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Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes).They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras.
Ischnacanthiformes is a prehistoric order of "acanthodian" stem-chondrichthyans found in Canada, Ukraine and United Kingdom. Members of this order were nektonic carnivores, [1] eating animals that swim rather than plankton. They had slender builds, light armor, deeply inserted spines, shark-like teeth, and two dorsal fins. [1]
Various primitive acanthodians from Early Devonian England and Scotland, Mesacanthus pusillus, Parexus falcatus, Ishnacanthus gracilis.. 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.
Cheiracanthus (from Greek: χείρ kheír, 'hand' and Greek: ἄκανθα akantha, 'spine') [1] is an extinct genus of a group of fish called Acanthodii (or "spiny sharks"). [2] It was a deep-bodied acanthodian about 12 in. (30 cm) in length. It had a blunt head, upturned tail, and fins protected by spines.
The common name "spiny sharks" is really a misnomer for these early jawed fishes. The name was coined because they were superficially shark-shaped, with a streamlined body, paired fins, and a strongly upturned tail; stout bony spines supported all the fins except the tail – hence, "spiny sharks".
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Parexus is an extinct genus of acanthodian fish. Acanthodians are often referred to as ‘spiny sharks’, although acanthodians are not true sharks and evolved perhaps 50 million years earlier than sharks. Acanthodians share several features with bony fish and cartilaginous fish; they often have spines supporting their fins.
The new species doesn’t have lateral lacrimal or second preopercular spines, meaning a spine on the head and the front of the gills. The fish also has much longer lower pectoral-fin rays, the ...