Two late Scottish relatives of Jamoytius

Cornovichthys blaauweni.

The now flooded Achanarras fish beds in Caithness, Northern Scotland, has yielded an abundant collection of fossil fish belonging to some 15 genera dating from the Eifelian stage (about 390 MYA) of the Middle Devonian period. These include the arthrodire (a group of heavily armored jawed fish) Coccosteus cuspidatus, the Acanthodians (“spiny sharks”) Diplacanthus, Mesacanthus and Cheiracanthus, the enigmatic Palaeospondylus gunni, the early Actinopterygian (ray-finned fish) Cheirolepis treilli and the Sarcopterygians (lobed-finned fish) Osteolepis macrolepidotus and Dipterus valenciennesi. The agnathans (jawless fish) are a rarity there and consist of only two species, Cornovichthys blaaweni and Achanarella trewini, which are believed to be closely related to Jamoytius kerwoodi from the Silurian, and placed in the clade Jamoytiiforms. The limestone of Achanarras quarry has been deposited in what appear to have been a deep freshwater lake environment.

Cornovichthys blaauweni is known from a single carbonaceous impression of a complete specimen measuring a little over 10 cm in length. The body is long and slender with a hypocercal tail and a quite large anal fin. There is no evidence of any other fin, nor of any scale in the specimen. Eyes appear to be situated near the top surface of the head. Overall, Cornovichthys looks a lot like Euphanerops and like its Canadian counterpart has a long series of branchial openings running from the head to the anal fin, numbering to around 15 on each side of the body.

Achanarella trewini.

Achanarella trewini is known from many specimens that were found in large numbers on single slabs of rock. Individuals of Achanarella range in size from 2 cm to 9 cm in length. Like Cornovichthys, it has a hypocercal tail and a large anal fin, no apparent scale and a large number of branchial openings on each side of the body, 13 or more, but the body is much thinner and elongated and the head is extremely small. Just like Jamoytius and Euphanerops, Cornovichthys and Achanarella were probably feeding on micro-organisms and detritus through their jawless mouth.

Reference:

Newman, M., & Trewin, N. (2001). A new jawless vertebrate from the Middle Devonian of Scotland. Palaeontology, 44, 43–51.

Newman, M. (2002). A new naked jawless vertebrate from the Middle Devonian of Scotland. Palaeontology, 45(5), 933–941.

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 Stensiö 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.