Abstract:

This paper is the first to report the discovery of a well-preserved Ordovician fish-like animal fossil with a reliable shield armor structure. The vertebrate fossil was collected from purplish-red sandy-limestone outcrops of coast-shallow marine facies that are part of the Upper Ordovician Qarbake Formation in the Yijianfang section, Bachu county, Xinjiang. The new genus and species has been denoted Haoina elegantia Guo & Wang as per the system of binomial nomenclature, and a new family (Haoinaspididae) and order (Haoinaspidiformes) have also been described based on the unique biological features of this species. The new genus describes an ostraeoderm, while the Qarbake Formation can be constrained to the Sandbian stage based on the conodont fossil zone. The fossil of the new fish-like animal preserves its dorsal shield armor and shows that the dorsal shield on its head is covered with ridges composed of complex tumors on the derma. The ridges can be subdivided into four types: The orbit openings are situated at the dorsal-front edge of the head shield with wide and deep orbit hollows. The pineal area is located at either side of the orbits. And the well-developed sensory canal system in the armor of the head shield shows the tube system texture of corium and subcutaneous tissues. Based on comparisons with the vertebrate biogeographic regions of other fossils, we suggest the establishment of a new fish-like animal typified in a proto-Tethys Ordovician Haoniaspid-Bachuiaspid vertebrate biogeographic province. This fossil is the oldest fish-like animal with a reliable exoskeleton found in China or even in Asia.

Key words: Ordovician, fish-like animal, Ostracodermi, Haoina, Xinjiang