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Dorsal fin diagram with landmarks labeled. Fins allow the sharks to be able to guide and lift themselves. Most sharks have eight fins: a pair of pectoral fins, a pair of pelvic fins, two dorsal fins, an anal fin, and a caudal fin. Pectoral fins are stiff, which enables downward movement, lift, and guidance.
A shark, also called a "selachimorph", can be described as all of the following: Animal – multicellular, eukaryotic organism of the kingdom Animalia or Metazoa. An animal's body plan eventually becomes fixed as it develops, although some types of animal undergo a process of metamorphosis later on in their life.
Any fossils, including fossil shark teeth, are preserved in sedimentary rocks after falling from their mouth. [13] The sediment that the teeth were found in is used to help determine the age of the shark tooth due to the fossilization process. [15] Shark teeth are most commonly found between the Upper Cretaceous and Tertiary periods. [16]
The top jaw has jagged, cusped teeth and the bottom jaw has comb-shaped teeth. Its single dorsal fin is set far back along the spine towards the caudal fin, and is behind the pelvic fins. In this shark the upper caudal fin is much longer than the lower, and is slightly notched near the tip. Like many sharks, this sevengill is counter-shaded.
Sawfish are not sharks, but a type of ray. The gill slits of the sawfishes are positioned on the underside like a ray, but the gill slits of the saw shark are positioned on the side like a shark. Sawfish can have a much larger size, lack barbels, and have evenly sized teeth rather than alternating teeth of the saw shark.
The kitefin shark, the largest luminous vertebrate on record, [3] has a slender body with a very short, blunt snout, large eyes, and thick lips. Its teeth are highly differentiated between the upper and lower jaws, with the upper teeth small and narrow and the lower teeth large, triangular, and serrated.
Researchers found fossilized teeth belonging to “the immediate ancestor of the giant megalodon shark,” Moore said. “This shark evolved into the megalodon, which was the largest of all sharks ...
The bluntnose sixgill is a species of sixgill sharks, of genus Hexanchus, a genus that also consists of two other species: the bigeye sixgill shark (Hexanchus nakamurai) and the Atlantic sixgill shark (Hexanchus vitulus). Through their base pairs of mitochondrial genes COI and ND2, these three species of sixgills widely differ from one another.