16 
Donald Baird and John R. Horner 
varieties of Late Cretaceous ornithischians are all too small for considera- 
tion. 
As Gilmore concluded, the sauropod dinosaurs are the only group to 
which this genus can be plausibly assigned. Judged ex pede Herculem by the 
mass of its tail, Hypsibema must have been a dinosaur of brontosaurian 
size, one worthy of a generic name meaning “high stride.” However, the 
common sauropods of the Cretaceous — the Titanosauridae — are 
characterized by procoelous caudal vertebrae with forward-set neural 
arches and prezygapophyses that project beyond the end of the centrum: 
this condition is exemplified by Alamosaurus from the Lower North Horn 
formation (Maestrichtian) of Utah (Gilmore 1946). Hypsibema must 
therefore belong to some other family, one in which the middle and 
posterior caudals are amphicoelous to amphiplatyan. Gilmore, after 
eliminating various possibilities, was unable to place the genus in any 
family but concluded that it might be assigned tentatively to the 
Camarasauridae on the basis of the “general make up” of the vertebrae. 
Neither extensive comparison nor expert advice has enabled us to im- 
prove on Gilmore’s treatment of the problem, so we must leave the family 
assignment open until more diagnostic material is found. 
Order ORNITHISCHIA 
Suborder ORNITHOPODA 
Family HADROSAURIDAE 
Hadrosaurinae indet. 
Figs. 2B-C, 4C-D, 7, 8 
As might be expected, bones of duckbill dinosaurs form a large percent- 
age of the total sample. Two mandibular fragments (ANSP 15306 and 
USNM 7096) from Phoebus Landing were described by Miller (1967: 
234). The first of these (Fig. 7) is part of a right lower jaw that includes 
the basal portion of the coronoid process externally and the posterior end 
of the grooved dentary (without teeth) internally. Also described by 
Miller (as an extremely large postzygapophysis) is a right coronoid 
process (ANSP 15329, Fig. 7) that evidently originated from a jaw com- 
parable in size to ANSP 15306. Although the two specimens cannot be fit- 
ted together, their identical coloring and size and the fact that they came 
from the same locality suggest that they may pertain to the same indi- 
vidual. 
Two hadrosaurian teeth (ANSP 15333) from Phoebus Landing are 
here described for the first time. A shed maxillary tooth (Fig. 2B) is of no 
descriptive use below the family level. The dentary tooth (Fig. 2C) is un- 
