An exquisitely preserved young iguanodontian from the Upper Jurassic of Tanzania sheds light on skeletal fusion patterns within Archosauria

Dysalotosaurus lettowvorbecki (Ornithopoda, Dinosauria) is a small-sized dryosaurid iguanodontian known from various isolated remains collected from the Tendaguru Formation (Upper Jurassic, Tanzania). Micro-computed tomography of a small individual encased in a block offered a unique opportunity to describe c. 40 associated elements and clarify previously undocumented anatomical details of this species. The preserved material includes cranial elements, an almost complete cervical series, four dorsal vertebrae, and part of the appendicular skeleton. A comprehensive assessment of the individual, based on qualitative features and morphometric analyses, indicates an early ontogenetic stage and an absolute age of 4-5 years. Notably, the cervical vertebrae predominantly exhibit partially closed neurocentral sutures, whereas the two more posterior dorsal vertebrae have open sutures, along with disarticulated neural arches. This finding challenges the simple 'tail-to-head' fusion pattern typically assumed for the vertebral series of Ornithopoda, and suggests a potential cervical locus of neurocentral fusion within this clade. Phylogenetic comparative methods indicate a complex distribution of these neurocentral fusion patterns within Archosauria.