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''Birkenia'' is a genus of extinct
/ref> Birkeniid anaspids are covered by a series of small plates on the head and rod-shaped scales in a cheveron-like pattern on the trunk.
Intact fossil specimens of ''B. elegans'' suggest the living animal reached a length of up to , and was an active swimmer. In addition to whole specimens and scale microfossils of ''B. elegans'', which are found in Great Britain and Scandinavia, scales of a second species, ''B. robusta,'' are found in Late Silurian strata of Scandinavia and Estonia. The scales of ''B. robusta'' differ from those of ''B. elegans'' in that, as the specific epithet suggests, the scales of the former are more robustly proportioned than those of the latter. Fossil specimens also show a rib that is modified by being narrow at the ends and gradually broadens and rises towards the middle of the scale, where a major elevation is developed that is expressed as a raised and slightly angled ridge.
anaspid
Anaspida ("shieldless ones") is an extinct group of jawless fish that existed from the early Silurian period to the late Devonian period. They were classically regarded as the ancestors of lampreys, but it is denied in recent phylogenetic analy ...
fish from Middle Silurian
The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
strata of Northern Europe, and Middle Silurian to possibly Earliest Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
strata of Arctic Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
.Blom, Henning, T. Märss, and C. G. Miller. "Silurian and earliest Devonian birkeniid anaspids from the Northern Hemisphere." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 92.03 (2001): 263-323/ref> Birkeniid anaspids are covered by a series of small plates on the head and rod-shaped scales in a cheveron-like pattern on the trunk.
Intact fossil specimens of ''B. elegans'' suggest the living animal reached a length of up to , and was an active swimmer. In addition to whole specimens and scale microfossils of ''B. elegans'', which are found in Great Britain and Scandinavia, scales of a second species, ''B. robusta,'' are found in Late Silurian strata of Scandinavia and Estonia. The scales of ''B. robusta'' differ from those of ''B. elegans'' in that, as the specific epithet suggests, the scales of the former are more robustly proportioned than those of the latter. Fossil specimens also show a rib that is modified by being narrow at the ends and gradually broadens and rises towards the middle of the scale, where a major elevation is developed that is expressed as a raised and slightly angled ridge.
References
Birkeniiformes Silurian fish of North America Silurian fish of Europe Llandovery genus first appearances Early Devonian genus extinctions Early Devonian fish of North America Fossil taxa described in 1899 Birkeniiformes genera {{Paleo-jawless-fish-stub