The circulatory system of Galeaspida (Vertebrata; stem-Gnathostomata) revealed by synchrotron X-ray tomographic microscopy

Micro-CT provides a means of nondestructively investigating the internal structure of organisms with high spatial resolution and it has been applied to address a number of palaeontological problems that would be undesirable by destructive means. This approach has been applied successfully to characterize the cranial anatomy of Shuyu, a 428 million-year-old galeaspid (jawless stem-gnathostome) from the Silurian of Changxing, Zhejiang Province, China. Here, we use the synchrotron X-ray tomographic microscopy (SRXTM) to further describe the circulatory system of the head of Shuyu. Our results indicate that the circulatory system of galeaspids exhibits a mosaic of primitive vertebrate and derived gnathostome characters, including a number of derived gnathostome characters that are absent from osteostracans - the group conventionally interpreted as the sister lineage of jawed vertebrates. Our study provides a rich source of information that can be used to infer and reconstruct the early evolutionary history of the vertebrate cardiovascular system. Crown Copyright (C) 2019 Published by Elsevier B.V. All rights reserved.