Reconstructed mass properties suggest interactions in the ecosystem of Tyrannosaurus rex

Description

Introduction/Objectives: Ecological roles and adaptations in animals relate to their mass properties (mass, centers of mass, and rotational inertia), which influence ecologically critical aspects of lifestyle including speed, agility, life history, and thermoregulation. While this is informative for an individual animal’s potential performance, investigating mass properties of multiple taxa within the same ecosystem allows for comparisons pertinent to interspecific interactions, such as those between predators and prey. The objective of this study is reconstruct anatomy and rotational inertia of large dinosaurs from the end their reign in western North America, so that we can make inferences about these interactions.

Methods: We used ZBrush 2023 to sculpt life restorations of 9 non-avian dinosaur taxa from the late Maastrichtian of northern Laramidia, restoring soft tissue anatomy using skeletal diagrams and examination of mounted skeletons, as well as digitized 3-dimensional skeletons where available. These models were then split into axial body and whole-body models. We also reconstructed the negative space created by the respiratory system, including the trachea, lungs, and air sacs in the case of theropods, and used MeshMixer to subtract the respiratory space from the models. The resulting models were imported into MeshLab, where we calculated mass and rotational inertia for both whole and axial bodies.

Results: Our sample of dinosaur taxa broke down into four categories of body mass, rotational inertia ranges, and proximate likelihood of interaction. (1) All adult taxa with body mass <300kg, had rotational inertias (RI) <100kg*m²; (2) adults of body mass ranging from 300-1000kg had RI from 100-1000kg*m², (2) subadults of taxa from the final category, between 1000-5000kg in body mass, had RI between 1000-10,000kg*m²; (4) taxa with body masses greater than 5000kg and rotational inertia higher than 10,000kg*m². Triceratops has lower rotational inertia than Tyrannosaurus rex of similar body mass, though Edmontosaurus and Tyrannosaurus rex converge in rotational inertia values at large body sizes, while Struthiomimus, Dakotaraptor, and Pachycephalosaurus all converge in rotational inertia values with those estimated for a juvenile Tyrannosaurus rex.

Conclusions: These results show that the largest dinosaurs of the late Maastrichtian of northwestern North America segregated into their own bin of mass properties relative to other members of their ecosystem. This may indicate an ecological class, with adults of these taxa interacting more often with each other than with adults of other taxa. The differences in rotational inertia between Triceratops, Edmontosaurus annectens, and Tyrannosaurus rex suggest hypotheses of differing predation tactics by the latter and predator deterrence by the former. The mass properties obtained in this study will enable testing of hypotheses including musculoskeletal torque to estimate angular and linear accelerations, and further comparative data from extant animals and ecosystems will test parameters important for inferred predation strategies.

Period	15 Feb 2024
Event title	Oklahoma State University Center for Health Sciences Research Week 2024
Event type	Conference
Location	Tulsa, United States, OklahomaShow on map
Degree of Recognition	Regional