New dwarf crocodylomorph from the Upper Jurassic of Portugal and the first neuroanatomical data for Atoposauridae

A new crocodylomorph fossil specimen (ML2631) from the Upper Jurassic of Lourinhã (Portugal) is described, based on a partially preserved skull table and braincase. The specimen was recovered from the Zimbral vertebrate microfossil assemblage, located in the lower part of the Praia Azul Member of the Lourinhã Formation (Kimmeridgian–Tithonian transition). The fossil was scanned using high-resolution micro-computed tomography (µCT), enabling the digital reconstruction of internal cranial structures, such as the brain cavity, cranial nerves, inner ear and paratympanic sinus system. These reconstructions represent the first neuroanatomical data ever reported for Atoposauridae, a clade of small-bodied neosuchian crocodylomorphs common in the Late Jurassic and Cretaceous of Europe. Phylogenetic analysis places ML2631 within Atoposauridae and contributes to resolving previously uncertain relationships within the group. Although fragmentary, ML2631 exhibits a unique combination of anatomical features, including a dorsolaterally open cranioquadrate passage, a sagittal crest along the frontal and parietal, a large, posteriorly placed and septate choana, large supratemporal fenestrae with a distinct posterior fossa and a squamosal lobe bearing a discontinuous lateral groove. These traits, amongst others, distinguish ML2631 from all other known atoposaurid species. Additionally, its neuroanatomical proportions suggest a dwarf adult individual with low-frequency auditory sensitivity and moderate visual acuity, consistent with a primarily terrestrial or nearshore lifestyle, coherent with the depositional environment of the fossil site. Taken together, these results highlight the taxonomic and evolutionary relevance of the specimen and underline the importance of future discoveries of more complete material to confirm its systematic and phylogenetic status within Atoposauridae.