Essay on Reptiles
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Essay on Reptiles
Reptiles are vertebrate, or backboned animals constituting the class
Reptilia and are characterized by a combination of features, none of which
alone could separate all reptiles from all other animals...
Both snakes and
lizards are classified in this order, but lizards are separated into their
own suborder, Sauria...
In no special order, the
characteristics of reptiles are: cold-bloodedness; the presence of lungs;
direct development, without larval forms as in amphibians; a dry skin with
scales but not feathers or hair; an amniote egg; internal fertilization; a
three or four-chambered heart; two aortic arches (blood vessels) carrying
blood from the heart to the body, unlike mammals and birds that only have
one; a metanephric kidney; twelve pairs of cranial nerves; and skeletal
features such as limbs with usually five clawed fingers or toes, at least
two spinal bones associated with the pelvis, a single ball-and-socket
connection at the head-neck joint instead of two, as in advanced amphibians
and mammals, and an incomplete or complete partition along the roof of the
mouth, separating the food and air passageways so that breathing can
continue while food is being chewed...
A natural classification of reptiles is more difficult than that of many
animals because the main evolution of the group was during Mesozoic time (a
time of transition in the history of life and in the evolution of the
Earth); 13 of 17 recognized orders are extinct...
Proposals have been made to reclassify the
pterosaurs, dinosaurs, and certain other groups out of the class Reptilia
into one or more classes of their own...
Snakes and lizards, order
Squamata, are today the most numerous reptile species...
Lizards can be distinguished from snakes by the
presence of two pairs of legs, external ear openings, and movable eyelids,
but these convenient external diagnostic features, while absent in snakes,
are also absent in some lizards...
Thus, most of the questions of reptilian evolution and
classification deal with the reptiles’ interrelationship, rather than with
their relationships with other animals...
A third order of the class Reptilia is Crocodilia
...
Structurally, the tuatara is not much different from
related forms, also assigned to the order Rhynchocephalia, that may have
appeared as early as the Lower Triassic Period (over 2 000 000 000 years
ago
