Trachytherus sp.

Shockey, Bruce J., Gismondi, Rodolfo Salas, Gans, Phillip, Jeong, Annie & Flynn, John J., 2009, Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Perú, American Museum Novitates 3668, pp. 1-24 : 18-19

Trachytherus sp. (medium size)

Figure 8B ; table 5

MATERIAL: MUSM 350, skull (damaged basicranium) and mandibles ( Shockey et al., 2006: fig. 2); MUSM 963, left and right partial manus; and astragali MUSM 961, 962, and 966.

LOCALITY: All from the summit of Cerro Pan de Azúcar, near the point where the skull and jaws ( MUSM 350) was found (fig. 1: c on the map).

DESCRIPTION: A variety of postcranial elements referable to Trachytherus were found alongside the skull (MUSM 350), as well as an m3 of a different individual of Trachytherus that are referable to this midsize mesotheriid. Most of these elements likely do not represent the same individual as MUSM 350 since they appear to be from ontogenetically younger individuals. We refer the partial manus of MUSM 963 (fig. 8B), as well as some tarsals found nearby, to this unnamed taxon. A smaller mesothere manus (MUSM 965; fig 8C) may also pertain to this taxon, but we do not refer it to this taxon since it is so small that it likely represents a different species (see below).

The manus of this midsize trachytheriine (fig. 8B) is similar to that of cf. T. spegazzinianus from Cerro Mono of Moquegua (see fig. 1: g on map for locality; fig. 8A for the manus) and the manus of T. alloxus from Salla ( Shockey et al., 2007; identified there as T. spegazzinianus ). We note the unfused distal radius and ulna of MUSM 963, which indicates that even though it was found in close proximity to the skull (MUSM 350), it represents a different, ontogenetically younger individual, whereas the complete eruption of the M3 and the significant dental wear indicates that the MUSM 350 is a mature individual. The manus MUSM 963 is nearly identical to those of T. spegazzinianus and the small indeterminate species discussed below (fig. 8 A, C), save for its size intermediate between the two. Also, since neither the trapezoid nor Mc I were recovered, we cannot assert that the manus of this midsize taxon was pentadactyl like T. alloxus , cf. T. spegazzinianus (fig. 8A), and the small indeterminate species, but we note that even the Pleistocene Mesotherium had five digits on its manus ( Serres, 1867; Ameghino, 1891; Shockey et al., 2007.)

CF. TRACHYTHERIINAE

Small indeterminate species

Figure 8C ; table 5

MATERIAL: MUSM 965 right and left manus, the right being nearly complete, while the left is missing the trapezoid and trapezium and the metacarpals are fragmentary (fig. 8C); MUSM 966 astragalus.

LOCALITY: Collected in the upper Moquegua Formation, at the summit of Cerro Pan de Azúcar, near the skull of the midsize Trachytherus sp. ( MUSM 350) (fig. 1: c on the map).

DESCRIPTION: Fragments of postcranial elements of a very small trachytheriine were found near and among broken remains of specimens of the midsize species of Trachytherus . These may represent small individuals of that taxon or (more likely) may indicate that a third trachytheriinine species was present. These distinct elements do not represent an ontogentic difference between the manus of MUSM 965 and that of MUSM 963 from the same spot, since both are at the same stage of development (fused metacarpals and unfused distal radii and ulnae).

The sample size is too small to be conclusive, but we note several size discontinuities between these smallest indeterminate trachytheriines, the midsize Trachytherus sp. and cf. T. spegazzinianus (table 5). Postcranial elements referred to the midsize taxon have linear dimensions generally 15% to nearly 30% greater than the same regions of the small, indeterminate trachytheriine. Skeletal elements referred to T. spegazzinianus are much larger than both this diminutive trachytheriine and the midsize taxon.

We figure the left manus of this small trachytheriine and note its close similarity to the manus of both the large (cf. T. spegazzinianus ) and the midsize taxon (fig. 8) as well as that of T. alloxus ( Shockey et al., 2007) . These also are very similar to the manus of the Pleistocene mesotheriine Mesotherium ( Ameghino, 1891; Shockey et al., 2007).

Figures

Fig. 8. Trachytheriine autopodia. A, Nearly complete right manus of cf. Trachytherus spegazzinianus (MUSM 668); B, Carpal region of right manus of Trachytherus sp. (mid-sized species) (MUSM 963); C, right manus (missing digits and trapezoid) of trachytheriine, small indeterminate species, (MUSM 965); D, right pes (missing digits) cf. Trachytherus spegazzinanus of Moquegua (MUSM 668); E, line drawing of Trachytherus pes; and F, line drawing of Eutypotherium lehmannnitschei of Laguna Blanca, Chubut, Argentina (drawn from AMNH 14963, cast of a Museo de La Plata specimen).