The distinctive theropod assemblage of the Ellisdale site of New Jersey and its implications for North American dinosaur ecology and evolution during the Cretaceous

Chase D. Brownstein

doi:10.1017/jpa.2018.42

Abstract

AbstractThe Cretaceous landmass of Appalachia has preserved an understudied but nevertheless important record of dinosaurs that has recently come under some attention. In the past few years, the vertebrate faunas of several Appalachian sites have been described. One such locality, the Ellisdale site of the Cretaceous Marshalltown Formation of New Jersey, has produced hundreds of remains assignable to dinosaurs, including those of hadrosauroids of several size classes, indeterminate ornithopods, indeterminate theropods, the teeth, cranial, and appendicular elements of dromaeosaurids, ornithomimosaurians, and tyrannosauroids, and an extensive microvertebrate assemblage. The theropod dinosaur record of the Ellisdale site is currently the most extensive and diverse known from the Campanian of Appalachia. Study of the Ellisdale theropod specimens suggests that at least four or more non-avian theropod taxa are represented at the site, including tyrannosauroids, ornithomimosaurs, several different morphotypes of dromaeosaurids that are the first of that clade described from New Jersey, and indeterminate theropods. The specimens are important for increasing current knowledge about the theropod diversity of the Atlantic Coastal Plain (ACP) during the Campanian by representing the most speciose assemblage of the group during the time in the ACP as well as for shedding light on Appalachian dinosaur ecology and biogeography generally.

Highlights

The landmass of Appalachia was created when the Western Interior Seaway flooded the interior of North America and separated the eastern portion of the continent from the west midway through the Cretaceous (Roberts and Kirschbaum, 1995; Russell, 1995; Schwimmer, 1997, 2002; Sampson et al, 2010)
The fossil record of dinosaurs from the portion of eastern North America that corresponds to Appalachia is poor (e.g., Weishampel and Young, 1996; Schwimmer, 1997; Weishampel, 2006), but the publication of several new taxa (e.g., Carr et al, 2005; Prieto-Márquez et al, 2016a, 2016b) and the first reports of some clades of dinosaur from this landmass (Longrich, 2016; Farke and Phillips, 2017) in the past several years have greatly increased our knowledge of the obscure fauna of the landmass
The other specimens described show much more significant wearing, such as that observed on the pedal phalanx NJSM 14682 or the smaller tooth included in NJSM 14158

Summary

Introduction

The landmass of Appalachia was created when the Western Interior Seaway flooded the interior of North America and separated the eastern portion of the continent from the west midway through the Cretaceous (Roberts and Kirschbaum, 1995; Russell, 1995; Schwimmer, 1997, 2002; Sampson et al, 2010). Other important sites include Phoebus Landing in North Carolina, which has preserved teeth and postcranial elements comparable to Dryptosaurus aquilunguis (Cope, 1866) and other tyrannosauroids, Lophorhothon, and Hadrosaurus, as well as the bones of ornithomimosaurs and the holotype of the gigantic hadrosauroid Hypsibema crassicauda (Cope, 1869) (e.g., Miller, 1967; Baird and Horner, 1979; Weishampel and Young, 1996; Schwimmer, 2016), and the Hannahatchee site of Georgia, which has preserved teeth and postcranial remains assigned to Appalachiosaurus montgomeriensis, indeterminate ornithomimosaurs, and indeterminate hadrosaurids (e.g., Schwimmer et al, 1993) These sites have been noted for their microvertebrate remains, including those of mammals, small squamates, and amphibians, making such localities extremely significant to research regarding faunal changes in North America during the Late Cretaceous (e.g., Grandstaff et al, 1992; Gallagher, 1993, 1997; Weishampel and Young, 1996; Denton et al, 2004, 2011)

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Conclusion