Birkeniidae

	Birkeniidae Birkeniidae is an extinct family of jawless fish belonging to the order Birkeniiformes 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 .... They were defined in 1899 by Ramsay H. Traquair, and were a successful family among the many jawless fish in the Silurian seas. Morphology Birkeniidae had a large body which was ovular in shape, and a strong, mobile tail. Their eyes were positioned on either side of the head. Their mouth was large for the jawless fish, but contained no teeth. Birkeniidae are distinguished by the crown shaped projection on their back, and the other smaller projections which run down its tail. They also possessed fins which faced downwards, an uncommon trait among the jawless fish. They had typical scaly skin. References External links * Birkeniifor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Birkeniiformes 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 analysis, although some analysis show these group would be at least related. Anaspids were small marine fish that lacked a heavy bony shield and paired fins, but were distinctively hypocercal. Anatomy Compared to many other ostracoderms, such as the Heterostraci and Osteostraci, anaspids did not possess a bony shield or armor, hence their name. The anaspid head and body are instead covered in an array of small, weakly mineralized scales, with a row of massive scutes running down the back, and, at least confirmed among the birkeniids, the body was covered in rows of tile-like scales made of aspidine, an acellular bony tissue. Anaspids all had prominent, laterally placed eyes with no sclerotic ring, with the gills opened as a row of holes along ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Ctenopleuron ''Ctenopleuron'' is an extinct genus of jawless fish in the class Anaspida 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 anal .... It is considered to have existed in the Paleozoic epoch between 423 and 419 Ma. References External links * Birkeniiformes genera Fossil taxa described in 1907 {{paleo-jawless-fish-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Birkenia ''Birkenia'' is a genus of extinct Anaspida, anaspid fish from Middle Silurian strata of Northern Europe, and Middle Silurian to possibly Earliest Devonian strata of Arctic Canada.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 e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Saarolepis ''Rhyncholepis'' was an extinct genus of anaspid from the Late Silurian. Fossils of species ''R. butriangula'' and ''R. parvula'' have been found in Ringerike, Norway, and Oesel, Estonia. The genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ... has two species, described in 1911 and 2002. Discovery ''Rhyncholepis parvula'' was discovered and originally described in 1911, and described in more detail in 1924 by Norwegian Professor Johan Kiær. In the associated monograph, Kiær describes the genus in great detail, along with several other anaspids discovered around the same time. More recently, the second discovered species (''R. butriangula'') was described by Henning Blom, Tiiu Märss, and C. Giles Miller in 2002. References Birkeniiformes Silurian jawless fish ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]