The emergence of vertebrates represents one of the most significant evolutionary transitions in animal history. The earliest definitive vertebrate fossils appear in the Lower Cambrian Period (approximately 525-520 million years ago), with Myllokunmingia fengjiaoa and Haikouichthys ercaicunensis from the Chengjiang biota of China being among the oldest known specimens. These early vertebrates evolved from chordate ancestors, likely similar to modern lancelets (amphioxus). The key transition occurred through the development of neural crest cells, a mineralized skeleton, and a more complex brain. The foundation for vertebrate origins was laid in the Pre-Cambrian with early chordates like Pikaia gracilens, which exhibited basic chordate characteristics. The early Cambrian period witnessed a rapid diversification of vertebrate forms, leading to the establishment of major vertebrate lineages, including both jawless (agnathan) and later jawed (gnathostome) groups.

Deuterostomes make a sudden appearance in the fossil record during the Early Cambrian. Two deuterostome groups, the chordates and the vetulicolians, are of particular interest for understanding the evolutionary dynamics of the Cambrian evolutionary event. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document an explosive radiation of deuterostomes at the base of the Cambrian. A new vetulicolian (••• nov. gen. nov. sp.) with a polygonal anterior section and a narrow, unsegmented posterior region (‘tail’) bearing possible myotomes provides new insight into the affinities of the various body plans that emerged during the Early Cambrian. It seems clear that the advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections.