Osteohistology of Aucasaurus garridoi (Dinosauria, Theropoda, Abelisauridae): inferences on lifestyle and growth strategy

ABSTRACT

Although osteohistology has proven to be useful to discern several palaeobiological traits and systematics in non-avian dinosaurs, the bone microstructure of several groups (e.g., abelisaurid theropods) is still poorly documented. Here, we provide a microstructural description of different bones (a cervical epipophysis, three dorsal ribs, three grastralia, and the left femur) of the type specimen of the abelisaurid Aucasaurus garridoi, its ontogenetic stage and compare its growth with other theropods, especially abelisauroid taxa. The cortical bone is mostly composed by fibrolamellar bone tissue composed of a woven-fibred matrix. Secondary remodelling varies among the different elements. The compacta of the rib shows eleven growth marks (with an additional seven in the external fundamental system), implying that the specimen was at least eleven years old and had reached somatic maturity when it died. The presence of lines of arrested growth/annuli supports a cyclical growth strategy, as in Niebla, Quilmesaurus, and Abelisauridae indet. MMCh-PV 69. All these abelisaurids indicate that the maturity based on cyclical growth marks spacing is not reliable, due to considerable variability of this parameter within a single element. This study represents the first intensive osteohistological investigation for an Abelisauridae member, providing new information on palaeobiological traits of this clade.

KEYWORDS:

• Bone microstructure
• growth strategy
• Aucasaurus
• Theropoda
• Abelisauridae

Abbreviations

CPPLIP, Centro de Pesquisas Paleontológicas L. I. Price, Universidade Federal do Triângulo Mineiro (UFTM), Peirópolis, Uberaba, Minas Gerais, Brazil; MCF-PVPH, Museo Municipal ‘Carmen Funes’ de Plaza Huincul, Plaza Huincul, Neuquén Province, Argentina; MMCh-PV, Museo Paleontológico ‘Ernesto Bachmann’, Villa El Chocón, Neuquén Province, Argentina; MPCA-PV, Museo Provincial ‘Carlos Ameghino’, Cipolletti, Río Negro Province, Argentina; MPCN-PV, Museo Patagónico de Ciencias Naturales, General Roca, Río Negro Province, Argentina; MPEF PV, Museo Paleontológico Egidio Feruglio, Trelew, Chubut Province, Argentina; ROM, Royal Ontario Museum, Toronto, Canada.

Acknowledgments

We are grateful to Museo Municipal Carmen Funes (Plaza Huincul, Neuquén, Argentina), CONICET and Universidad Nacional de Río Negro for institutional support. We thank Rodolfo Coria for allowing the access to Aucasaurus garridoi (specimen under his care). Sci-hub library and Wikipaleo group shared valuable publications for this research. Also, we thank Thomas Cullen that provided us histological data used in LAGs spacing analysis. To Novella Razzolini who assisted with the English editing. Finally, we thank the comments of the Editor-in-Chief Gareth Dyke, Martin Kundrát, and an anonymous reviewer, greatly improving the manuscript.

Disclosure statement

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