Kids Research Express

. Reptile, animal with tough, dry skin covered with horny scales. Some of the most widespread living reptiles are turtles , lizards , snakes , crocodiles , and alligators . Reptiles are vertebrates —animals that have a backbone. While they share characteristics common to other vertebrates—fish, amphibians, birds, and mammals—reptiles display a unique combination of characteristics that distinguishes them from other vertebrates. Like amphibians, modern reptiles are cold-blooded, or ectothermic. This means that they are unable to produce their own body heat, so they rely on the sun for warmth, and much of their behavior is directed toward regulating their body temperature. Like birds, most reptiles hatch from eggs that are laid on land, covered by a protective shell. Reptiles breathe air with lungs, as do most mature amphibians and all birds and mammals. And like amphibians and mammals, most reptiles, with the exception of turtles, have teeth. Reptile skin, with its tough, horny scales,

. There are over 40,000 species of vertebrates, which scientists classify into five groups: (1) fish , (2) amphibians , (3) reptiles , (4) birds , and (5) mammals . Scientists divide fish into three groups based on their anatomy: jawless fish, cartilaginous fish, and bony fish. The other vertebrate groups are made up of tetrapods, which have lungs and generally live on land. Jawless fishes -> Cold-blooded animals that live in water. These fishes have no bone structure and their sole support is from a simple cartilaginous rod known as the notochord. Unlike other vertebrates, these fishes do not have opposing jaws. They have round, sucker-like mouths and use tongues with embedded teeth that scrape tissue from prey. Jawless fishes have primitive breathing openings that provide oxygen to the blood. They reproduce by laying eggs. - Examples: Hagfish, lamprey Cartilaginous fishes -> Cold-blooded animals that live in water. Their notochord is surrounded by rings of cartilage known as