Search results
Results from the WOW.Com Content Network
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.
Xenacanthida (or Xenacanthiformes) is an order or superorder of extinct shark-like chondrichthyans (cartilaginous fish) known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. [1] Some xenacanths may have grown to lengths of 5 m (16 ft). [2]
Stethacanthidae is an extinct family of prehistoric sharks. [1] It is estimated to have existed approximately between 380 and 300 million years ago. Members of this family are noted for their peculiar dorsal fin.
Helicoprion is a genus of extinct shark-like [1] eugeneodont fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most extinct cartilaginous fish, the skeleton is mostly unknown.
Spiny sharks (extinct) were the earliest known jawed fish. They resembled sharks and were ancestral to them. Spiny sharks, class Acanthodii, are extinct fish that share features with both bony and cartilaginous fish, though ultimately more closely related to and ancestral to the latter. Despite being called "spiny sharks", acanthodians predate ...
Sharks could be facing extinction over the next couple of decades. Human interference is largely to blame for the species interference. Overfishing of sharks has increased as the global demand has ...
In the late 1920s, Dr. Erik Stensiö, at the Swedish Museum of Natural History in Stockholm, established the details of placoderm anatomy and identified them as true jawed fishes related to sharks. He took fossil specimens with well-preserved skulls and ground them away, one tenth of a millimeter at a time.
Symmoriiformes were previously regarded as members of the elasmobranchii, making them distant relatives of living sharks and rays.Zangerl (1981), who erected the order, considered them to be elasmobranchs, [1] and this classification has been followed by some subsequent authors.