Sunday, 1 September 2013

An Ichthyodectiform Fish from the Early Cretaceous of Queensland, Australia.

Ichthyodectiforms were large, predatory Fish from the Late Jurassic and Cretaceous, distantly related to modern Mooneyes, Elephantfish, Featherbacks, Arowanas and Butterflyfish. The typically reached between one and five meters in length, though some species exceeded six meters. Unlike their modern relatives, which are found in freshwater in Africa, Australia, South America and parts of Asia, the Ichthyodectiforms were predominantly marine, though several of their modern relatives still grow very large, including the Arapaima (Arapaima gigas), a South American freshwater species which sometimes grows over 2.5 m in length.

In a forthcoming paper in the journal Acta Palaeontologica Polonica available online since 17 June 2013, Rodney Berrell or the School of Biological Sciences at The University of Queensland, Jesús Alvarado-Ortega of the Departamento de Paleontología at the Instituto de Geología at the Universidad Nacional Autónoma de MéxicoYoshitaka Yabumoto of the Kitakyushu Museum of Natural History and Human History and Steven Salisbury, also of the School of Biological Sciences at The University of Queensland, describe a new species of Ichthyodectiform Fish from the Early Cretaceous of Queensland.

The new species is placed in the genus Cladocyclus, which has previously been described from the Cretaceous of Brazil and Morocco, and given the specific name Cladocyclus geddesi, in honour of Kerry Geddes, who discovered the fossil specimen from which the species is described during a University of Queensland expedition to Isisford, central-western Queensland, in 2005. It was preserved in a sandstone nodule derived from the Winton Formation, which outcrops across a large area of western Queensland, northeastern South Australia and north-western New South Wales, and which is interpreted as having been laid down in a freshwater fluvial-lacustrine environment deposited on a broad coastal plain as the epicontinental Eromanga Sea withdrew, between 103 and 93.9 million years ago.

Cladocyclus geddesi in lateral view. Photograph (A) and interpretive drawing (B). Abbreviations: ang, angular; bsc, basal sclerotic bone; cl, cleithrum; cor, coracoid; den, dentary; epi, epioccipital bone; epn, epineural; gr, gill rakers; hym, hyomandibular; io1- 4, infraorbital bones (numbered anterior to posterior); iop, interopercle; mpa, mesoparietal (= fused parietals); mx, maxilla; pcl, postcleithrum; pmx, premaxilla; pop, preopercle; rode, rostrodermethmoid bone; sma, supramaxilla anterior; smp, supramaxilla posterior; soc, supraoccipital; sop, subopercle; stt, supratemporal. Berrell et al. (2013).

The species is described from the skull, pectoral girdle and first 19 vertebrae of a Fish preserved as part and counterpart on a split sandstone nodule. The specimen being approximately 270 mm in length, and the living fish is estimated to have been 600-1050 mm long.

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