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. 2023 Jun 13:12:e83413.
doi: 10.7554/eLife.83413.

Femora from an exceptionally large population of coeval ornithomimosaurs yield evidence of sexual dimorphism in extinct theropod dinosaurs

Romain Pintore  1   2 , Raphaël Cornette  3 , Alexandra Houssaye  1 , Ronan Allain  4
Affiliations

Femora from an exceptionally large population of coeval ornithomimosaurs yield evidence of sexual dimorphism in extinct theropod dinosaurs

Romain Pintore et al. Elife. .

Abstract

Sexual dimorphism is challenging to detect among fossils due to a lack of statistical representativeness. The Angeac-Charente Lagerstätte (France) represents a remarkable 'snapshot' from a Berriasian (Early Cretaceous) ecosystem and offers a unique opportunity to study intraspecific variation among a herd of at least 61 coeval ornithomimosaurs. Herein, we investigated the hindlimb variation across the best-preserved specimens from the herd through 3D Geometric Morphometrics and Gaussian Mixture Modeling. Our results based on complete and fragmented femora evidenced a dimorphism characterized by variations in the shaft curvature and the distal epiphysis width. Since the same features vary between sexes among modern avian dinosaurs, crocodilians, and more distant amniotes, we attributed this bimodal variation to sexual dimorphism based on the extant phylogenetic bracketing approach. Documenting sexual dimorphism in fossil dinosaurs allows a better characterization and accounting of intraspecific variations, which is particularly relevant to address ongoing taxonomical and ecological questions relative to dinosaur evolution.

Keywords: 3D geometric morphometrics; dinosaurs; evolutionary biology; intraspecific variation; limb bones; sexual dimorphism.

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Conflict of interest statement

RP, RC, AH, RA No competing interests declared

Figures

Figure 1.
Figure 1.. The two first axes of the principal component analysis (PCA) for (A) complete femora and (B) distal epiphyses.
Minimal (left) and maximal (right) mean shapes per group for (C) complete femora in posterior view and (D) distal epiphyses in posterior (top) and distal (bottom) views. Abbreviations: L, lateral; P, posterior; Pr, proximal.
Figure 1—figure supplement 1.
Figure 1—figure supplement 1.. Template of (A) right complete femur of ANG10 90 and (B) mirrored left distal epiphysis of ANG14 3188 with anatomical landmarks (orange), sliding semilandmarks along curves (dark gray) and surfaces (light gray).
Figure 1—figure supplement 2.
Figure 1—figure supplement 2.. The two first axes of the principal component analysis (PCA) for proximal epiphyses of femora.
Figure 1—figure supplement 3.
Figure 1—figure supplement 3.. The two first axes of the principal component analysis (PCA) for complete tibiae.
Figure 1—figure supplement 4.
Figure 1—figure supplement 4.. Landmark configuration on the templates (A) femur; (B) tibia, with numerotation following the scheme shown in Supplementary files 4 and 5.
Figure 1—figure supplement 5.
Figure 1—figure supplement 5.. The two first axes of the principal component analysis (PCA) showing the quantification of the repeatability for the landmark configuration on femora.
Figure 1—figure supplement 6.
Figure 1—figure supplement 6.. The two first axes of the principal component analysis (PCA) showing the quantification of the repeatability for the landmark configuration on tibiae.
Figure 1—figure supplement 7.
Figure 1—figure supplement 7.. The two first axes of the principal component analysis (PCA) for the original dataset including taphonomically distorted complete femora ANG10 171 (left femur on the plot) and ANG13 2953 (right femur on the plot).
This figure highlights that the same dimorphism observed in this study is represented along PC2 when taphonomically distorted specimens are included. The taphonomically distorted specimens are located in the most negative area of the PC1 and are spread along the PC2; hence most likely interfering with the biological intraspecific variation.
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