Tiuclaenus robustus Muizon & Cifelli, 2000

Muizon, Christian de, Billet, Guillaume & Ladevèze, Sandrine, 2019, New remains of kollpaniine “ condylarths ” (Panameriungulata) from the early Palaeocene of Bolivia shed light on hypocone origins and molar proportions among ungulate-like placentals, Geodiversitas 41 (25), pp. 841-874 : 856

Tiuclaenus robustus Muizon & Cifelli, 2000

DIAGNOSIS. — See Muizon & Cifelli (2000).

DESCRIPTION

A right mandible fragment bearing m2-3 (MHNC 13875) has been referred to Tiuclaenus robustus ( Fig. 10B, C ) essentially because, although structurally similar to the other species of Tiuclaenus ( T. minutus and T. cotasi), it differs from them in its size, distinctly larger, and in its greater massiveness. Furthermore, as is observed on the holotype (a mandible fragment with m2-m3, MHNC 1233), m3 of MHNC 13875 is proportionally shorter than in T. minutus and T. cotasi being barely longer than m2. An interesting feature of this specimen is the morphology of the roots of m2 and m3, which are long extending ventrally on more than 2.5 the height of the crown ( Fig. 10C ). Furthermore, the apices of the roots are markedly splayed with their posterior edges extending posteriorly, providing the extremity of the root a characteristic hammer-shape. Although the ventral edge of the dentary is partly broken, this morphology gives the impression that the root had to develop posteriorly because it was abutting the ventral edge of the mandibular canal.

Figures

FIG. 10. — A, Tiuclaenus minutus: partial right maxilla of with M1-3 (MHNC 13879), stereophotograph of occlusal view; B, Tiuclaenus robustus: partial right mandible with m2-3 (MHNC 13875), stereophotograph of occlusal view; C, the same in labial view. Scale bar: 5 mm.