DOLICHORHININAE Riggs 1912

Mader, Bryn J., 2008, A species level revision of Bridgerian and Uintan brontotheres (Mammalia, Perissodactyla) exclusive of Palaeosyops, Zootaxa 1837 (1), pp. 1-85 : 7-8

Subfamily DOLICHORHININAE Riggs 1912

(Includes Rhadinorhininae Osborn 1929)

Diagnosis. Brontotheres distinguished from all others by the presence of a suborbital protuberance (= infraorbital process). There is a tendency among all members of the subfamily to have relatively elongated molars.

Discussion. The subfamily name Dolichorhinae (emended to Dolichorhininae by Osborn 1929) was proposed by Riggs in 1912. Although Dolichorhinus , the type genus of this family-group name, is recognized as a junior synonym of Sphenocoelus in the present paper, the name Dolichorhininae remains a valid taxonomic term (Article 40, International Code of Zoological Nomenclature, Ride et al. 1999).

Mader (1989) diagnosed the subfamily Dolichorhininae by the presence of a suborbital protuberance and a reduced canine. I am now ( Mader 1998; present paper) less certain of the validity of this last character, however, because skulls of Sphenocoelus (= Dolichorhinus ) that I identify as males have relatively large canines. On skulls of Sphenocoelus that I identify as females, however, the canines are quite small and delicate.

Another character that distinguishes the dolichorhinine brontotheres from others is the tendency to have relatively elongated molars. This characteristic is found in all genera here assigned to the subfamily, but is not exhibited by all individuals. Thus, these dental proportions are not uniformly diagnostic of the subfamily, since some individual dolichorhinine brontotheres have relatively square teeth.

It will be noted from Figure 1 that, as a rule, members of the subfamily Dolichorhininae (black symbols) have teeth that are relatively elongated (plot below the line) while other brontotheres (white symbols) tend to have wider teeth (plot on or above the line). Some individual dolichorhinines, however, have teeth that are either square or are wider than they are long, while some non-dolichorhinine brontotheres have relatively elongated teeth.

Mihlbachler (2005) performed a phylogenetic analysis of brontotheres in which the Dolichorhininae as recognized by Mader (1989; 1998; present paper) was determined to be paraphyletic. Although there was much merit to this detailed analysis, I believe that there are several important problems with the characters that must be addressed. This is beyond the scope of the present paper, however. The validity of the Dolichorhininae was strongly supported in a phylogenetic analysis done by Mader (1991), in which twenty-one evolutionary steps were required to account for twenty-one character states (Consistency Index of 100%).

Figures

FIGURE 1. Scatter plots showing length of M2 plotted against width of M2 for five brontothere genera. The solid diagonal line that crosses both graphs represents the points at which the length and width of the tooth are equal. Specimens that plot out above the line have teeth that are wider than long, while specimens that plot out below the line have teeth that are longer than wide. Specimens that plot out directly on the line have teeth in which the length is equal to the width and are thus square in shape. Black symbols, subfamily Dolichorhininae; white symbols, other brontothere genera (Palaeosyops and Telmatherium).