Abstract
A single specimen of a new acanthomorph fish is described from a Turonian locality sampling the northern part of the Cretaceous Western Interior Seaway. This brings to three the number of acanthomorphs from Lac des Bois, Northwest Territories, Canada. The previously named acanthomorph, Boreiohydrias dayi (Boriohydriidae), was placed in the Polymixiiformes. The second, represented by a poorly preserved fish, was left unnamed and incertae sedis in Acanthomorpha. The new one described here, Cumbaaichthys oxyrhynchus gen. et sp. nov. cannot be easily placed in any previously described families. This fish is placed in the Polymixiiformes based on the caudal skeleton having 18 principal rays (16 branched), and having a full neural spine on the second preural centrum. Polymixiiform relationships are not well established but they are the subject of several current studies; therefore, the new acanthomorph is placed incertae sedis within this order but with the understanding that this placement may be refined with future work. Previous studies have suggested that acanthomorphs may have flourished with warming climates of the Cenomanian–Turonian. A comprehensive survey of named acanthomorphs from mid-Cretaceous deposits shows there are more species known from the Cenomanian rather than the Turonian, although this may be biased by the age of known fossiliferous deposits.
Highlights
Acanthomorpha was the term coined by Rosen (1973) to group the Paracanthopterygii and Acanthopterygii together with two fossil genera Ctenothrissa Woodward 1899 and Aulolepis Agassiz 1844, forming the largest group of teleost fishes
Davesne et al (2014) focused on the lampridiforms and their potential fossil members. Their analysis of osteological data from both extant and extinct taxa resulted in Polymixia being the sister group to the Paracanthopterygii plus Acanthopterygii, with the Lampridiformes being the sister group to this group (= Euacanthomorpha, comprising Paracanthopterygii + Acanthopterygii + Polymixia)
Chen et al (2014) used mitochondrial and nuclear gene markers in their analysis which resulted in Polymixia placed as the sistergroup to the Paracanthopterygii, with the Paracanthopterygii plus Polymixia together forming the sistergroup to the Acanthopterygii
Summary
Acanthomorpha was the term coined by Rosen (1973) to group the Paracanthopterygii and Acanthopterygii together with two fossil genera Ctenothrissa Woodward 1899 and Aulolepis Agassiz 1844, forming the largest group of teleost fishes. Davesne et al (2014) focused on the lampridiforms and their potential fossil members The number of fossil acanthomorphs known has recently increased significantly with new species described from throughout the Western Interior Seaway and Tethys Sea in the last decade These include, among others, Muhichthys cordobai, Pseudomonocentris microspinosus, Handuichthys interopercularis, Pepemkay maya and Zoqueichthys carolinae from Mexico (González-Rodríguez and Fielitz 2008; Alvarado-Ortega and Than-Marchese 2012, 2013; González-Rodríguez et al 2013), Aspesaipichthys cavaensis from Italy (Taverne, 2004), Errachidia pentaspinosa, Homalopagus multispinosus, Magrebichthys nelsoni and an unnamed form from Morocco (Murray and Wilson 2014), as well as two previously reported from the Lac des Bois locality, Boreiohydrias dayi and an unnamed form (Murray and Cumbaa, 2013). The new acanthomorph described here is from the northernmost known locality, Lac des Bois, situated just north of the Arctic Circle in the Northwest Territories, Canada
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