The evolution and diversification of growth strategies in abelisauroid theropods

ABSTRACT

Theropods comprise a successful group of mostly predatory dinosaurs with varied growth rates that colonized all continents. Much research has addressed the histology of the Global North’s Mesozoic populations, especially coelurosaurians and allosauroids. However, little has been done to understand the histological patterns of the Gondwanan populations, especially abelisauroids. Previous studies detected disparate (parallel-fibered or fibrolamellar) bone profiles between noasaurids and abelisaurids but did not include broader quantitative analyses. Here we describe the femoral histology of a mid-sized abelisaurid from the Upper Cretaceous Serra da Galga Formation, Bauru Group, Southeast Brazil. Despite the harsh semiarid paleotropical context, our specimen shows a growth rate more similar to the Patagonian abelisaurids, challenging a previous hypothesis on environmental pressure selecting taxa with lower growth rates and parallel-fibered bone tissue. We also bring data to bear from several taxa to test the hypothesis of tissue differentiation within abelisauroid clades. Our logistic regression and correlation analyses show that the variation in histology in noasaurids and abelisaurids can be explained by body size and phylogeny when considering fibrolamellar tissue, but not parallel-fibered tissue. A decrease in growth rate through the deposition of parallel-fibered bone tissue may be an example of evolutionary convergence between noasaurids and some small-bodied sauropods.

ACKNOWLEDGMENTS

We would like to acknowledge the staff of the CPPLIP, Universidade Federal do Triângulo Mineiro, especially Dr. L. Carlos Borges Ribeiro, for their fieldwork and lab assistance during the development of this project. We thank the team of the Hospital de Clínicas of the UFTM for conducting the CT scans, I. Cerda and M. Baiano, for sharing some morphometric data on Patagonian abelisaurids, G. Souza for sharing information on Vespersaurus morphometry, and the reviewers C. Griffin and V. Zurriaguz for their comments on an earlier version of this work. Thanks to C. de Ossos for funding the creation of the thin section and to I. Lemos for funding the microscope upgrade. Authors’ research grants, scholarships, and financial aid were provided by the Brazilian National Council for Scientific and Technological Development (307333/2021-3) (P.H.M.), (308900/2021-9) (T.S.M.), CONICET (A.G.M.), and UFRN “Novos Pesquisadores” (PIB21712-2023) (A.M.G.).

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

AUTHOR CONTRIBUTIONS

TSM allowed the study of the specimen. PHMF worked on the computed tomography. TA, PHMF, AGM, described the specimen. TA and AMG conducted the analyses and discussed the results.

DATA AVAILABILITY STATEMENT

The fossil is housed in a public research institution and can be accessed upon request and addressed to the collection's curator. Tomographic data and high-resolution histological photomicrographs are available in a Morphobank project linked to this article: http://morphobank.org/permalink/?4631.