Non-avian theropod phalanges from the marine Fox Hills Formation (Maastrichtian), western South Dakota, USA

John A Chamberlain Jr; Katja Knoll; Joseph J W Sertich

doi:10.7717/peerj.14665

Non-avian theropod phalanges from the marine Fox Hills Formation (Maastrichtian), western South Dakota, USA

PeerJ. 2023 Feb 7:11:e14665. doi: 10.7717/peerj.14665. eCollection 2023.

Authors

John A Chamberlain Jr^{1

2}, Katja Knoll³, Joseph J W Sertich^{4

5}

Affiliations

¹ Department of Earth and Environmental Sciences and Department of Biology, City University of New York, Graduate School and University Center, New York City, New York, United States.
² Department of Earth and Environmental Sciences, City University of New York, Brooklyn College, Brooklyn, New York, United States.
³ Paria River District, US Bureau of Land Management, Kanab, Utah, United States.
⁴ Smithsonian Tropical Research Institute, Panama City, Panama.
⁵ Department of Geosciences, Warner College of Natural Resources, Colorado State University, Fort Collins, Colorado, United States.

Abstract

We report here the first dinosaur skeletal material described from the marine Fox Hills Formation (Maastrichtian) of western South Dakota. The find consists of two theropod pedal phalanges: one recovered from the middle part of the Fairpoint Member in Meade County, South Dakota; and the other from the Iron Lightning Member in Ziebach County, South Dakota. Comparison with pedal phalanges of other theropods suggests strongly that the Fairpoint specimen is a right pedal phalanx, possibly III-2, from a large ornithomimid. The Iron Lightning specimen we cautiously identify as an ornithomimid left pedal phalanx II-2. The Fairpoint bone comes from thinly bedded and cross-bedded marine sandstones containing large hematitic concretions and concretionary horizons. Associated fossils include osteichthyan teeth, fin spines and otoliths, and abundant teeth of common Cretaceous nearshore and pelagic chondrichthyans. Leaf impressions and other plant debris, blocks of fossilized wood, and Ophiomorpha burrows are also common. The Iron Lightning bone comes from a channel deposit composed of fine to coarse sandstone beds, some of which contain bivalves, and a disseminated assemblage of mammal teeth, chondrichthyan teeth, and fragmentary dinosaur teeth and claws. We interpret the depositional environment of the two specimens as marginal marine. The Fairpoint bone derives from a nearshore foreset setting, above wave base subject to tidal flux and storm activity. The Iron Lightning specimen comes from a topset channel infill probably related to deposition on a tidal flat or associated coastal setting. The taphonomic history and ages of the two bones differ. Orthogonal cracks in the cortical bone of the Fairpoint specimen suggest post-mortem desiccation in a dryland coastal setting prior to transport and preservation in the nearby nearshore setting described above. The pristine surface of the Iron Lightning specimen indicates little transport before incorporation into the channel deposit in which it was found. The Fairpoint bone bed most probably lies within the Hoploscaphites nicolletii Ammonite Zone of the early late Maastrichtian, and would therefore have an approximate age of 69 Ma. The Iron Lightning bone is from the overlying H. nebrascensis Ammonite Zone, and is thus about one million years younger.

Keywords: Fox Hills Formation; Maastrichtian; Marine preservation; Non-avian theropod phalanges; South Dakota, USA.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Bone and Bones
Dinosaurs* / anatomy & histology
Fossils
Mammals
South Dakota
Tooth*

Grants and funding

This research was supported by the PSC-CUNY Research Award Program of the City University of New York (grant numbers 62274; 64246; 64263; 668230; and 669224). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.