Palaeosyops paludosus Leidy 1870

Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), Zootaxa 2339, pp. 1-43 : 37-38

Species Palaeosyops paludosus Leidy 1870

= P. major Leidy 1871

= P. minor Marsh 1871 a?

= P. montanus ( Marsh 1871b) = 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 P2 to M3 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 (1871a) 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 (1871b) 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 1872a) . 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 M3.

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.

Figures

FIGURE 12. Cluster dendrogram for specimens of Palaeosyops from Bridger B resulting from a cluster analysis of basilar skull length, length of cheek tooth series, length of cheek tooth series exclusive of P 1, and length of molar series. a, type of Limnohyops priscus; b, type of Limnohyus laevidens; c, type of Limnohyops monoconus.

FIGURE 13. Cluster dendrogram for specimens of Palaeosyops from Bridger B resulting from a cluster analysis of the length and width of the first upper molars. a, type of Limnohyops priscus; b, type of Limnohyops monoconus.