A new species of Saurichthys from the Middle Triassic (Anisian) of southwestern China

摘要: The saurichthyiform fishes were effective predators and hence the significant consumers in the aquatic ecosystems during the Early Mesozoic. They showed a notable diversification in the Anisian (Middle Triassic) Lagerst鋞ten of southwestern China. In this contribution, we report a new species of Saurichthys from the Anisian of Yunnan, China, that displays some peculiar modifications of the axial skeleton and the longate body of the group. This new species, Saurichthys spinosa is a small-sized saurichthyid fish characterized by a very narrow interorbital region of the skull roof, an anteriorly expansive and ventrally arched cleithrum, proportionally large abdominal vertebrae lacking neural spines and alternately bearing laterally-stretching paraneural plates, few fin rays in the median fins, and two paralleling rows of needle-like flank scales with strong thorns. This fish has slimmed down the body by reducing the depth of the head and the epaxial part of the trunk. The elongate paraneural plates inserted in the horizontal septum and the rigid interlocking of the flank scales render the fish a very stiff body, which is compatible with the functional consequence of the obvious decrease of the body (vertebral) segments. This discovery reveals the variability of the axial skeleton and the hydrodynamic properties of the saurichthyiform fishes. These factors, together with the innovations in the locomotion and feeding habit, might have intrinsically effected the evolutionary burst of the eastern Tethyan saurichthyiform fishes during the Anisian, a marked signature of the rapid radiation stage of the biotic recovery after the end-Permian extinction.