Niche Partitioning in Theropod Dinosaurs: Diet and Habitat Preference in Predators from the Uppermost Cedar Mountain Formation (Utah, U.S.A.)

Abstract

We explore hypothetical ecologies to explain diversity among predatory dinosaurs in North America’s medial Cretaceous, based on occurrence, tooth morphology, and stable isotope analysis. The Mussentuchit local fauna, Utah, USA, is among the best-known terrestrial vertebrate assemblages from the Cretaceous. Study samples include teeth from six microvertebrate sites, ranging in depositional setting from distal floodplain to channel lags. We recognize four theropod morphotypes: a comparatively large theropod (morph 1), a medium-sized dromaeosaurid (morph 2), a small dromaeosaurid (morph 3), and a tooth-morph similar to the genus Richardoestesia (morph 4). These four morphotypes vary significantly in mean size, from 15.1 mm in the largest theropod to 3.7 mm in Richardoestesia. Further, tooth representation from two of the best-sampled microsites (representing a channel/splay and floodplain deposit) show differing patterns of abundances with morphs 1 and 3 having roughly the same abundance in both sites, while morph 2 was more abundant in the floodplain setting and morph 4 was more abundant in the channel/splay. Stable isotope analysis (δ13C; δ18O) of tooth carbonate from the theropod morphotypes, goniopholidid crocodilians, and matrix (to test for diagenesis) from these sites were also analyzed. The theropods show modest differences in δ13C values between each other, with carbonate from the teeth of morphs 1, 3, and 4 being enriched in 13C for the channel/splay relative to the floodplain environments, possibly indicative of dietary plasticity in these species. We hypothesize that these data indicate that the Mussentuchit theropods had different niches within the predator guild, suggesting plausible means by which ecospace was divided among the predatory dinosaurs of the Mussentuchit local fauna.

Skeletal completeness of the non‐avian theropod dinosaur fossil record

“…; Frederickson et al . ). A drop in sauropod diversity across the Jurassic–Cretaceous boundary (Mannion et al .…”

“…; Lautenschlager ; Frederickson et al . ), and exhibit high taxonomic diversity, morphological disparity (Brusatte et al . , b; Griffin & Nesbitt ; Barta et al .…”

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

“…Teeth, and particularly tooth enamel, are robust skeletal elements (Hillson, 2005), and most toothed theropods had 50 or more teeth that were replaced every one to two years (Fiorillo and Currie, 1994;Erickson, 1996). Consequently, theropod teeth are one of the most common fossils in terrestrial Mesozoic formations (e.g., Erickson, 1996;Smith et al, 2005;Blob and Badgley, 2007) and are constantly reported in the literature (e.g., Currie et al, 1990;Rauhut and Werner, 1995;Baszio, 1997;Zinke, 1998;Sankey et al, 2002;Sweetman, 2004;Maganuco et al, 2005;Vullo et al, 2007;Larson, 2008;Casal et al, 2009;Lubbe et al, 2009;Ősi et al, 2010;Han et al, 2011;Sues and Averianov, 2013;Larson and Currie, 2013;Richter et al, 2013;Torices et al, 2015;Kear et al, 2013;Madzia, 2014;Hendrickx and Mateus, 2014a;Cobos et al, 2014;Tavares et al, 2014;Fanti et al, 2014;Brusatte and Clark, 2015;Csiki-Sava et al, 2016;Gerke and Wings, 2016;Alonso et al, 2017;Malafaia et al, 2017a;Avrahami et al, 2018;Frederickson et al, 2018;…”

“…Isolated theropod teeth provide taphonomic, paleoenvironmental and paleoecological data (e.g., Briggs and Crowther, 2001;Amiot et al, 2004Amiot et al, , 2006Amiot et al, , 2009Amiot et al, , 2011Rogers et al, 2007;Fanti et al, 2014;Gerke and Wings, 2016;Hassler et al, 2018;Frederickson et al, 2018). They may also provide evidence for paleodiversity, biostratigraphy (i.e., temporal/geographic ranges of theropod taxa), and anatomical information on clades when articulated skeletal fossils are missing or poorly represented Larson et al, 2016).…”

Rise and fall of †Pycnodontiformes: Diversity, competition and extinction of a successful fish clade

“…Characters, which are assumed to have diverged in the past (Hector & Hooper, 2002), thus are crucial to identify niche overlap and related competition patterns but also postcompetitive (realized) ecological niche differentiation. While niche partitioning patterns are generally well documented for modern vertebrates, identifying niche partitioning patterns in extinct vertebrates is challenging (Frederickson et al., 2018), also because even extreme morphological character divergences might not prove competition in the past (Zaret & Rand, 1971). Ecological variation nevertheless generally is assumed being reflected in abundant morphological specializations.…”