Zoo, also called zoological garden or zoological park, place where wild animals and, in some instances, domesticated animals are exhibited in captivity.. Most long-established zoos exhibit general collections of animals, but some formed more recently specialize in particular groups�e.g., primates, big cats, tropical birds, or waterfowl. Marine invertebrates, fishes, and marine mammals often are kept in separate establishments known as aquariums.
Traditionally, reptiles are members of the class Reptilia comprising the amniotes that are neither birds nor mammals. (The amniotes are the vertebrates with eggs featuring an amnion, a double membrane that permits the embryo to breathe effectively on land.) Living reptiles, in that sense, can be distinguished from other tetrapods in that they are cold-blooded and bear scutes or scales.
Reptiles originated around 320-310 million years ago during the Carboniferous period, having evolved from advanced reptile-like amphibians that became increasingly adapted to life on dry land. There are many extinct groups, including dinosaurs, pterosaurs, and aquatic groups such as the ichthyosaurs. Modern reptiles inhabit every continent with the exception of Antarctica. Several living sub-groups are recognized:
� Testudines (turtles, terrapins and tortoises): approximately 330 species.
� Sphenodontia (tuataras from New Zealand): 2 species
� Squamata (lizards, snakes, and worm lizards): over 9,000 species.
� Crocodilia (crocodiles, gavials, caimans, and alligators): 25 species[
Although they have scutes on their feet and lay eggs, birds have historically been excluded from the reptiles, in part because they are warm-blooded. They therefore do not appear on the list above. However, as some reptiles are more closely related to birds than they are to other reptiles � crocodiles are more closely related to birds than they are to lizards � cladistic writers who prefer a more unified (monophyletic) grouping usually also include the birds, which include over 10,000 species.
January 20th, 2013
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