Postcranial osteology of Manidens condorensis (Ornithischia: Heterodontosauridae) from the Lower Jurassic of Argentina: 3D reconstruction, histology, and phylogenetic implications

Abstract

Manidens condorensis, a small-bodied heterodontosaurid from the Lower Jurassic Canad ~ on Asfalto For- mation of Patagonia, represents the most complete ornithischian dinosaur currently known from South America for this interval. This study presents the first detailed description of its postcranial skeleton, based on high-resolution micro-computed tomography and 3D reconstructions of the holotype specimen (MPEF-PV 3211). We describe the first recorded proatlas in a heterodontosaurid, together with the description of vertebrae from all regions, pectoral and pelvic girdles, and preserved ribs and tendons, which offer new comparative insights into early ornithischians. Histological sections from thoracic ribs indicate a subadult ontogenetic stage and provide information on growth dynamics and tissue structure. Taphonomic analysis of the holotype, informed by disarticulation patterns and bone orientations, indicates low-energy depositional conditions and a left-side-down post-mortem resting position. Updated anatomical data were incorporated into both comprehensive and targeted phylogenetic analyses, with an emphasis on heterodontosaurid relationships. Results support the placement of Manidens as a transitional form between more basal Laurasian and more derived Gondwanan heterodontosaurids, combining plesiomorphic and specialized features, identify novel postcranial autapomorphies for Manidens, and highlight increased similarities with more complete taxa. These findings strengthen its role as a key taxon for understanding early ornithischian diversification and the evolution of herbivorous adaptations. The integration of osteology, taphonomy, histology and phylogenetics in this study significantly expands our knowledge of Manidens and its evolutionary context within Heterodontosauridae.