Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods
- Published
- Accepted
- Subject Areas
- Evolutionary Studies, Paleontology, Zoology
- Keywords
- Theropoda, biomechanics, agility, phylogenetic ANCOVA, Tyrannosauridae, predation
- Copyright
- © 2018 Snively et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods. PeerJ Preprints 6:e27021v1 https://doi.org/10.7287/peerj.preprints.27021v1
Abstract
Synopsis: Tyrannosaurid dinosaurs had larger than predicted preserved leg muscle attachments and low rotational inertia relative to their body mass, indicating that they could turn more quickly than other large theropods. Methods: To compare turning capability in theropods, we regressed agility estimates against body mass, incorporating superellipse-based modeled mass, centers of mass, and rotational inertia (mass moment of inertia). Muscle force relative to body mass is a direct correlate of agility in humans, and torque gives potential angular acceleration. Agility scores therefore include rotational inertia values divided by proxies for (1) muscle force (ilium area and estimates of m. caudofemoralis longus cross-section), and (2) musculoskeletal torque. Phylogenetic ANCOVA (phylANCOVA) allow assessment of differences in agility between tyrannosaurids and non-tyrannosaurid theropods (accounting for both ontogeny and phylogeny). We applied conditional error probabilities a(p) to stringently test the null hypothesis of equal agility. Results: Tyrannosaurids consistently have agility index magnitudes twice those of allosauroids and some other theropods of equivalent mass, turning the body with both legs planted or pivoting over a stance leg. PhylANCOVA demonstrates definitively greater agilities in tyrannosaurids, and phylogeny explains nearly all covariance. Mass property results are consistent with those of other studies based on skeletal mounts, and between different figure-based methods (our main mathematical slicing procedures, lofted 3D computer models, and simplified graphical double integration). Implications: The capacity for relatively rapid turns in tyrannosaurids is ecologically intriguing in light of their monopolization of large (>400 kg), toothed dinosaurian predator niches in their habitats.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Spreadsheet for mass property calculations: Tarbosaurus bataar ZPAL MgD-I/4
This spreadsheet includes all equations necessary for calculating mass properties from lateral and coronal reconstructions. Contact author Eric Snively ([email protected]) for instructions.
Figure for digitizing Tarbosaurus bataar (ZPAL MgD I/4), after Paul (2010) and Hurum and Sabath (2003).
This image was used for digitizing outlines and calculating mass properties of Tarbosaurus bataar (ZPAL MgD I/4). The skull is tilted down in lateral view, and shortened in dorsal view to match the length. See text for details. The tail is restores as moderately wide, after Persons and Currie (2011).
Calculations of rotational inertia for body + leg
This spreadsheet has all variables and equations for calculating rotational inertia of the body and swing leg pivoting above a stance foot, for all specimens. The animal has just pushed off with its swing leg, whose center of mass is now ventrolateral to the acetabulum.
R code for replicating phylogenetic comparative results
Running the R scripts in this zip folder will enable replication of results, and modifying the code will enable execution of the methods with other questions and data.
PGLS results with both legs planted, with labeled data points
This figure is the same as text Fig. 4, but with full labels for all data points including taxa, and juvenile or adult status and specimen numbers for multi-specimen taxa.
PGLS results for pivoting on one foot, with labeled data points
This figure is the same as text Fig. 5, but with full labels for all data points including taxa, and juvenile or adult status and specimen numbers for multi-specimen taxa.