Contributions to Geology 26.2

Preliminary report on Late Cretaceous mammals of the Kaiparowits Plateau, southern Utah

JEFFREY G. EATON Geology Department, Museum of Northern Arizona, Route 4, Box 720, Flagstaff, AZ 86001
RICHARD L. CIFELLI Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, OK 73019

Pages
45-56

Keywords
Kaiparowits Plateau, mammals, Utah, Cenomanian, Campanian, marsupials

Abstract
The Kaiparowits Plateau region has yielded Late Cretaceous mammalian faunas that range in age from the Cenomanian through the Campanian. The multituberculate taxon Paracimexomys is common throughout the section, Cimolodon becomes common in the upper part of the section, and Meniscoessus is rare or absent throughout the section. Spalacotheres and therians of "metatherian-eutherian grade" are an important component of the faunas. Among marsupials, peradectids are common, stagodontids are less common, and pediomyids are absent. The faunas of the Kaiparowits region are quite distinct from known approximately time equivalent faunas from the north (Milk River and Judith River faunas) suggesting marked latitudinal paleoenvironmental differences.

Taphonomy of Hazard Homestead Quarry (Ogallala Group), Hitchcock County, Nebraska

ANTHONY R. FIORILLO Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and Department of Vertebrate Biology, Academy of Natural Sciences of Philadelphia, 19th and the Parkway, Philadelphia, Pennsylvania 19103

Pages
57-98

Keywords
Hazard Homestead Quarry, Nebraska, bone bed, ungulates, carnivores

Abstract
A taphonomic investigation of a richly fossiliferous bone bed at Hazard Homestead Quarry in Hitchcock County, Nebraska, has provided new information on processes affecting attritional bone accumulations in a floodplain environment. A tabular body of poorly sorted sandstone and marl containing the remains of medial Miocene (Barstovian) medium- to large-sized ungulates and carnivores constitutes the site, which lies stratigraphically near the base of the Ogallala Group.

Orientation measurements obtained from 778 long bones and fragments in two excavations were plotted as stereographic projections. The orientations deviate slightly from a random distribution, but do not exhibit the strong preferential alignment shown by previous studies to be characteristic of primary fluvial accumulations. Trampling by Barstovian mammals during the formation of this site may be responsible for the distribution of orientations observed at Hazard Homestead. The nonrandom component of the orientations in Hazard Homestead Quarry may represent a remnant of a former current-induced pattern disrupted by trampling.

A census of the skeletal elements excavated from the site shows that less-dense bones (e.g. ribs, vertebrae) are only about one-third as numerous as expected in an unmodified assemblage of skeletons. Calculation of the quartz-grain equivalents for bones in the Hazard assemblage shows that all but the smallest and lightest elements are not in hydraulic equilibrium with the sediment enclosing them (i.e., they would not have been transported at the low current velocities implied by the fine- to medium-grained sandstone matrix). Thus, hydraulic winnowing is unlikely to have removed the "missing" elements and the low frequency of the latter must be attributed to other causes.

Close scrutiny of the surface condition of bones excavated from the site provides further clues to their preburial history. Most of the specimens are unabraded and unweathered, indicating that they suffered little or no transportation and only short subaerial exposure. Many, however, exhibit fresh-bone (spiral) breakage and recognizable tooth marks of carnivores, suggesting that the bone assemblage had been extensively scavenged. Another surface feature, not previously reported at paleontological sites, consists of numerous sets of shallow, subparallel scratches. Identical marks were produced on modern bones during trampling experiments carried out during this study, leading to the inference that the Hazard bone assemblage probably was extensively trampled prior to its final burial.

Distribution of the Heterohelicidae in Upper Cretaceous strata of the Western Interior

WILLIAM E. FRERICHS Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071

Pages
99-106

Keywords
planktic, foraminifera, Cretaceous, Western Interior, Heterohelicidae

Abstract
More than seventy species of planktic foraminifera have been identified from Upper Cretaceous strata of the Western Interior. Seventeen species belong to the Heterohelicidae, a family widely distributed in the Western Interior, with representatives found from the early Cenomanian to the late Maastrichtian. Species of the Heterohelicidae are particularly useful in Western Interior biostratigraphy in the late Santonian to the late Maastrichtian interval.