Abstract: The Placodermi is a diversified jawed vertebrate group that underwent a highly successful radiation in the Devonian period (419.2 –358.9 Ma). Recent anatomical and systematic studies, along with new fossil findings, have shown that placoderms represent an assemblage of primitive jawed vertebrates, which form the paraphyletic crownward part of the gnathostome stem group. As such, placoderms illuminate the step-wise character acquisition in the origin of crown gnathostomes or modern jawed vertebrates (including chondrichthyans, bony fishes and tetrapods). Pauropetalichthys magnoculus, an early member of petalichthyids (a subgroup of placoderms), was discovered from the late Emsian (Early Devonian) of Qujing, Yunnan, China. We investigated Pauropetalichthys using the high-resolution computed tomography (HRCT) apparatus at the Key Laboratory of Vertebrate Evolution and Human Origins, and generated the virtual reconstruction of the skull roof and neurocranium using Mimics (version 18.0). We found that Pauropetalichthys preserved part of nasal capsules which are surrounded by perichondral bones. We used to infer the shape of the neurocranium from the depression on the visceral surface of skull roof in placoderms. By means of HRCT, we can obtain the anatomical details of the neurocranium by reconstructing the preserved perichondral bones, and show for the first time the perichondral lining of the nasal capsules in petalichthyids. The research on Pauropetalichthys adds to our understanding on the morphological diversity in placoderms and helps to evaluate the interrelationships of petalichthyids.
Keywords: Petalichthyids; Placoderms; Yunnan; Devonian; HRCT; 3D reconstruction