Authors: CAVIN, LIONEL¹; SUTEETHORN, VARAVUDH²

Source: Palaeontology, Volume 49, Number 2, March 2006 , pp. 339-353(15)

Publisher: Wiley-Blackwell

Abstract:

: 

A new semionotiform fish, Isanichthys palustris gen. et sp. nov., is described from the Late Jurassic – Early Cretaceous Phu Kradung Formation, north-east Thailand. I. palustris is known from a single, nearly complete specimen found alongside abundant Lepidotes specimens at the Phu Nam Jun locality. I. palustris shows a mixture of semionotid-like characters, such as the pattern of cheek ossifications, and lepisosteid-like characters, such as the body shape and a dorsal fin opposed by an anal fin. I. palustris possesses only some of the characters currently used to define the Semionotidae. Cladistic analyses including various semionotid and gar taxa, together with Amia calva and Leptolepis coryphaenoides, suggest that the Semionotiformes (Lepisosteidae and `Semionotidae') form a monophyletic clade, but the `Semionotidae' taxa form an unresolved polytomy. The relationships between Semionotiformes, Halecomorphi and Teleostei are unresolved. When restricted to the best-known taxa, however, the analysis shows the monophyly of the Semionotidae sensu stricto (Semionotus + Lepidotes) and a sister-group relationship between halecomorphs and teleosts. These last two results are regarded as the preferred hypothesis for further studies. I. palustris is the only known example of a predaceous, probably piscivorous, `semionotid'. It illustrates the great diversity and ecological adaptation of the semionotiforms during the Late Jurassic – Early Cretaceous. We question the phylogenetic relationships of `ancient fishes' founded on molecular-based trees because we suspect that the use of very few Recent taxa as representatives of previously diverse lineages is an inevitable, but important, bias in the construction of such trees.

Keywords: Actinopterygii; Semionotiformes; Lepisosteidae; new taxon; Thailand; Mesozoic; phylogeny

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1475-4983.2006.00539.x

Affiliations: 1: Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; current address: Department of Geology and Palaeontology, Muséum d'Histoire naturelle, CP6434, 1211 Genève 6, Switzerland;, Email: lionel.cavin@mhn.ville-ge.ch 2: Geological Survey Division, Department of Mineral Resource, Rama VI Road, Bangkok 10400, Thailand

Publication date: 2006-03-01

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