''Mesacanthus'' ('middle spine') is an extinct genus of acanthodian
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...
from early
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...
.
[ It is among the more primitive of the Devonian acanthodians.
]
Description
''Mesacanthus'' body fossils have pectoral, pelvic, anal and dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
spines, as well as a pair of prepelvic spines, which are intermediate between the pectoral and pelvic fin spines.[ They also have small, unornamented, diamond shaped scales. According to Agassiz, the genus also has a distinct tail in which the upper lobe extends to a sharp point and the lower lobe forms a small triangle.][ Overall the genus is small (average length = 30mm) and fairly conservative, anatomically speaking, for acanthodians.][Agassiz, L. (1833). Recherches sur les poissons fossiles.. (Vol. 1). chez l'auteur.]
Taxonomy
The genus was erected by Ramsay Traquair
Ramsay Heatley Traquair FRSE FRS (30 July 1840 – 22 November 1912) was a Scottish naturalist and palaeontologist who became a leading expert on fossil fish.
Traquair trained as a medical doctor, but his thesis was on aspects of fish anatomy ...
in 1888 to accommodate certain species that had been previously assigned to Acanthodes
''Acanthodes'' (from el, ἄκανθώδης , 'provided with spines') is an extinct genus of spiny shark. Fossils have been found in Europe, North America, Asia, and Australia. ''Acanthodes'' was most common in the Carboniferous and Early Pe ...
by Louis Agassiz
Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history.
Spending his early life in Switzerland, he rec ...
.[Traquair, R. H. (1888). Old Red Sandstone fishes.] These species included ''Mesacanthus mitchelli'', ''Mesacanthus pusillus'', ''Mesacanthus peachi'' and ''Mesacanthus coriaceus''. [ The genus is found in both Lower Old Red Sandstone and Middle Old Red Sandstone assemblages, with ''M. pusillus'', ''M. peachi'' and ''M. coriaceus'' known from the Middle ]Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...
and ''M. mitchelli'' being the only known species from the Lower Devonian.[ ][ ]Arthur Smith Woodward
Sir Arthur Smith Woodward, FRS (23 May 1864 – 2 September 1944) was an English palaeontologist, known as a world expert in fossil fish. He also described the Piltdown Man fossils, which were later determined to be fraudulent. He is not rela ...
formally synonymized ''M. peachi'' and ''M. coriaceus'' in 1891.[Woodward, A. S. (1901). Catalogue of the fossil fishes in the British Museum (Natural History). Printed by order of the Trustees.] In 2015 a study published in PeerJ
''PeerJ'' is an open access peer-reviewed scientific mega journal covering research in the biological and medical sciences. It is published by a company of the same name that was co-founded by CEO Jason Hoyt (formerly at Mendeley) and publisher Pe ...
reassessed the two remaining Middle Devonian species (''M. pusillus'' and ''M. peachi'') and found that they also could not be distinguished from one another. Hence, only two species from the Orcadian Basin and Midland Valley areas of Scotland are currently considered to be valid: ''M. mitchelli'' from the Lower Devonian and ''M. pusillus'' from the Middle Devonian.[
]
See also
* List of acanthodians
This list of acanthodian genera is an attempt to create a comprehensive listing of all genera that have ever been included in the subclass Acanthodii, excluding purely vernacular terms. The list includes all commonly accepted genera, but also gen ...
References
{{Taxonbar, from=Q6821111
Acanthodii genera
Devonian acanthodians
Prehistoric life of Europe