Reptiles, the reptilian class, are an evolutionary grade of animals. The reptile family is an order and class of a large family of species that all evolved from each other. These 3 groups being Crocodilian, Squamata and Testudines. Reptiles have been around for millions of years. The first known reptiles appeared 340 to 335 million years ago during the Carboniferous period, having evolved from advanced reptile-like amphibians that increasingly adapted to life on dry land. Although some reptiles live on land, water, or land and water, reptiles come in many different shapes, sizes, and colors. There are many groups of reptiles that have become extinct due to mass extinction events. Reptiles are tetrapod vertebrates, meaning they have four limbs, or snake-like descended from limbed ancestors. Most reptiles are oviparous, meaning they lay eggs, although some reptiles are viviparous, meaning they carry a fetus in their stomach. The crocodilian has 25 species, the squamata have more than 9,600, and the testudines have about 400. The crocodilian is an order of large, predatory semi-aquatic reptiles that have existed for millions of years. About 83.5 million years ago, when the crocodilian first appeared, the crocodilian family includes alligators, caimans, and the gavial family. Crocodilians are a massive, solid lizard-like reptile that has a long, flattened snout and a compressed tail. Crocodilians are elite swimmers and can also move on land in a "high or low walk", some smaller species can even gallop. These reptiles have a four-chambered heart that somewhat resembles that of birds and have a system of unidirectional loops o...... middle of paper ...... fascinating groups about the world's species. Some of these species can live for decades, whether they are turtle lizards or snakes, and these animals date back to the Jurassic Park era. Reptiles come in all shapes and sizes, some have scales and some have shells, but they are all cold-blooded animals. All reptiles fall into an order, some are higher in the order than others. The classification of reptiles is difficult to distinguish unlike other animals because the main period of evolution is during the Mesozoic period. Scientists are still studying these amazing creatures and learning more and more about the era from which they originated. It's amazing to think that some of the ancestors of these creatures were roaming around with the dinosaurs at one point. The reptile family consists of an order and a class of a large family of species that all evolved from each other.