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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

Publication: Canadian Journal of Earth Sciences
26 January 2021

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 to infer changes in feeding behaviour and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the mid-dentary 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 behaviour may have involved less bone crushing or perhaps relatively smaller prey than in Tyrannosaurus 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 Tyrannosaurus rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.

Graphical Abstract

Résumé

Les albertosaurinés Albertosaurus sarcophagus et Gorgosaurus libratus figurent parmi les tyrannosauridés les mieux représentés, les connaissances à leur sujet reposant sur des séries de croissance quasi complètes. Ces spécimens offrent l’occasion d’étudier les propriétés biomécaniques des mandibules et la morphologie des dents pour en inférer des changements du mode d’alimentation et de la force de morsure au fil de l’ontogenèse chez les tyrannosauridés. Des profils de force des mandibules révèlent que la région symphysaire des albertosaurinés est toujours plus résistante en flexion que la région dentaire médiane, ce qui indique que l’extrémité antérieure des mâchoires jouait un important rôle dans la capture et la manipulation des proies tout au long de l’ontogenèse. La région symphysaire des albertosaurinés était mieux adaptée à résister aux contraintes en torsion que celle de la plupart des théropodes non aviaires, mais pas autant que celle de Tyrannosaurus rex, ce qui indiquerait que le broyage d’os était possiblement un aspect moins important de leur comportement d’alimentation ou que leurs proies étaient plus petites que celles de Tyrannosaurus rex. La constance de ces propriétés biomécaniques à toutes les étapes connues de la croissance indique que, bien que la stratégie d’alimentation des albertosaurinés ne variait pas beaucoup au fil de l’ontogenèse, la taille et le type de proies acquises devaient changer entre les individus juvéniles et matures. Cette transition ontogénétique de l’alimentation se produisait vraisemblablement lorsque les individus atteignaient une longueur des mandibules de ∼58 cm, taille à laquelle la forme des dents passe de ziphodonte à épaissie et la force de morsure commence à augmenter de façon exponentielle. Le fait que les grands albertosaurinés étaient capables de produire des forces de morsure équivalentes à celles de tyrannosaurinés de même taille donne à penser qu’il n’y avait aucune différence significative de la musculature de fermeture des mâchoires entre les deux clades et que la puissante morsure de Tyrannosaurus rex est le résultat de sa grande taille plutôt que d’adaptations singulières reliées à une spécialisation écologique. [Traduit par la Rédaction]

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cover image Canadian Journal of Earth Sciences
Canadian Journal of Earth Sciences
Volume 58Number 9September 2021
Pages: 812 - 828

History

Received: 15 September 2020
Accepted: 12 January 2021
Accepted manuscript online: 26 January 2021
Version of record online: 26 January 2021

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Key Words

  1. feeding behaviour
  2. paleoecology
  3. biomechanics
  4. mandibular force profile
  5. Tyrannosauridae
  6. diet

Mots-clés

  1. mode d’alimentation
  2. paléoécologie
  3. biomécanique
  4. profil de force des mandibules
  5. tyrannosauridé
  6. régime alimentaire

Authors

Affiliations

François Therrien [email protected]
Royal Tyrrell Museum of Palaeontology, P.O. Box 7500, Drumheller, AB T0J 0Y0, Canada.
Darla K. Zelenitsky
Department of Geoscience, University of Calgary, Calgary, AB T2N 1N4, Canada.
Jared T. Voris
Department of Geoscience, University of Calgary, Calgary, AB T2N 1N4, Canada.
Kohei Tanaka
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.

Notes

1
This paper is part of a series of invited papers in honour of palaeontologist Dr. Dale Alan Russell (1937–2019).
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from copyright.com.

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