Range of motion and myology support a digging function for the forelimbs of alvarezsauroid dinosaurs

Leedham, S, Qin, Z, Griffin, BW ORCID: 0000-0001-9454-6212, Ballell, A, Yu, Y, Xu, X and Rayfield, E (2026) Range of motion and myology support a digging function for the forelimbs of alvarezsauroid dinosaurs. Proceedings of the Royal Society B Biological Sciences, 293 (2070). ISSN 0962-8452

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Abstract

Numerous lineages of theropod dinosaurs display notable modification of the forelimb, particularly reduction in size and number of digits. Alvarezsauroids are one of the most striking examples of this, exhibiting extreme shortening and increased robusticity of forelimb elements, with a functionally monodactylous manus in late-diverging taxa. These features are generally interpreted as adaptations for digging, possibly as part of a myrmecophagous ecology. Here, we test this hypothesis, using computational range of motion analysis of the shoulder and elbow joints to demonstrate the feasibility of digging behaviours in Mononykus olecranus, a highly specialized alvarezsauroid, and the less specialized Bannykus wulatensis. We find that Bannykus has the capacity for various digging styles and generalized forelimb function, while Mononykus has more restricted motion and may have employed a highly specialized digging style. We also identify similarities in forelimb muscle moment arms between alvarezsaurs and specialized mammalian diggers, supporting adaptation for digging. These findings are consistent with interpretations of insectivory in alvarezsauroids, and suggest increasing specialization to myrmecophagy throughout their evolutionary history, shedding new light on the evolution of this enigmatic clade and the ecological diversity of non-avian theropod dinosaurs.

Item Type:	Article
Uncontrolled Keywords:	alvarezsauroid; range of motion; moment arms; digging; dinosaur; convergent evolution; myrmecophagy; Muscle, Skeletal; Forelimb; Animals; Dinosaurs; Range of Motion, Articular; Fossils; Biological Evolution; Biomechanical Phenomena; alvarezsauroid; convergent evolution; digging; dinosaur; moment arms; myrmecophagy; range of motion; Dinosaurs; Animals; Range of Motion, Articular; Forelimb; Biomechanical Phenomena; Muscle, Skeletal; Fossils; Biological Evolution; 31 Biological Sciences; 3103 Ecology; 3104 Evolutionary Biology; Animals; Dinosaurs; Forelimb; Biomechanical Phenomena; Range of Motion, Articular; Muscle, Skeletal; Fossils; 06 Biological Sciences; 07 Agricultural and Veterinary Sciences; 11 Medical and Health Sciences; 30 Agricultural, veterinary and food sciences; 31 Biological sciences; 41 Environmental sciences
Subjects:	Q Science > QH Natural history > QH301 Biology Q Science > QE Geology > QE701 Paleontology
Divisions:	Biological and Environmental Sciences (from Sep 19)
Publisher:	The Royal Society
Date of acceptance:	31 March 2026
Date of first compliant Open Access:	27 May 2026
Date Deposited:	27 May 2026 10:59
Last Modified:	27 May 2026 10:59
DOI or ID number:	10.1098/rspb.2026.0565
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28670

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