Ceratopsid, Marsh, 1888

Kenneth Carpenter & D. Bruce Young, 2002, Late Cretaceous dinosaurs from the Denver Basin, Colorado, Rocky Mountain Geology 37, pp. 237-254 : 248-249

Ceratopsid genus and species indet. Figures 3 , 8 , and 17

Polyonax mortuarius Cope, 1874a

Bison alticornis Marsh, 1887

Ceratops alticornis Marsh, 1889

TYiceratops alticornis Hatcher, 1907

Ceratops montanus Marsh, 1888

TYiceratops galeus Marsh, 1889

Material. —AMNH 3950 dorsal centra, caudal centra, rib fragment, fibula fragment (holotype of Polyonax mortuaris- , Laramie Formation, East Bijou Creek); DMNH 2823 horn core, vertebra fragment (Denver Formation, Loc. 19); DMNH 25914 braincase (Denver Formation, Loc. 18); DMNH 25915 braincase, horn core fragment, frill fragment, dentary fragment with teeth (Denver Formation, Loc. 20); DMNH 27743 tooth (Denver Formation, Loc. 20); DMNH 27744 tooth (Denver Formation, Loc. 20); DMNH 29951 tooth (Denver Formation, Loc. 20); DMNH 33301 tooth (Denver Formation, Loc. 20); DMNH 33351 horn core, squamosal fragment (Laramie Formation, Loc. 8); DMNH 34291 left mandible (Denver Formation, Loc. 20); DMNH 34391 dentary, parietal fragment with base of horn core, left squamosal fragment (Denver Formation, Loc. 20); DMNH 34392 section of horn (Denver Formation, Loc. 20); DMNH 34595 radius? fragment (Denver Formation, Loc. 21); DMNH 44392 braincase (Denver Formation, Loc. 18); UCM 68914 right articular, posterior dorsal, neural spine, rih fragments, left humeral shaft, right partial ilium, right ischium, distal end of left ischium, left pubis (Denver Formation, Loc. 31); UCM 13746 horn core (Laramie Formation, Loc. 3); UCM 13749 horn core (Laramie Formation, Loc. 3); UCM 36398 humeral shaft, femoral shaft, rib fragments (Denver Formation, Loc. 22); UCM 42328 teeth (Laramie Formation, Loc. 1); UCM 43699 braincase (Laramie Formation, Loc. 2); UCM 47634 dentary fragment (Denver Formation, Loc. 27); UCM 47635 tooth (Denver Formation, Loc. 27); USNM 2410 nasal horn core (holotype of Triceratops galeus- , Arapahoe Formation, Loc. 11); USNM 4739 pair of frontals and horn cores (holotype of “Bison" alticornis ) Denver Formation, Loc. 29); and USNM uncataloged (Arapahoe Formation, Locs. 21, 22).

Description and discussion. —The hulk of the ceratopsian remains from the Denver Basin cannot he identified below family level. Most of the specimens indicate large, hence adult individuals. For example, the nearly complete dentary, DMNH 34391, is 52 cm in length and has 24 alveoli. A fragment of the predentary is present and is slightly curved, measuring 9.5 cm in length.

The material Cope (1874a) named Polyonax mortuaris from the eastern part of the Denver Basin is badly abraded and fragmented. In his review of the ceratopsians, Hatcher (1907) concluded that none of the material can he assigned to any of the known ceratopsian taxa, a point with which we concur. Marsh (1888) tentatively referred some bones from Colorado, which Lull (1907) identified as from the Arapahoe Formation as belonging to Ceratops montanus (these are uncataloged USNM specimens). Lull (1907) noted that the referral is improbable because of the vast age difference between the Judith River and the Arapahoe Formations. He further noted that the material is too fragmentary for positive identification.

Two holotypes of Marsh are also among the indeterminate ceratopsians. Marsh (1889) named Triceratops galeus for a nasal horn core collected from the Arapahoe Formation (Loc. 13). Hatcher (1907) noted that the specimen closely resembles that of the Torosaurus , but Lull (1933) noted that it also resembles that of a Triceratops skull, AMNH 5116 (compare Hatcher, 1907, fig. 111 with Forster, 1996, fig. 4A). He therefore considered T. galeus a nomen dubium, a point with which we concur. Another holotype is the famous pair of brow horn cores originally named by Marsh as Bison alticornis , but later referred by him (Marsh, 1889) to Ceratops alticornis . More recently, the specimen has been referred to Triceratops ( Hatcher, 1907; Lull, 1907; Lull, 1933; Ostrom and Welnhofer, 1986), although Forster (1996) noted that the horns cannot be assigned to Triceratops with certainty, a conclusion independently reached here. The horns most certainly could belong to Diceratops or Torosaurus as readily as to Triceratops .

A partial ceratopsian skeleton was collected from the flanks of South Table Mountain ( Fig. 8 ) by the Colorado School of Mines. The specimen has since been transferred to the University of Colorado Museum. The specimen includes pelvic material, which allows a composite restoration to be made ( Fig. 17 ). The pelvis is rather small compared to those in the Smithsonian collections from the Lance Formation.

Figures

Figure 3. (Caption on facing page.)

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 17. Restored pelvis of the ceratopsian shown in Figure 8 in right lateral view (pubis reversed). Scale bar = 10 cm.