Monday, February 15, 2021

[PaleoIchthyology • 2021] Louwoichthys pusillus • A New Stem-neopterygian Fish from the Middle Triassic (Anisian) of Yunnan, China, with A Reassessment of the Relationships of early Neopterygian Clades

Louwoichthys pusillus Xu, 2021

Neopterygii is a taxonomically diverse group of ray-finned fishes, including Teleostei, Holostei and their closely related fossil taxa. Here, a new small-sized stem-neopterygian with extraordinarily long teeth, Louwoichthys pusillus gen. et sp. nov., is described based on 14 well-preserved specimens from the Middle Triassic (Anisian) marine deposits of Yunnan, China. Louwoichthys is closely related to Luopingichthys from the same fossil beds and Ctenognathichthys from the Middle Triassic of the Monte San Giorgio area in Europe; the three genera are grouped into the family Louwoichthyidae fam. nov., which is recovered as sister to the ‘perleidiform’ Pseudobeaconiidae. Given that ‘Perleidiformes’ is notoriously paraphyletic, a new order, Louwoichthyiformes ord. nov., is introduced to group both families. The louwoichthyiform monophyly is strongly supported by a series of derived features, such as a relatively short maxilla, an anteriorly inclined preopercle, a subopercle with a prominent anteroventral extension, and two or three pairs of branchiostegal rays. Louwoichthys is one of the smallest louwoichthyiforms, having a largest standard length of 39 mm. It is deduced to be a scavenger that might use its long and sharp teeth to grasp and tear the prey from the substrate or to bite a piece from a larger prey item.

Keywords: fossil record, neopterygian, osteology, phylogeny, taxonomy

Specimen and reconstruction of Louwoichthys pusillus.
 A, IVPP V20424. B, reconstruction.


Actinopterygii Cope, 1887 
Neopterygii Regan, 1923 

Louwoichthyiformes ord. nov.

Content: Louwoichthyidae and Pseudobeaconiidae López-Arbarello & Zavattieri, 2008.

Louwoichthyidae fam. nov.

Content: Ctenognathichthys Bürgin, 1992, Luopingichthys Sun et al., 2009 and Louwoichthys.

Louwoichthys gen. nov. 

 Etymology: The generic epithet ‘Louwo’, the ancient name of Luoping County, and the Greek suffix ιχθύς, ichthys, fish. 

Geographical distribution and age: Luoping and Luxi, Yunnan, China; Pelsonian, Anisian, Middle Triassic. 

Louwoichthys pusillus sp. nov.

Etymology: The epithet is the Latin word pusillus, very little or petty, referring to the small size of the fish body.

 Holotype: IVPP V 20421, a nearly complete, laterally compressed specimen from Luoping. 

Locality and horizon: Luoping and Luxi, Yunnan, China; Second (Upper) Member of Guanling Formation, Pelsonian (~244 Mya), Anisian, Middle Triassic (Zhang et al., 2009; Huang et al., 2013). 

the phylogenetic position of Louwoichthys pusillus within the Neopterygii.

Guang-Hui Xu. 2021. A New Stem-neopterygian Fish from the Middle Triassic (Anisian) of Yunnan, China, with A Reassessment of the Relationships of early Neopterygian Clades. Zoological Journal of the Linnean Society. 191(2); 375–394. DOI: 10.1093/zoolinnean/zlaa053