419-Million-Year-Old Fossil Reveals New Jawless Fish Species in China
- Paleontologists have described Asioaspis brachyotus, a new genus and species of polybranchiaspiform galeaspid fish that inhabited the waters of what is now southwestern China approximately 419 million years...
- Researchers recovered the fossilized remains of Asioaspis brachyotus from the Xishancun Formation near the Miandian Reservoir in Qujing, Yunnan province.
- Examination under the microscope revealed at least 12 pairs of gill pockets, though incomplete preservation prevented an exact count.
Paleontologists have described Asioaspis brachyotus, a new genus and species of polybranchiaspiform galeaspid fish that inhabited the waters of what is now southwestern China approximately 419 million years ago during the Lochkovian stage of the Early Devonian epoch.
Fossil Discovery in Yunnan Province
Researchers recovered the fossilized remains of Asioaspis brachyotus from the Xishancun Formation near the Miandian Reservoir in Qujing, Yunnan province. The collection comprises three nearly complete headshields alongside three incomplete specimens. The animal featured an oval headshield measuring roughly 4.7 to 6 cm in maximum length. This protective bone structure displayed serrated edges, a coarse granular surface, and a very broad rim on its underside.
Examination under the microscope revealed at least 12 pairs of gill pockets, though incomplete preservation prevented an exact count. Based on these diagnostic skeletal traits, the study authors assigned the species to the galeaspid order Polybranchiaspiformes. While the earliest known member of that order, Platylomaspis, dates back approximately 438.6 million years, the broader group did not experience extensive diversification until the Early Devonian period, when the Xishancun Formation produced nine genera and 15 species.
Evolutionary Transition in Seafloor Habitats
Asioaspis brachyotus exhibits a combination of primitive and advanced anatomical traits, positioning it phylogenetically between earlier and later relatives. Primitive galeaspids featured eyes and a central opening clustered closely near the top of the headshield, an adaptation suited for a semi-infaunal lifestyle partly buried in sand. In contrast, Asioaspis brachyotus possesses widely spaced openings situated near the margin of its ventral rim.
Dr. Zhi-Kun Gai, a researcher with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, and his colleagues noted that galeaspids hold fundamental importance for understanding the evolutionary origins of key gnathostome traits, including jaws, the spiracle, and paired appendages. They share a closer phylogenetic affinity with jawed vertebrates, such as humans, than with living jawless fishes like lampreys and hagfish. Regarding the new species, the authors explained that a half-buried lifestyle was physically impossible because surrounding silt and mud would pour straight into the oralobranchial chamber.
It probably lived in a normal epibenthic habit like most of galeaspids. Considering its phylogenetic position, Asioaspis brachyotus probably represents an evolutionary transition from the semi-infaunal benthic to epibenthic lifestyle within Polybranchiaspiformes.
Rui-Rui Zhang et al.