Sallatherium REGUERO & CERDENO 2005

SALLATHERIUM ALTIPLANENSE REGUERO & CERDEÑO, 2005

Below we describe a new specimen of S. altiplanense with slightly worn teeth which complements the original description.

Diagnosis: Hegetotheriinae with nasals especially long and thin, not enlarged posteriorly. Labial groove on upper cheek teeth more medially placed than in Prohegetotherium. I1 enlarged, more oval in crosssection and more obliquely implanted than in Prohegetotherium, Hegetotherium and Hemihegetotherium. I2-I3-C more reduced than in Prohegetotherium and separated by diastemata, in contrast to Prohegetotherium and Hemihegetotherium, which have a closed dental series. P3-M3 with ovoid occlusal outline, different from the more quadrangular section of other hegetotheriines. Lower canine absent, i3 reduced, and a diastema separates i3 and p1. Lower p3 with anterior lobe longer than posterior lobe, in contrast to Prohegetotherium and Hemihegetotherium (Reguero & Cerdeño, 2005).

Holotype: UF 91621, partial skull and associated incomplete mandible.

Referred specimen: SAL 561, a right maxillary with P4-M3 (Fig. 23).

Description

SAL 561 represents a young adult as the teeth are very slightly worn and still present a pattern of fossettes. Referral of this material to S. altiplanense is difficult as young specimens of this species are not known so far. However, it presents cheek teeth that resemble hegetotheriids especially in their occlusal outline, which appear to be more regular than in Archaeohyrax. It also presents an M3 clearly smaller in surface area than M2 (Appendix S4, Table 5). These two characters are characteristic of hegetotheriids as compared with Archaeohyrax suniensis (see cladistic analysis) to which this specimen could have been referred in initial view (as they come from the same deposits and are of approximately the same size).

Moreover, the coexistence of the fossettes is very different to that exhibited in Archaeohyrax suniensis, which represents the most distinct difference with this taxon. SAL 561 presents simultaneously an isolated central fossette on M1-3. This never occurs in A. suniensis. Besides the central fossette, an anterior– labial accessory fossette is present on M2-3. The co-occurrence of the central fossette and the labial accessory fossettes (here, only the anterior one) never occurs on Archaeohyrax and Protarchaeohyrax molars (Croft et al., 2003; see also Discussion of our cladistic analysis). If the assignment of this specimen to Sallatherium is correct, it demonstrates that the original pattern of hegetotheriid cheek teeth presents the typical face pattern of typotherians.

Reguero & Cerdeño (2005: 680, fig. 6) referred to another hegetotheriid, Prohegetotherium schiaffinoi (Kraglievich, 1932), a specimen (MNHN-BOL-V 004152) from Salla with unworn upper cheek teeth. It also exhibits the co-occurrence of central and accessory fossettes. However, our re-examination of this specimen (quasi-unworn right P2-4) indicates that it is identical to unworn premolars of A. suniensis, a species to which it is referred here (Fig. 10). Patterson (1934b) described juvenile teeth of a hegetotheriid, the pachyrukhine Prosotherium, but they are very different from those of Sallatherium given that they never present the isolation of a central fossette.