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Falcate means sickle-shaped or hook-shaped. Some whales, like orcas, have a falcate-shaped dorsal fin.
Filter feeders are animals that eat by sieving through lots of sea water and straining out tiny bits of nourishment. The Whale shark, Basking shark, and Megamouth shark are filter feeders, obtaining plankton by sieving water through their gill slits.
The finetooth shark (Carcharhinus isodon) is a shark that lives in shallow inshore waters off the eastern coast of the Americas in the Atlantic ocean. It has dark gray skin above, lighter skin below; there is a slight white band along the flank. Males are about 5.2 feet (1.6 m) long, females are about 4.9 feet (1.5 m) long. It has a pointed snout and long gill slits. The teeth are very small, fine, and clear. This shark often congregates in large schools. It eats small fishes and cephalopods. They are viviparous; there are 1 to 6 pups in each litter. At birth, pups are from 1.5 and 2 ft long Very little is known about this shark. Clasification: order Carcharhiniformes, family Carcharhinidae genus Carcharhinus, species C. isodon. The species name, isodon, means equal tooth; it was named isodon because this shark has the same number of teeth in the upper and lower jaws.
Sharks have existed for over 350 million years. They evolved over 100 million years before the dinosaurs did. This was long before people evolved. Most fossil evidence of early sharks is from fossilized teeth and a few skin impressions. Cladodonts, primitive sharks, had double-pointed teeth, were up to 3 feet (1 m) long fish-eaters and lived about 400 million years ago (mya). The earliest-known primtitive shark remains are fossil "scales" that date from about 420 million years ago, during the early Silurian. The earliest shark genera are Mongolepis, Polymerolepis, and Palaeospondylus.
Chlamydoselachus anguineus, also known as the eel shark, is a long, thin shark with a very long tail fin and a short snout. It grows to be up to 6.5 feet (2 m) long and is a light-brown color. It has 6 pairs of long gill slits (6 slits on each side of the body behind the head). Each gill slit is covered by frills of skin, hence its name. Its teeth have 3 cusps on a wide base. It has an anal fin and one small dorsal fin. The pectoral fins are short and rounded. The frilled shark is viviparous, giving birth to 8 to 12 live young in a litter after a gestation period of about 1 to 2 years. Pups are about 16 inches (40 cm) long. This shark is harmless to people and is found in the eastern Atlantic Ocean, the eastern Pacific Ocean, and the western Indian Ocean. It generally lives deep in the ocean (about 330-4,260 feet or 100-1,300 m deep) but is occasionally found at the surface. Very little is known about this shark. (Order Hexanchiformes, Family Chlamydoselachidae)
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