P. montanus (Marsh 1871 b) = P. humilis Leidy 1872 a = P. laevidens Cope 1872 = P. longirostris Earle 1892 = P. priscus (Osborn 1908) = P. matthewi (Osborn 1908) = P. monoconus (Osborn 1908) Lectotype: USNM 759, a lower second molar. Referred specimens: AMNH 1561, AMNH 5102, AMNH 5104 (lectotype of Palaeosyops laevidens), AMNH 11679 (type of Limnohyops monoconus), AMNH 11684 (type of Limnohyops matthewi), AMNH 11687 (type of Limnohyops priscus), AMNH 12182, AMNH 12680, AMNH 13032, AMNH 19236, USNM 13451, USNM 26115, USNM 26117, USNM 26127, USNM 26129, USNM 26130, USNM 26131, USNM 26132, USNM 26141, USNM 26146, USNM 26147, USNM 26170, UW 3094, UW 3154, YPM 11137. Diagnosis: Species of Palaeosyops intermediate in size between P. fontinalis and P. robustus (length P 2 to M 3 is approximately 129 to 161 mm). Discussion: The correct name holder for this species is USNM 759, the lectotype selected by Osborn (1929). Osborn (1929) also designated a lower jaw (AMNH 11680) as a " neotype " for the species but, because the original type is still preserved, this jaw has no nomenclatural significance and is merely a referred specimen (Article 75, International Code of Zoological Nomenclature, Ride et al. 1999). Similarly, the skull, jaw, and postcranials (UM 98890) that Gunnell and Yarborough (2000) designated as a “ neotype ” of P. paludosus cannot be recognized as the name holder under the provisions of the International Code. As indicated above in the Discussion section for the genus Palaeosyops, all of the Palaeosyops material from Bridger B is provisionally referred to the species P. paludosus. At present P. paludosus is poorly distinguished from both P. fontinalis and P. robustus. As a group, specimens of P. paludosus are intermediate in size between specimens of P. fontinalis and P. robustus but there is considerable size overlap. Thus, large specimens of P. fontinalis equal or exceed the size of smaller specimens of P. paludosus and large specimens of P. paludosus equal or exceed the size of small specimens of P. robustus. One year after Leidy described the type of Palaeosyops paludosus he named a new species of Palaeosyops, P. major, based on a pathologic lower jaw (ANSP 10421) lacking all of the dentition (Leidy 1871). In 1929, Osborn designated a " neotype " skull (AMNH 12182) and jaw (AMNH 12181) for this species, but once again the original type is still preserved and Osborn's skull and jaw are simply referred specimens. The type of P. major is identifiable as a specimen of Palaeosyops but is virtually useless as a type. If at some future date more than one species of Palaeosyops should be recognized in Bridger B, then P. major would probably have to be regarded as a nomen dubium. In the same year, Marsh (1871 a) described a right lower molar from Grizzly Buttes, which he identified as a new species of Palaeosyops, P. minor. I have not had the opportunity to examine this specimen, but assuming that Marsh was correct in identifying it as a brontothere, then it should be referred to P. paludosus since this is the only brontothere species that I recognize from this geologic level (Blacks Fork Member of Bridger Formation). Thus I tentatively regard P. minor as a junior synonym of P. paludosus. Palaeosyops minor Marsh is a primary senior homonym of P. minor Earle (1891), which Osborn (1929) also referred to P. paludosus. As a junior homonym, the name P. minor Earle is invalid (Article 57.2, International Code of Zoological Nomenclature, Ride et al. 1999). Marsh (1871 b) described teeth and parts of a postcranial skeleton, which he identified as a new species of carnivore, Canis montanus. Of this material Osborn selected a second lower premolar (misidentified by Marsh as a last upper premolar) as a lectotype for the species and correctly recognized that it is a specimen of Palaeosyops. Once again, the locality (Grizzly Buttes) places the specimens in the Blacks Fork Member of the Bridger Formation and, thus, I recognize P. montanus as a junior synonym of P. paludosus. In 1872 Leidy described a small tooth from "Dry Creek Canyon" forty miles (64 km) from Fort Bridger, Wyoming, which he identified as a new species of Palaeosyops, P. humilis (Leidy 1872 a). At first Leidy identified this tooth as a molar, but later correctly recognized that it is actually a deciduous premolar. Osborn (1929) suggested that this specimen is from Bridger C, and if this is the case, then it should be referred to P. robustus. The locality description, however, suggests to me that the specimen is probably from exposures of Bridger B along either Dry Creek or Little Dry Creek forty miles (64 km) west of Fort Bridger (see map of the Green River Basin in West 1976). In 1872 Cope also named a new species of Palaeosyops, P. laevidens, based on two cotypes. One specimen, AMNH 5104, was from Cottonwood Creek in the Green River Basin and the other specimen, AMNH 5105, was from Bitter Creek in the Washakie Basin. Because Cope (1885) "selects, describes, and figures" AMNH 5104 as the " type ", Osborn (1929) recognized this specimen as the lectotype of the species. AMNH 5104 is from Bridger horizon B and is referred, therefore, to P. paludosus in the present paper. In 1892 Earle named a new species of Palaeosyops, P. longirostris, based on a partial jaw (YPM-PU 10275) from Cottonwood Creek in the Green River Basin. The trivial name was in allusion to the supposedly great posterior extension of the lower jaw behind the last molar. Unfortunately, much of the type specimen may be lost. I have only been able to locate two fragments of the specimen and could find none of the teeth. Since deposits along Cottonwood Creek belong to Bridger B, I refer this specimen to P. paludosus. Osborn (1908) named three new species of " Limnohyops " from Bridger B the types of which were all collected from Grizzly Buttes. " Limnohyops " priscus was based on a severely deformed skull (AMNH 11687) with well-preserved dentition. In 1929 Osborn provided a "partial reconstruction" of this specimen (1929, Fig. 259) that is mostly imaginary. The specimen is almost crushed flat and very little of the cranial morphology can be observed. " Limnohyops " matthewi was based on the posterior part of a skull (AMNH 11684), but most of the characters that Osborn (1908; 1929) used to define the taxon (high and narrow occiput, postglenoid and posttympanic processes in close contact, and shape of the temporal fossae) are actually the result of taphonomic deformation in the type. " Limnohyops " monoconus was based on a fragmentary skull (AMNH 11679) and was distinguished from other specimens of " Limnohyops " by the absence of the hypocone on M 3. Palaeosyops paludosus is the only species of Palaeosyops from Bridger B that I recognize as valid, although cluster analysis does suggest more than a single size group is present (see Discussion section for the genus Palaeosyops). Gunnell and Yarborough (2000) recognized a second valid species from this level: P. laevidens (here a junior synonym of P. paludosus). Specimens assigned by Gunnell and Yarborough to P. paludosus and P. laevidens do not correspond to the size groups delineated in Figures 12 and 13. According to Gunnell and Yarborough (2000) Palaeosyops paludosus is larger in size (especially the premolars and first molar) than P. laevidens and has more molarized premolars. My impression, however, is that the premolar morphology is not discretely different among specimens that they place in the two species and most premolar and molar size ranges overlap (based on their published data). Given that the coefficient of variation for all specimens from Bridger B falls within the range of a single extant mammalian species (see Discussion section for the genus Palaeosyops), P. paludosus and P. laevidens should probably be regarded as synonyms.Published as part of Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), pp. 1-43 in Zootaxa 2339 on pages 37-38, DOI: 10.5281/zenodo.19327

The systematics and phylogeny of North American Eocene brontotheres (Mammalia:Perissodactyla)

Although extensively studied in the late nineteenth and early twentieth centuries, the extinct perissodactyl family Brontotheriidae has remained a poorly understood group and most recent workers have pointed out the need for a major systematic revision. The present dissertation is the first comprehensive revision of North American Eocene (Wasatchian - Duchesnean) brontothere species in over sixty years. Brontotheres (=titanotheres) are defined by the characteristic bunoselenodont pattern of the upper molars in which there is a well-developed W-shaped ectoloph and essentially isolated lingual cusps. Exclusive of the most primitive brontothere genus, Eotitanops, brontotheres are further defined by a shortening of the face; the presence of distinctive triangular-shaped, subcaniniform incisors; and a deep lateral nasal incision that is broadly bordered by the maxilla. In this dissertation thirteen North American Eocene brontothere genera are recognized as valid: Eotitanops, Palaeosyops, Telmatherium, Mesatirhinus, Metarhinus (=Rhadinorhinus), Sphenocoelus (=Dolichorhinus), Protitanotherium, Diplacodon progressum Peterson (a new generic name for this taxon will be published in the near future), Eotitanotherium, Notiotitanops, Duchesneodus, Sthenodectes, and Metatelmatherium. Within the Brontotheriidae four subfamilies are recognized: Eotitanopinae (Eotitanops), Palaeosyopinae (Palaeosyops), Dolichorhininae (Mesatirhinus, Metarhinus, and Sphenocoelus), and Brontotheriinae (Telmatherium, Protitanotherium, Diplacodon progressum, Eotitanotherium, Notiotitanops, and Duchesneodus). Diplacodonts and eubrontotheres are recognized as valid subgroups of the Brontotheriinae. An hypothesis of relationship for brontotheres is presented in the form of a cladogram. To determine whether other, equally parsimonious hypotheses of relationship may have been overlooked, the characters used to construct the cladogram were analyzed using the phylogenetic analysis program PAUP. The PAUP analysis produced three cladograms, all of which were essentially identical to the original hypothesis of relationship. It was concluded, therefore, that no other equally parsimonious cladograms had been overlooked. The computer generated cladograms had a consistency index of 100%, indicating that they are highly corroborated hypotheses of relationship

Selection of a lectotype for Brachycrus laticeps mooki Schultz and Falkenbach (Mammalia, Artiodactyla, Merycoidodontidae)

Mader, Bryn J. (2017): Selection of a lectotype for Brachycrus laticeps mooki Schultz and Falkenbach (Mammalia, Artiodactyla, Merycoidodontidae). Zootaxa 4323 (3): 415-418, DOI: https://doi.org/10.11646/zootaxa.4323.3.

Palaeosyops robustus Marsh 1872

Species Palaeosyops robustus (Marsh 1872) = P. laticeps Marsh 1872 = P. diaconus Cope 1873 b = P. leidyi Osborn 1908 = P. grangeri Osborn 1908 = P. copei Osborn 1908 Holotype: YPM 11122, a fragmentary skull. Referred specimens: ACM 1794, AMNH 1544 (type of P. leidyi), AMNH 1554, AMNH 1558, AMNH 1580, AMNH 2361, AMNH 5105, AMNH 5106 (type of P. diaconus), AMNH 11678, AMNH 11683, AMNH 11708 (type of P. copei), AMNH 11710, AMNH 12185, AMNH 12189 (type of P. grangeri), AMNH 12190, UCM 19489, USNM 6704, USNM 12694, USNM 13454, USNM 13464, USNM 13465, USNM 13466, USNM 16660, USNM 16661, USNM 16690, USNM 26120, USNM 26138, YPM 11000 (tentatively included, type of P. laticeps), YPM 11150, YPM-PU 10009. Diagnosis: Species of Palaeosyops distinguished from P. fontinalis and P. paludosus by its larger size (length P 2 to M 3 is approximately 150 to 165 mm). Discussion: As indicated in the Discussion section for the genus Palaeosyops, I recognize only a single valid species of Palaeosyops from the Twin Buttes Member of the Bridger Formation (Bridger C and D). Because " Limnohyus " robustus Marsh (1872) is the first species of Palaeosyops that is based on a type reliably known to have been collected from this level I have referred all specimens of Palaeosyops from the Twin Buttes Member of the Bridger Formation to this taxon. In the same paper, however, Marsh (1872) also described another new species of Palaeosyops, which he named P. laticeps. This specimen was recorded from "Marsh's Fork", approximately fifteen miles (24 km) from Fort Bridger. Although there are several creeks located ten to fifteen miles (16–24 km) southwest of Fort Bridger, there is no creek known as "Marsh's Fork". It is not certain, therefore, which stratigraphic horizon this specimen is from, but if it was collected in the vicinity of Cottonwood Creek or Black's Fork, then it is probably from Bridger B (Blacks Fork Member). However, if the distance is accurately recorded as fifteen miles (24 km), then the locality would almost certainly be in the Twin Buttes Member. The Sage Creek White Layer, which is the boundary between Bridger B (Blacks Fork Member) and Bridger C (Twin Buttes Member) is found in deposits located approximately eleven to twelve miles (18–19 km) from Fort Bridger. Because of the uncertainty of the stratigraphic level I only tentatively regard P. laticeps as a synonym of P. robustus. In accordance with the Principle of First Reviser (Article 24.2. 1, International Code of Zoological Nomenclature, Ride et al. 1999) I select the name Palaeosyops robustus as having priority over the name P. laticeps, as this will best serve nomenclatural stability (Recommendation 24 A), because the stratigraphic level from which the type of P. laticeps was collected is uncertain and P. laticeps could thus be a junior synonym of P. paludosus from Bridger B. It should be noted that Marsh discussed Palaeosyops laticeps before he discussed " Limnohyus " robustus in his 1872 paper, but the International Code does not recognize the concept of “page priority” (Nemésio 2007). Specimens of Palaeosyops from the Adobe Town Member of the Washakie Formation, which is chronologically equivalent to the Twin Buttes Member of the Bridger Formation, are also referred to P. robustus. Because of the small sample size of Palaeosyops from the Washakie Formation (n= 4) statistical analysis of the sample is not practical at this time. In the same year that Marsh described " Limnohyus " robustus, Leidy (1872 a) described the type of P. humilis, which Osborn (1929) alleged to be from Bridger C. As indicated in the discussion for the species P. paludosus, however, this specimen is probably from Bridger B and is thus referred to P. paludosus. In 1873 Cope described parts of two maxillae with some of the cheek dentition preserved (AMNH 5106), which he identified as a new species of Palaeosyops, P. diaconus (Cope 1873 b). This specimen is from Henry's Fork and is thus from the Twin Buttes Member of the Bridger Formation and represents P. robustus. In 1908, Osborn described three new species of Palaeosyops, all of which I refer to P. robustus. Palaeosyops leidyi was based on a well-preserved skull (AMNH 1544) from Henry's Fork; P. grangeri was based on a palate from Twin Buttes with the grinding teeth and parts of the lower jaw and skull preserved (AMNH 12189); and P. copei was based on a series of upper grinding teeth (AMNH 11708) from Henry's Fork at Lone Tree. In addition to Palaeosyops robustus, Gunnell and Yarborough (2000) recognized a second valid species of Palaeosyops from Bridger C: P. laticeps (here regarded as a synonym of P. robustus). Gunnell and Yarborough distinguished P. laticeps from P. robustus by the former’s smaller size (especially in upper premolar dimensions) and relatively distinct hypocones on M 3. However, specimens that Gunnell and Yarborough assign to the two species overlap in size for many variables (based on their published data). Furthermore, as indicated above, the distal part of the brontothere tooth row is highly variable and the size and morphology of the M 3 hypocone generally makes a poor diagnostic character. Thus, the weight of evidence suggests that there is a single species of Palaeosyops in the Twin Buttes Member of the Bridger Formation and its stratigraphic equivalents.Published as part of Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), pp. 1-43 in Zootaxa 2339 on pages 39-40, DOI: 10.5281/zenodo.19327

Palaeosyopinae

Subfamily PALAEOSYOPINAE Steinmann and Döderlein 1890 Included genera: Palaeosyops (= Limnohyus, Limnohyops, Eometarhinus). Diagnosis: Same as for member genus, Palaeosyops (see below). Sister taxon to all brontothere subfamilies except for the Eotitanopinae (see cladogram in Mader 1998, Fig. 36.5) Discussion: Palaeosyops is the sole member of the Palaeosyopinae (Steinmann & D derlein 1890). Because the subfamily Palaeosyopinae consist of only a single genus, the diagnosis of the subfamily does not differ from that of its member genus. Although Palaeosyopinae is recognized here as the valid name for this subfamily, it should be noted that the invalid name Limnohyinae predates it by fifteen years. Marsh (1875) compared Diplacodon to the "Limnohyidae," a previously unpublished family-group name. Marsh did not specify which taxa were to be included under this name, although it is obvious that it must include Lymnohyus (a junior synonym of Palaeosyops). According to the Principle of Coordination (Article 36, International Code of Zoological Nomenclature, Ride et al. 1999) this simultaneously established the subfamily name Limnohyinae with Marsh (1875) as the author. If the names Limnohyidae and Limnohyinae were to be valid, therefore, the subfamily name Limnohyinae would be a senior synonym of Palaeosyopinae. Although Marsh did not explicitly specify a type genus for the Limnohyinae, the subfamily name cannot be invalidated on this basis since the type genus (Limnohyus) can be clearly inferred from the construction of the name (Article 11.7. 1.1 International Code of Zoological Nomenclature). Furthermore, even though the genus Limnohyus is now recognized as a junior synonym of Palaeosyops, the family-group name Limnohyinae cannot be invalidated on this ground (Article 40.1). However, according to Article 11.7. 1.2, in order for a family group name to be valid, it must be clearly used by the original author to "denote a suprageneric taxon and not merely as a plural noun or adjective referring to the members of a genus...". The name Limnohyinae is invalid, therefore, because it is not clear from the context of Marsh's paper whether the term Limnohyidae was intended to apply to Limnohyus and some of the other brontothere genera then recognized (such as Palaeosyops and Telmatherium), or merely to the three species of Limnohyus described by Marsh and Cope up to that time.Published as part of Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), pp. 1-43 in Zootaxa 2339 on pages 15-16, DOI: 10.5281/zenodo.19327