Metarhinus fluviatilis, Osborn 1908

Mader, Bryn J., 2008, A species level revision of Bridgerian and Uintan brontotheres (Mammalia, Perissodactyla) exclusive of Palaeosyops, Zootaxa 1837 (1), pp. 1-85 : 29

Species METARHINUS fluviatilis Osborn 1908

= M. riparius Riggs 1912

Holotype. AMNH 1500 , a partial skull lacking the nasals.

Referred specimens. FMNH 12173 , FMNH 12187 , FMNH P 12186 (type of M. riparius ) , FMNH PM 3935 , UCM 44939, UCMP 81278 , YPM 13125 .

Diagnosis. Small species of Metarhinus with nasals that are broadly flared distally and constricted at the base giving them a distinctive spoon-shape.

Discussion. As indicated in the discussion above, the holotype skull of Metarhinus fluviatilis lacks the nasals and is, therefore, only provisionally accepted as representing the variety of Metarhinus with spoonshaped nasals. This conclusion is based solely on the diminutive size of the type specimen, which is smaller than any of the specimens of Metarhinus with spoon-shaped nasals for which I have data. The size of the skull is probably inconsistent with the possibility that it represents the variety of Metarhinus with tapered nasals because individuals with this nasal morphology appear to be larger than those with spoon-shaped nasals. If later work should demonstrate that the Metarhinus with spoon-shaped nasals does not represent the type species ( M. fluviatilis ) then the next available name for this taxon is probably M. riparius , which was based on a skull (FMNH P 12186) clearly possessing the spoon-shaped nasal morphology.

Mihlbachler (2005) suggested that, because the holotype of Metarhinus fluviatilis lacks nasals, it would be advisable to designate a neotype for the species in which the nasals are preserved. Mihlbachler proposed FMNH PM 12187, but this specimen can have no validity as a name-holder according to Article 75 of the International Code of Zoological Nomenclature ( Ride et al. 1999), since the original type specimen (AMNH 1500) is still preserved.