Here we report the discovery of extensive endochondral bone in a new genus of ‘placoderm’-like fish from the Early Devonian (Pragian) of western Mongolia described using x-ray computed microtomography (XR-μCT). Alternatively, use our A–Z index 65 66 Description 67 MPC-FH100/9.1 consists of a partial braincase and skull … The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation (Frasnian, Upper Devonian), Québec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone … Considering the evolutionary losses of membrane and perichondral bone in chondrichthyans, endochondral bone might have undergone similar loss resulting from the same genetic basis (i.e. absence of any SCPP genes). Among other bone types found in early vertebrates are perichondral bone (a thinly laminated acellular bone) and endochondral bone. Search type Research Explorer Website Staff directory. The articular surfaces for the palatoquadrate, which are located anteriorly on the suborbital-ethmoidal shelf close to the premedian plate (pq, The scan reveals a characteristically placoderm architecture for the endoskeleton, with a well-developed perichondral bone envelope but no trace of endochondral ossification. However, its endochondral space is filled with an extensive network of fine trabeculae resembling the endochondral bone of osteichthyans. The fossil consists of a partial skull roof and braincase with anatomical details providing strong evidence of placement in the gnathostome stem group. These results provide direct support for theories of generalised bone loss in chondrichthyans. Here we report the discovery of extensive endochondral bone in Minjinia turgenensis , a new genus and species of ‘placoderm’-like fish from the Early Devonian (Pragian) of western Mongolia described using x-ray computed microtomography (XR-µCT). Perichondral bone is often found surrounding soft tissue that passes through cartilage, as can be found in placoderms with cartilage braincases where the nerves and arteries passing through the braincase wall can have perichondral bone surrounding them. However, its endochondral … Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation ( Frasnian, Upper Devonian), Quebec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. Although extensive endochondral bone is exclusively found in osteichthyans, the paleontological data show that incipient endochondral bone is probably present in some placoderms such as petalichthyids and arthodires. ### Competing Interest Statement ‘placoderm’-grade stem gnathostome with endochondral bone, deep epaxial 62 muscle cavities flanking a slender occipital ridge, and the following possible autapomorphies: 63 dermal bones covered in sparsely placed tubercles, penultimate spino-occipital nerve canal 64 substantially larger in diameter than others. Chondrichthyans (sharks and their kin) are the living sister group of osteichthyans and have cartilaginous endoskeletons, long considered the ancestral condition for all jawed vertebrates (gnathostomes). The resultant structure mimics that of osteichthyan endochondral bone. Endochondral bone is the main internal skeletal tissue of nearly all osteichthyans—the group comprising more than 60,000 living species of bony fishes and tetrapods. Further investigation on hard tissues in placoderms … The absence of bone in modern jawless fishes and the absence of endochondral ossification in early fossil gnathostomes appears to lend support to this conclusion. The fossil consists of a partial skull roof and braincase with anatomical details providing strong evidence of placement in the gnathostome stem group. Here we report the discovery of extensive endochondral bone in Minjinia turgenensis , a new genus and species of ‘placoderm’-like fish from the Early Devonian (Pragian) of western Mongolia described using x-ray computed microtomography (XR-µCT).