Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousness

Abstract

Tyrannosaurids are hypothesized to be gregarious, possibly parasocial carnivores engaging in cooperative hunting and extended parental care. A tyrannosaurid (cf. Teratophoneus curriei) bonebed in the late Campanian age Kaiparowits Formation of southern Utah, nicknamed the Rainbows and Unicorns Quarry (RUQ), provides the first opportunity to investigate possible tyrannosaurid gregariousness in a taxon unique to southern Laramidia. Analyses of the site’s sedimentology, fauna, flora, stable isotopes, rare earth elements (REE), charcoal content and taphonomy suggest a complex history starting with the deaths and transport of tyrannosaurids into a peri-fluvial, low-energy lacustrine setting. Isotopic and REE analyses of the fossil material yields a relatively homogeneous signature indicating the assemblage was derived from the same source and represents a fauna living in a single ecospace. Subsequent drying of the lake and fluctuating water tables simultaneously overprinted the bones with pedogenic carbonate and structurally weakened them through wet-dry cycling. Abundant charcoal recovered from the primary bone layer indicate a low temperature fire played a role in the site history, possibly triggering an avulsion that exhumed and reburied skeletal material on the margin of a new channel with minimal transport. Possible causes of mortality and concentration of the tyrannosaurids include cyanobacterial toxicosis, fire, and flooding, the latter being the preferred hypothesis. Comparisons of the RUQ site with other North American tyrannosaur bonebeds (Dry Island-Alberta; Daspletosaurus horneri-Montana) suggest all formed through similar processes. Combined with ichnological evidence, these tyrannosaur mass-burial sites could be part of an emerging pattern throughout Laramidia reflecting innate tyrannosaurid behavior such as habitual gregariousness.

Calibrating the zenith of dinosaur diversity in the Campanian of the Western Interior Basin by CA-ID-TIMS U–Pb geochronology

“…The biogeographic analyses of Gates et al 133 based on multivariate analyses of terrestrial vertebrate taxa (including freshwater fish, reptiles/amphibians and mammals in addition to dinosaurs) added further support to a late Campanian latitudinal gradient. Rapidly growing datasets and expanded collections of the Laramidian fauna and flora 2 , 7 , 35 , 45 , 54 – 56 , 102 , 104 , 112 , 113 , 133 – 140 provide new opportunities for analyzing paleobiogeographic patterns, including biotic endemism, with increasing resolution. It has been suggested that physiographic elements such as the Elkhorn Mountains volcanic field and their impact on the adjacent alluvial systems could have generated distinct Laramidian ecosystems capable of engendering faunal divergence 141 .…”

“…began in the early 2000s and has led to many new discoveries of vertebrate, invertebrate, and plant macrofossils, including many new dinosaur species. As a result of these efforts, the fossil record of southern Utah now eclipses that of most other Cretaceous formations in North America in terms of diversity and abundance 7 , 97 – 104 .…”

Soft-Tissue, Rare Earth Element, and Molecular Analyses of Dreadnoughtus schrani, an Exceptionally Complete Titanosaur from Argentina

“…This is supported by: (1) a lack of oversteepened elemental profiles that would indicate significant, late uptake ( Figure 4 ); (2) the absence of signs of trace element leaching (i.e., most elemental concentrations increase rather than decrease toward the cortical margin; Figure 4 ), and; (3) an REE composition most similar in appearance to circum-neutral pH (cf., [ 89 ]) rivers and lake freshwaters rather than alkali groundwaters ( Figure 7 A), which is inconsistent with the incorporation of a major portion of the trace element inventory of the bone from late diagenetic fluids. Overall, the bone exhibits high surface concentrations of LREE (average ~2300 ppm; Data S1), yet its ∑REE value of 1964 ppm is comparable to that of most other Mesozoic bones reported in the prior literature ( Table 3 ), which exhibit ∑REE ranging from ~300 ppm to over 25,000 ppm [ 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 ], as are its concentrations of Y (505 ppm), Lu (4 ppm), and U (19 ppm). In contrast, Fe (0.19 wt%), Sr (1747 ppm), and Ba (447 ppm) each exhibit low average concentrations compared to other protein-bearing dinosaur bones we have recently analyzed (0.73–1.76 wt%, ~2300–3700 ppm, and ~900–2100 ppm, respectively) [ 49 , 100 ], perhaps reflecting low abundance of these elements within early diagenetic pore fluids at this site.…”

Comparative cranial biomechanics reveal that Late Cretaceous tyrannosaurids exerted relatively greater bite force than in early‐diverging tyrannosauroids

“…Teratophoneus was the only large terrestrial predator of its environment. Bonebeds of Teratophoneus specimens at different ages support the possibility of gregarious behavior in tyrannosaurids such as Albertosaurus and Daspletosaurus (Titus et al, 2021).…”