Torosaurus, Marsh, 1891

Kenneth Carpenter & D. Bruce Young, 2002, Late Cretaceous dinosaurs from the Denver Basin, Colorado, Rocky Mountain Geology 37, pp. 237-254 : 247-248

cf. Torosaurus sp.

Figures 8 and 11

Material. -DMNH 17060 left dentary with articular, splenial, left scapula and coracoid, cervical, posterior dorsal, sacrum, anterior caudal, posterior caudal, ribs, left humerus, partial ilium, ilium fragment, right pubis, right ischium, fibula fragment, metatarsal (Laramie Formation, Loc. 9).

Description and discussion. — This ceratopsian specimen is tentatively referred to Torosaurus on the basis of the elongated humeral shaft below the deltopectoral crest ( Fig. 11 E, F ) and elongated posteromedial process of the coracoid ( Fig. 8 C ; compare Johnson and Ostrom, 1995, figs. 12.3-12.6, Hatcher et al., 1907, fig. 64-66, and Figs. 11 C, E, F ). Unfortunately, the frill, which has the most diagnostic features, is not present. If the identification is correct, this is the first record of Tbrosaurus in Colorado. Much of this specimen is illustrated because little Tbrosaurus material has been figured before.

The dentary is complete and retains all of the teeth, although some of them have slipped partially out of their alveoli ( Fig. 11 A, B ). The dentary is 63.5 cm long and the tooth row 47.3 cm. The articular is wedged between the tooth row and coronoid process. The vertebrae resemble those of other large neoceratopsians, such as Triceratops ( Hatcher et al., 1907), so are not figured. The scapula is proportionally short compared to dentary length, being about the same length (63 cm). In Triceratops , the dentary is apparently 75 percent the length of the scapula based on a skull and articulated skeleton (NSM PV20379). The scapula is 35 cm tall just posterior to the glenoid. The coracoid is nearly complete and has a distinct ventromedial projection (see Johnson and Ostrom, 1995, fig. 12.5) that is not seen in Triceratops . It is 27.3 cm long and over 43 cm tall.

The humerus is crushed, thereby distorting the deltopectoral crest and the medial humeral tuberosity ( Fig. 11 B, F ). The humerus has a midline length of 60 cm, is 37 cm wide proximally, and 28 cm wide distally. The pubis is missing its postpuhic process, hut otherwise it is relatively complete, although much covered with plaster of Paris. The ischium is missing both the proximal and distal ends.

Figures

Figure 8. Ceratopsian pelvicbones (UCM 68914) from Denver Formation. Right ilium lacking most of preacetabular blade in dorsal (A), lateral (B), medial (C), and ventral (D) views. Left pubis in lateral (E) and medial (F) views. Right ischium in medial (G) and lateral (IT) views. Scale bar = 10 cm.

Figure 11, left. Fossils referred to Torosaurus sp. (DMNH 17060), for­ merly known as Leyden Triceratops. Left dentary in lateral (A) and medial (S') views. Left coracoid (C), and left scapula (D). Crushed left humerus in anterior (E), and posterior (E) views. Right pubis (G) and ischium (FT). Scale bar = 10 cm.