Mandibular force profiles and tooth morphology in growth series of Albertosaurus sarcophagus and Gorgosaurus libratus (Tyrannosauridae: Albertosaurinae) provide evidence for an ontogenetic dietary shift in tyrannosaurids¹

Abstract

The albertosaurines Albertosaurus sarcophagus and Gorgosaurus libratus are among the best represented tyrannosaurids, known from nearly complete growth series. These specimens provide an opportunity to study mandibular biomechanical properties and tooth morphology in order to infer changes in feeding behavior and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the middentary region, indicating that the anterior extremity of the jaws played an important role in prey capture and handling through ontogeny. The symphyseal region was better adapted to withstand torsional stresses than in most non-avian theropods, but not to the extent seen in Tyrannosaurus rex, suggesting that albertosaurine feeding behavior may have involved less bone crushing or perhaps relatively smaller prey than in T. rex. The constancy of these biomechanical properties at all known growth stages indicates that although albertosaurines maintained a similar feeding strategy through ontogeny, prey size/type had to change between juvenile and mature individuals. This ontogenetic dietary shift likely happened when individuals reached a mandibular length of ~58 cm, a size at which teeth shift from ziphodont to incrassate in shape and bite force begins to increase exponentially. The fact that large albertosaurines were capable of generating bite forces equivalent to similar-sized tyrannosaurines suggests that no significant differences in jaw closing musculature existed between the two clades and that the powerful bite of T. rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.

Macroevolutionary trends in theropod dinosaur feeding mechanics

“…Our results add to these studies by showing that later-diverging caenagnathids have some of the most speedefficient mandibles among oviraptorosaurians (Figure S2), which could have been an adaptation for prey capture. As in carnivorous theropods, 57 body size might also be a factor affecting feeding mechanics: exceptionally large herbivorous theropods like Deinocheirus and Gigantoraptor display stress/strain distribution patterns that are unlike other members in the same clade (Figures 1 and S1), which supports hypotheses that they were specialized feeders. 10,21,58 The presence of large-bodied members in every herbivorous theropod clade 9 suggests that size-related niche partitioning might have been widespread among them.…”

Theropod guild structure and the tyrannosaurid niche assimilation hypothesis: implications for predatory dinosaur macroecology and ontogeny in later Late Cretaceous Asiamerica1

“…This transition occurred sometime after the Turonian (Zanno and Makovicky 2013;Zanno et al 2019;Nesbitt et al 2019) and before the middle Campanian (Loewen et al 2013) in North America. A similar pattern is observed in Asia, where the tyrannosauroid Timurlengia of the Turonian Bissekty Formation is a mid-sized predator , while a larger carcharodontosaurid has recently been reported from the same unit (Tanaka et al 2020). The slightly stratigraphically younger Turonian-Santonian Upper Bayan Shireh Formation of Mongolia and Santonian Iren Dabasu Formation of Inner Mongolia (Averianov and Sues 2012) lack evidence at present of carcharodontosaurids, although in the former the large dromaeosaurid Achillobator rivals the sympatric tyrannosauroid cf.…”

The stability of dinosaur communities before the Cretaceous–Paleogene (K–Pg) boundary: A perspective from southern Alberta using calcium isotopes as a dietary proxy

“…In the three uppermost Cretaceous sedimentary formations of Alberta, Canada, dinosaur enamel δ 44/42 Ca values display systematic, diet-related inter-taxon differences and provide encouragement for the study of isotopic variability at the individual scale to evaluate ecological behaviors linked to spatial or seasonal variations in diet or habitat partitioning (Fricke and Pearson, 2008), mobility (Terrill et al, 2020), and ontogenetic dietary shifts (Woodward et al, 2020;Therrien et al, 2021). With Ca isotope procedures allowing high-precision and high-resolution sampling, such questions may easily be investigated using this method.…”