Monday 23 April 2012

An early Ray-Finned fish from the Middle Triassic Luoping Biota of Yunnan Province, China.

Neopterygian (Ray-Finned) Fish first appeared in the Late Permian, and became the most abundant group of fish during the Mesozoic; they remain such today. Neopterygians cane be divided into three groups, the Teleosts, fish with expandable mouthparts, which are the most abundant fish today, and two other groups, the Semiontids (which include the modern Gars) and Halecomorphs (which include the modern Bowfin), which were abundant during the Mesozoic but are now represented by only a few species. The relationships of the early Neoptergyians are unclear, but the Semiontids and Halecomorphs are generally thought to be more closely related to each other than either is to the Teleosts; together they are collectively referred to as Holosteians.

A fisherman with an Alligator Gar, Atractosteus spatula, one of North America's largest fish and a surviving Semiontid Fish. The Megafishes Project.

In a paper in the April edition of the journal Acta Palaeonotologica Polonica a team of palaeontologists led by Wen Wen of the Chengdu Institute of Geology and Mineral Resources announce the discovery of an early Neopterygian Fish that does not fit clearly into any of these groups, and the implications of this.

The new species is named as Luoxiongichthys hyperdorsalis, meaning 'The humpbacked fish from Luoxing'. It has a distinctive forward curving hump on its back that Wen Wen et al. compare to a 'reverse shark’s dorsal fin'. This is unlikely to have been advantageous to the fish when swimming, and was probably used for display.

Luoxiongichthys hyperdorsalis. Top, photograph of original specimen. Middle, interpretive drawing based upon photograph. Bottom, reconstruction of living fish. From Wen Wen et al. (2012).

Luoxiongichthys hyperdorsalis was described from a single specimen found in the Daaozi Section of the Guanling Formation, at Daaozi Village in Luoping County, about 25 km northeast of the town of Luoxiong. This is a muddy limestone that has produced a large number of excellently preserved vertebrates, invertebrates and plants from the Middle Triassic, collectively refered to as the Luoping Biota.

The location of the section that produces the Luoping Biota. From Wen Wen et al. (2012).

Luoxiongichthys hyperdorsalis does not fit easily into any group of Neopterygian Fish, but appears to be more closely related to the Semiontids and Halecomorphs than to the Teleosts, supporting the theory that these groups are related, and probably more closely related to the the Semiontids than to the Halecomorphs. Several early Semiontids have also been shown to have humped backs, supporting this relationship.

Diagram showing the probable relationships of Luoxiongichthys hyperdorsalis to other groups of fish. From Wen Wen et al. (2012).

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