''Xiangshuiosteus wui'' is an extinct

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

brachythoraci Brachythoraci is an extinct suborder of arthrodire placoderms, armored fish most diverse during the Devonian. Phylogeny Arthrodira is divided into three main groups: the paraphyletic Actinolepida and Phlyctaenii, and then the monophyletic Br ...

arthrodire Arthrodira (Greek for "jointed neck") is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine e ...

placoderm from the Late

Emsian The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after ...

stage of the

Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, whi ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

, discovered in

Wuding County Wuding County (; Chuxiong Yi script: , IPA: ) is under the administration of the Chuxiong Yi Autonomous Prefecture, in the north-central part of Yunnan province, China, bordering Sichuan province to the north. Wuding's county seat is located ...

Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...

province, China. It has recently been reassessed as a dunkleosteid.

Etymology

The generic name literally translates as "(Pinyin:Xiāngshuǐ) + bone," but actually refers to Xiangshui Valley,Not to be confused with Xiangshui County ()(Pinyin:Xiǎng shuǐ) in

Jiangsu Jiangsu (; ; pinyin: Jiāngsū, alternatively romanized as Kiangsu or Chiangsu) is an eastern coastal province of the People's Republic of China. It is one of the leading provinces in finance, education, technology, and tourism, with its c ...

province the district in

where the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

was found. The specific name honors Wu Baosheng, the gentleman who provided the holotype to Wang Junqing, the species' describer.

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 Coccosteidae is a family of arthrodire placoderms from the Early to Late Devonian. Fossils appear in various strata in Europe, North America and China. Phylogeny Coccosteidae belongs to the larger clade Coccosteomorphi, which together with it ...

, 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 In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

Coccosteidae Coccosteidae is a family of arthrodire placoderms from the Early to Late Devonian. Fossils appear in various strata in Europe, North America and China. Phylogeny Coccosteidae belongs to the larger clade Coccosteomorphi, which together with i ...

, and represents a

transitional form A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross ...

between

and

Buchanosteidae Buchanosteidae is a family of arthrodire placoderms that lived from the Early to Middle Devonian.White, E. I. (1952). Australian arthrodires. ''Bulletin of the British Museum (Natural History) (Geology)'' 1: 249–304. Fossils appear in various ...

. A 2013 reappraisal of '' Kiangyousteus'' and several other

eubrachythoraci Eubrachythoraci is an extinct clade of arthrodire placoderms within the suborder Brachythoraci, armored fish most diverse during the Devonian. Most are considered to be pelagic (open ocean) long-distance swimmers, leading to their widespread ...

d 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

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below from the 2013 Zhu & Zhu study shows the placement of ''Xiangshuiosteus'' within

Dunkleosteidae Dunkleosteidae is an extinct family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny While members of Dunkleosteidae were pre ...

. However, the subsequent 2016 Zhu ''et al.'' study using a larger morphological dataset recovered ''Xiangshuiosteus'' well outside of

Dunkleosteoidea Dunkleosteoidea is an extinct superfamily of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator '' Dunkleosteus terrelli'' is the best known member of this group. Phylogeny Eubrachythoraci is divided into ...

and even

Eubrachythoraci Eubrachythoraci is an extinct clade of arthrodire placoderms within the suborder Brachythoraci, armored fish most diverse during the Devonian. Most are considered to be pelagic (open ocean) long-distance swimmers, leading to their widespread ...

, more in-line with Wang's original 1992

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

assessment of ''Xiangshuiosteus'', as shown in the cladogram below:

Notes

References

{{Taxonbar, from=Q13402864, from2=Q36676380 Dunkleosteidae Placoderms of Asia Paleontology in Yunnan Prehistoric animals of China Fossil taxa described in 1992

Etymology

Specimen and taxonomy

See also

Notes

References