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Zenaspida
Zenaspidida is an extinct order of osteostracans, a group of jawless stem- gnathostomes. They possessed a distinct headshield, which varied in width to length ratio by species. Description The head shield is dome-shaped and extremely large in comparison to the main body. The abdominal section of this shield has a less developed median dorsal crest. As a rule for this order, the nasohypophysial opening is larger than the nasal division. The pineal plate seen in other osteostracans is barely developed or completely absent. The median dorsal field is notably broad, and the lateral fields are widened in the posterior, but reach back no further than the proximal section of the dorsal surface of the cornual processes. The ornamentation on the head shield can have singular, large tubercles, or groups of tubercles which range in size. This is often used to speciate. Classification The cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "characte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Osteostracan
The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian. Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans. This is due to the development of paired fins, and their complicated cranial anatomy. The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear, as opposed to the three pairs found in the inner ears of jawed vertebrates. They are thought to be the sister-group to pituriaspids, and together, these two taxa of jawless vertebrates are the sister-group of gnathostomes. Several synapomorphies support this hypothesis, such as the presence of: sclerotic ossicles, paired pectoral fins, a dermal skeleton with three layers (a basal layer of isopedin, a middle layer o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Osteostraci
The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish, termed " ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian. Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans. This is due to the development of paired fins, and their complicated cranial anatomy. The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear, as opposed to the three pairs found in the inner ears of jawed vertebrates. They are thought to be the sister-group to pituriaspids, and together, these two taxa of jawless vertebrates are the sister-group of gnathostomes. Several synapomorphies support this hypothesis, such as the presence of: sclerotic ossicles, paired pectoral fins, a dermal skeleton with three layers (a basal layer of isopedin, a middle layer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zenaspis
''Zenaspis'' is an extinct genus of osteostracan jawless fish which existed during the early Devonian period. Due to it being jawless, ''Zenaspis'' was probably a bottom feeder. ''Zenaspis'' was around 10 inches (25 cm) in length. It had a horseshoe shaped head that probably sheltered a small brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for .... Osteostraci genera Devonian jawless fish Early Devonian fish of Europe {{Devonian-jawless-fish-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superciliaspis
''Superciliaspis'' is an extinct genus of jawless fish which existed in what is now the Northwest Territories of Canada during the Lochkovian age. Originally identified as a species of ''Cephalaspis ''Cephalaspis'' (from , 'head' and , 'shield') is a possibly monotypic genus of extinct osteostracan agnathan vertebrate. It was a trout-sized detritivorous fish that lived in the early Devonian. Description Like its relatives, ''Cephalaspi ...'' (''C. gabrielsi'') by Dineley and Loeffler in 1976, it was reassigned to ''Superciliaspis gabrielsi'' by Adrain and Wilson in 1994. References Osteostraci genera Fossils of British Columbia Enigmatic fish taxa Devonian jawless fish Fossil taxa described in 1994 {{Devonian-jawless-fish-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
