Sunday, May 4, 2014

The Canadian cousins of Jamoytius

Euphanerops longaevus

The rich Late Devonian fish fauna of Miguasha, in Eastern Quebec, Canada (Escuminac Formation) includes some peculiar jawless fish closely related to the Silurian scottish species Jamoytius kerwoodi. They have a strongly hypocercal tail with a relatively large anal fin. The body is elongated and have a series of long and narrow weakly mineralized scales on the flanks. The eyes are relatively large and the mouth is a circular opening situated at the bottom of the head. Like most if not all primitive fish, they lack paired fins. The branchial openings were numerous numbering 30 or so (lampreys have only 7 of these gill pouches) aligned from the head to the anal region, and therefore stretching over a very long portion of the body. This peculiar arrangement is thought to be an adaptation to a poorly oxygenated water. The first species to be described is Euphanerops longaevus by the British paleontologist Sir Arthur Smith Woodward in 1900. This strange animal was however originally described upside down, with the anal fin as a dorsal one and an epicercal tail. Euphanerops measured about 10 cm in length. The second species is Endeiolepis aneri described by the swedish paleontologist Erik Stensiƶ in 1939. It is very similar to Euphanerops and it was suggested that the two represent the same animal, with Euphanerops being the juvenile form. In that case, the name Euphanerops has priority and Endeiolepis would be a junior synonym. Legendrelepis parenti described by M. Arsenault and P. Janvier, 1991 is considered to be a junior synonym as well, any noted differences such as the alleged presence of a dorsal fin are now viewed as artifacts of preservation.

References:

Janvier, P., Desbiens, S., Willett, J. a, & Arsenault, M. (2006). Lamprey-like gills in a gnathostome-related Devonian jawless vertebrate. Nature, 440(7088), 1183–5. 

Janvier, P., & Arsenault, M. (2007). The anatomy of Euphanerops longaevus Woodward, 1900, an anaspid-like jawless vertebrate from the Upper Devonian of Miguasha, Quebec, Canada. Geodiversitas, 29(1), 143–216.

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