Xiangshuiosteus in Yunnan

Xiangshuiosteus wui is a brachythoracid arthrodire placoderm from the Late Emsian epoch of Wuding, Yunnan. It has recently been reassessed as a dunkleosteid.

Specimen and taxonomy

X. wui is known from a flattened, “Buddhist cap” shaped skull roof. The skull roof is strongly reminiscent of those of coccosteids, but also has anatomical features otherwise diagnostic of buchanosteids. This mix of anatomy lead its describer, Wang Junqing, to suggest that X. wui is the sister taxon of Coccosteidae, and represents a transitional form between Coccosteidae and Buchanosteidae. A reappraisal of Kiangyousteus and several other eubrachythoracid arthrodire genera by You-An Zhu and Min Zhu lead to the conclusion that X. wui not only does not represent a transitional form between coccosteids and buchanosteids, but is actually a dunkleosteid closely related to the Gogo Reef Eastmanosteus calliaspis (which is, in turn, implied to be not of the genus Eastmanosteus).


The generic name literally translates as “Chinese: 香水; literally: ‘perfume'(Pinyin:Xiāngshuǐ) + bone,” but actually refers to Xiangshui Valley, the district in Wuding County where the holotype was found. The specific name honors Wu Baosheng, the gentleman who provided the holotype to Wang Junqing, the species’ describer.

Discovery and Naming

  • Initial Discovery: Fossils of Xiangshuiosteus were discovered in the Devonian-aged rock formations in Yunnan Province, China.
  • Name Origin: The genus name “Xiangshuiosteus” is derived from “Xiangshui,” referring to the region where the fossils were found, and “osteus,” meaning bone in Greek.

Physical Characteristics

  • Anatomy: As an arthrodire placoderm, Xiangshuiosteus had a heavily armored head and thorax, with a more flexible, unarmored body. Its jaws were equipped with bony plates that functioned as teeth.
  • Size: The exact size of Xiangshuiosteus is not well-documented, but typical arthrodires varied from small to medium-sized fish, with some reaching several meters in length.


  • Arthrodire Placoderm: Xiangshuiosteus belongs to the arthrodire order of placoderms, which were among the dominant vertebrates during the Devonian period. Arthrodires are characterized by their jointed bony armor covering the head and thorax.


  • Habitat: During the Devonian period, Yunnan was part of a marine environment rich in biodiversity. Xiangshuiosteus would have lived in these ancient seas, alongside other placoderms, early bony fish, and various invertebrates.
  • Contemporary Fauna: Xiangshuiosteus shared its habitat with other marine life forms typical of the Devonian period, including various other placoderms, acanthodians (spiny sharks), and early actinopterygians (ray-finned fish).


  • Evolutionary Importance: The discovery of Xiangshuiosteus contributes to our understanding of the diversity and distribution of arthrodire placoderms during the Devonian period. It provides insights into the evolutionary history of early jawed vertebrates.
  • Fossil Record in Yunnan: The fossil record in Yunnan, including finds like Xiangshuiosteus, highlights the region’s significance as a site for Devonian marine life. These fossils help paleontologists piece together the ancient ecosystems that existed in what is now southwestern China.

Xiangshuiosteus is an important genus for studying the evolution of early jawed vertebrates and the biodiversity of the Devonian seas. Its fossils in Yunnan contribute to the rich paleontological heritage of the region.