Authors: Cook, Todd D.; Wilson, Mark V.H.; Murray, Alison M.

Source: Canadian Journal of Earth Sciences, Volume 45, Number 10, October 2008 , pp. 1185-1197(13)

Publisher: NRC Research Press

Abstract:

A euselachian assemblage was recovered from the middle Cenomanian Dunvegan Formation situated in northwestern Alberta. This assemblage is the most northern described within the Western Interior Seaway and provides an important insight into the euselachian faunal diversity of this little-known region of the seaway. Despite its high paleolatitude, the assemblage contains a number of elasmobranch taxa, including Hybodus, Squalicorax, Archaeolamna, Cretodus, Dallasiella, and Cretoxyrhina. The Dunvegan assemblage also contains the first known reports from Canada of the odontaspid shark Johnlongia parvidens, the cretoxyrhinid shark Protolamna carteri, and the ray Pseudohypolophus mcnultyi. This assemblage extends the northern geographical range of all taxa. Preliminary comparisons with other middle Cenomanian Western Interior Seaway assemblages show that the core composition of the Dunvegan assemblage is remarkably similar to that of other time-equivalent assemblages; however, conspicuously absent are species that are exceedingly common in other localities situated farther south. We suggest that absence of these taxa from the Dunvegan localities may be caused by a temperature intolerance associated with latitude and sea-water circulation patterns, or by an inability to inhabit environments that exhibit salinity variation.

Un assemblage euselachien a été récupéré dans la Formation de Dunvegan du Cénomanien moyen du nord-ouest de l'Alberta. Cet assemblage est le plus septentrionaux décrits à ce jour provenant des dépôts de la mer intérieure de l'Ouest et il jette un important éclairage sur la diversité faunique euselachienne dans cette région méconnue du bassin. Malgré sa haute paléolatitude, l'assemblage contient divers taxons d'élasmobranches, dont Hybodus, Squalicorax, Archaeolamna, Cretodus, Dallasiella et Cretoxyrhina. L'assemblage de Dunvegan contient également les premiers spécimens signalés au Canada du requin odontaspide Johnlongia parvidens, du requin crétoxyrhinide Protolamna carteri et de la raie Pseudohypolophus mcnultyi. L'assemblage repousse les limites septentrionales de la distribution géographique de tous ces taxons. Des comparaisons provisoires avec d'autres assemblages du Cénomanien moyen de la mer intérieure de l'Ouest démontrent que la composition de base de l'assemblage de Dunvegan et celles d'autres assemblages contemporains présentent une remarquable similitude; certaines espèces par ailleurs très répandues en d'autres lieux plus méridionaux brillent toutefois par leur absence. Il est postulé que l'absence de ces taxons dans l'assemblage de Dunvegan pourrait être le résultat d'une intolérance à la température associée à la latitude et aux courants marins, ou encore de l'incapacité de ces taxons à s'implanter dans des milieux présentant des variations de salinité.

Document Type: Research article

Publication date: 2008-10-01

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