Fossil Armored Fish from China Bridges Primitive and Advanced Jawless Lineages | Sci.News
Paleontologists have described a new genus and species of polybranchiaspiform galeaspid fish from the Early Devonian of Yunnan, China.
The newly described fish, named Asioaspis brachyotus, lived in what is now southwestern China approximately 419 million years ago (Lochkovian stage of the Early Devonian epoch).
The species belongs to the Galeaspida, an extinct group of bony-headed, jawless fishes found only in China and northern Vietnam.
These creatures are more closely related to jawed vertebrates, including humans, than to living jawless fishes such as lampreys and hagfish.
“Galeaspids have long been central to understanding the origin of key gnathostome traits, e.g. jaws, spiracle, and paired appendages, because they share a closer phylogenetic affinity with jawed vertebrates than extant jawless fishes,” said Dr. Zhi-Kun Gai, a researcher with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, and colleagues.
“Although restricted to China and northern Vietnam, these armored jawless fishes displayed remarkable morphological disparity and taxonomic diversity during the Siluro-Devonian, with 19 families, 74 genera, and 100 species described to date.”
“They are cladistically classified into two basal orders, Hanyangaspidiformes and Dayongaspiformes, and three major orders, Eugaleaspiformes, Polybranchiaspiformes, and Huananaspiformes.”
The fossilized material of Asioaspis brachyotus was collected from the Xishancun Formation near the Miandian Reservoir in Qujing, Yunnan province.
“The collection includes three nearly complete headshields and three incomplete headshields,” the paleontologists explained.
Asioaspis brachyotus’ oval headshield measured roughly 4.7 to 6 cm (2 inches) in maximum length.
The shield had serrated edges, a coarse granular surface and a very broad rim on its underside.
The researchers counted at least 12 pairs of gill pockets, though incomplete preservation prevented an exact count.
Based on these diagnostic features, they assigned the new species to the galeaspid order Polybranchiaspiformes.
The earliest known member of the order, Platylomaspis, dates to about 438.6 million years ago.
Yet the group did not diversify widely until the Early Devonian, when the Xishancun Formation produced nine genera and 15 species.
Asioaspis brachyotus combines features of primitive and advanced relatives, and the team’s phylogenetic analysis places it between the two.
Earlier primitive relatives had eyes and a central opening clustered near the top of the headshield, a setup suited life partly buried in sand. In the new species, those openings are widely spaced.
The scientists argue Asioaspis brachyotus could not have lived half-buried, because silt and mud would have flooded its mouth and gill chamber.
They conclude it lived on the seafloor surface, like most galeaspids, and may represent a transition between the two lifestyles.
“Asioaspis brachyotus’ median dorsal opening and paired orbital openings are not highly close-set on the top of the headshield as in Platylomaspis and Nanningaspis, but rather widely separated from each other and close to the margin of the ventral rim as in the Pentathyraspidae, Duyunolepididae, and Polybranchiaspidae,” the authors said.
“This indicates that it is impossible for Asioaspis brachyotus to have lived a half-buried lifestyle like Platylomaspis and Nanningaspis because the silt and mud would pour into the oralobranchial chamber when they were buried in sand.”
“It probably lived in a normal epibenthic habit like most of galeaspids,” they noted.
“Considering its phylogenetic position, Asioaspis brachyotus probably represents an evolutionary transition from the semi-infaunal benthic to epibenthic lifestyle within Polybranchiaspiformes.”
The discovery of Asioaspis brachyotus is reported in a paper in the journal Vertebrata PalAsiatica.
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Rui-Rui Zhang et al. 2026. Asioaspis, a new genus of Polybranchiaspiformes (Galeaspida, stem-gnathostomes) from the Lower Devonian of Yunnan, China. Vertebrata Palasiatica 64 (2): 137-150; doi: 10.19615/j.cnki.2096-9899.260113