A new species of Saurichthys (Actinopterygii; Saurichthyiformes) from the Middle Triassic of southwestern China, with remarks on pattern of the axial skeleton of saurichthyid fishes

A new species of Saurichthys, Saurichthys yangjuanensis sp. nov. is described from the Middle Triassic (mid-Anisian) Guanling Formation of Panxian, Guizhou Province, southwestern China. This new species is different from other species of the genus in having a robust suborbital part of the maxilla; at least two supraorbitals; at least two pairs of branchiostegal rays; and a much posteriorly located anal loop that consists of at least 15 tightly stacked scales on either sides; and a peculiar pattern in ventral part of axial skeleton that consists of three types of structurally different haemal arches in terms of quantitative relationship between the haemal and neural elements per somite in anterior caudal region. The neural arches of the new species show an alternating distribution of the arch size and a prominent ridge in the arch pedicle associated with the myosepta, further confirming the double-neural arch pattern of the saurichthyiform vertebral column. The ventral part of axial skeleton in the caudal region of the new species exhibits a mixed pattern of haemal arch-like elements, which reveals a developmental and evolutionary pattern of the ventral part of the axial skeleton in Saurichthys and bridges the gap of the axial skeleton transition between the early and late Saurichthys species.