   #copyright

Reptile

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

   iReptiles

                    Fossil range: Carboniferous - Recent

   Eastern Hermann's Tortoise
   Eastern Hermann's Tortoise
                Scientific classification

   Kingdom:   Animalia
   Phylum:    Chordata
   Subphylum: Vertebrata
   Class:     Sauropsida
              Goodrich, 1916

                                   Orders

     * Procolophonia (extinct)
     * Testudines
     * Araeoscelidia (extinct)
     * Avicephala (extinct)
     * Younginiformes (extinct)
     * Sauropterygia
          + Ichthyosauria (extinct)
          + Placodontia (extinct)
          + Nothosauria (extinct)
          + Plesiosauria (extinct)
     * Sphenodontia
     * Squamata
     * Prolacertiformes (extinct)
     * Archosauria
          + Crurotarsi
               o Order Aetosauria
               o Order Phytosauria
               o Order Rauisuchia
               o Order Crocodilia
          + Ornithodira
               o Pterosauria (extinct)
               o Marasuchus (extinct)
               o Dinosauria (extinct)
                    # Order Saurischia
                    # Order Ornithischia

   Reptiles are tetrapods and amniotes, animals whose embryos are
   surrounded by an amniotic membrane. Today they are represented by four
   surviving orders:
     * Crocodilia (crocodiles, caimans and alligators): 23 species
     * Sphenodontia (tuataras from New Zealand): 2 species
     * Squamata ( lizards, snakes and amphisbaenids ("worm-lizards")):
       approximately 7,600 species
     * Testudines (turtles): approximately 300 species

   Reptiles are found on every continent except for Antarctica, although
   their main distribution comprises the tropics and subtropics. Though
   all cellular metabolism produces some heat, most modern species of
   reptiles do not generate enough to maintain a constant body temperature
   and are thus referred to as " cold-blooded" or ectothermic (the
   Leatherback Sea Turtle is an exception). Instead, they rely on
   gathering and losing heat from the environment to regulate their
   internal temperature, e.g, by moving between sun and shade, or by
   preferential circulation — moving warmed blood into the body core,
   while pushing cool blood to the periphery. In their natural habitats,
   most species are adept at this, and can ususally maintain core body
   temperatures within a fairly narrow range, comparable to that of
   mammals and birds, the two surviving groups of " warm-blooded" animals.
   While this lack of adequate internal heating imposes costs relative to
   temperature regulation through behaviour, it also provides a large
   benefit by allowing reptiles to survive on much less food than
   comparably-sized mammals and birds, who burn much of their food for
   warmth. While warm-blooded animals move faster in general, an attacking
   lizard, snake or crocodile moves very quickly.

   Except for a few members of the Testudines, all reptiles are covered by
   scales.

   Most reptile species are oviparous (egg-laying). Many species of
   squamates, however, are capable of giving live birth. This is achieved,
   either through ovoviviparity (egg retention), or viviparity (babies
   born without use of calcified eggs). Many of the viviparous species
   feed their fetuses through various forms of placenta analogous to those
   of mammals (Pianka & Vitt, 2003 pgs: 116-118). They often provide
   considerable initial care for their hatchlings.

Classification of reptiles

   Reptiles are a paraphyletic group. The group can be made monophyletic
   by including the birds (Aves).
   Enlarge
   Reptiles are a paraphyletic group. The group can be made monophyletic
   by including the birds (Aves).

   From the classical standpoint, reptiles included all the amniotes
   except birds and mammals. Thus reptiles were defined as the set of
   animals that includes crocodiles, alligators, tuatara, lizards, snakes,
   amphisbaenians and turtles, grouped together as the class Reptilia
   (Latin repere, "to creep"). This is still the usual definition of the
   term.

   However, in recent years, many taxonomists have begun to insist that
   taxa should be monophyletic, that is, groups should include all
   descendants of a particular form. The reptiles as defined above would
   be paraphyletic, since they exclude both birds and mammals, although
   these also developed from the original reptile. Colin Tudge writes:

          Mammals are a clade, and therefore the cladists are happy to
          acknowledge the traditional taxon Mammalia; and birds, too, are
          a clade, universally ascribed to the formal taxon Aves. Mammalia
          and Aves are, in fact, subclades within the grand clade of the
          Amniota. But the traditional class reptilia is not a clade. It
          is just a section of the clade Amniota: the section that is left
          after the Mammalia and Aves have been hived off. It cannot be
          defined by synamorphies, as is the proper way. It is instead
          defined by a combination of the features it has and the features
          it lacks: reptiles are the amniotes that lack fur or feathers.
          At best, the cladists suggest, we could say that the traditional
          Reptila are 'non-avian, non-mammalian amniotes'. (Tudge, p.85)

          By the same token, the traditional class Amphibia becomes
          Amphibia*, because some ancient amphibian or other gave rise to
          all the amniotes; and the phylum Crustacea becomes Crustacea*,
          because it may have given rise to the insects and myriapods
          (centipedes and millipedes). If we believe, as some (but not
          all) zoologists do, that myriapods gave rise to insects, then
          they should be called Myriapoda*....by this convention Reptilia
          without an asterisk is synonymous with Amniota, and includes
          birds and mammals, whereas Reptilia* means non-avian,
          non-mammalian amniotes. (Tudge, p.85)

   Recent college-level references, such as Benton (2004) , offer another
   compromise by applying traditional ranks to accepted phylogenetic
   relationships. In this case, reptiles belong to the class Sauropsida,
   and mammal-like reptiles to the class Synapsida, with birds and mammals
   separated into their own traditional classes.

Reptile Groups

     * Class Sauropsida
          + Family Captorhinidae (extinct)
          + Family Protorothyrididae - Hylonomus (extinct)
          + Subclass Anapsida
               o Family Mesosauridae (extinct)
               o Order Procolophonia - incl. Pareiasaurs (extinct)
               o ?Order Testudines - Turtles
          + Subclass Diapsida
               o Superorder Ichthyopterygia - Ichthyosaurs (extinct)
               o Infraclass Lepidosauromorpha
                    # Superorder Sauropterygia - Plesiosaurs (extinct)
                    # Superorder Lepidosauria
                         @ Order Sphenodontia - Tuatara
                         @ Order Squamata - Lizards & Snakes
               o Infraclass Archosauromorpha
                    # Order Crocodilia - Crocodilians
                    # Order Pterosauria - Pterodactyls (extinct)
                    # Superorder Dinosauria - Dinosaurs
                         @ Class Aves - Birds

Evolution of the reptiles

   Young American Alligator Georgetown, South Carolina
   Enlarge
   Young American Alligator
   Georgetown, South Carolina

   Hylonomus is the oldest-known reptile, and was about 8 to 12 inches (20
   to 30 cm) long. Westlothiana has been suggested as the oldest reptile,
   but is for the moment considered to be more related to amphibians than
   amniotes. Petrolacosaurus and Mesosaurus are other examples. The first
   true "reptiles" (Sauropsids) are categorized as Anapsids, having a
   solid skull with holes only for nose, eyes, spinal cord, etc. Turtles
   are believed by some to be surviving Anapsids, as they also share this
   skull structure; but this point has become contentious lately, with
   some arguing that turtles reverted to this primitive state in order to
   improve their armor. Both sides have strong evidence, and the conflict
   has yet to be resolved.

   Shortly after the first reptiles, two branches split off, one leading
   to the Anapsids, which did not develop holes in their skulls. The other
   group, Diapsida, possessed a pair of holes in their skulls behind the
   eyes, along with a second pair located higher on the skull. The
   Diapsida split yet again into two lineages, the lepidosaurs (which
   contain modern snakes, lizards and tuataras, as well as, debatably, the
   extinct sea reptiles of the Mesozoic) and the archosaurs (today
   represented by only crocodilians and birds, but also containing
   pterosaurs and dinosaurs).

   The earliest, solid-skulled amniotes also gave rise to a separate line,
   the Synapsida. Synapsids developed a pair of holes in their skulls
   behind the eyes (similar to the diapsids), which were used to both
   lighten the skull and increase the space for jaw muscles. The synapsids
   eventually evolved into mammals, and are often referred to as
   mammal-like reptiles, though they are not true members of the class
   Sauropsida.

Systems

Circulatory

   Thermographic image of a monitor lizard.
   Enlarge
   Thermographic image of a monitor lizard.

   Most reptiles have closed circulation via a three-chamber heart
   consisting of two atria and one, variably-partitioned ventricle. There
   is usually one pair of aortic arches. In spite of this, due to the
   fluid dynamics of blood flow through the heart, there is little mixing
   of oxygenated and deoxygenated blood in the three-chamber heart.
   Furthermore, the blood flow can be altered to shunt either deoxygenated
   blood to the body or oxygenated blood to the lungs, which gives the
   animal greater control over its blood flow, allowing more effective
   thermoregulation and longer diving times for aquatic species. There are
   some interesting exceptions among reptiles. For instance, crocodilians
   have an incredibly complicated four-chamber heart that is capable of
   becoming a functionally three-chamber heart during dives (Mazzotti,
   1989 pg 47). Also, it has been discovered that some snake and lizard
   species (e.g., monitor lizards and pythons) have three-chamber hearts
   that become functional four-chamber hearts during contraction. This is
   made possible by a muscular ridge that subdivides the ventricle during
   ventricular diastole and completely divides it during ventricular
   systole. Because of this ridge, some of these squamates are capable of
   producing ventricular pressure differentials that are equivalent to
   those seen in mammalian and avian hearts (Wang et al, 2003).

Respiratory

   All reptiles breathe using lungs. Aquatic turtles have developed more
   permeable skin, and even gills in their anal region, for some species
   (Orenstein, 2001). Even with these adaptations, breathing is never
   fully accomplished without lungs. Lung ventilation is accomplished
   differently in each main reptile group. In squamates the lungs are
   ventilated almost exclusively by the axial musculature. This is also
   the same musculature that is used during locomotion. Because of this
   constraint, most squamates are forced to hold their breath during
   intense runs. Some, however, have found a way around it. Varanids, and
   a few other lizard species, employ buccal pumping as a complement to
   their normal "axial breathing." This allows the animals to completely
   fill their lungs during intense locomotion, and thus remain aerobically
   active for a long time. Tegu lizards are known to possess a proto-
   diaphragm, which separates the pulmonary cavity from the visceral
   cavity. While not actually capable of movement, it does allow for
   greater lung inflation, by taking the weight of the viscera off the
   lungs (Klein et al, 2003). Crocodilians actually have a muscular
   diaphragm that is analogous to the mammalian diaphragm. The difference
   is that the muscles for the crocodilian diaphragm pull the pubis (part
   of the pelvis, which is movable in crocodilians) back, which brings the
   liver down, thus freeing space for the lungs to expand. This type of
   diaphragmatic setup has been referred to as the "hepatic piston."

   How Turtles & Tortoises breathe has been the subject of much study. To
   date, only a few species have been studied thoroughly enough to get an
   idea of how turtles do it. The results indicate that turtles &
   tortoises have found a variety of solutions to this problem. The
   problem is that most turtle shells are rigid and do not allow for the
   type of expansion and contraction that other amniotes use to ventilate
   their lungs. Some turtles such as the Indian flapshell (Lissemys
   punctata) have a sheet of muscle that envelopes the lungs. When it
   contracts, the turtle can exhale. When at rest, the turtle can retract
   the limbs into the body cavity and force air out of the lungs. When the
   turtle protracts its limbs, the pressure inside the lungs is reduced,
   and the turtle can suck air in. Turtle lungs are attached to the inside
   of the top of the shell (carapace), with the bottom of the lungs
   attached (via connective tissue) to the rest of the viscera. By using a
   series of special muscles (roughly equivalent to a diaphragm), turtles
   are capable of pushing their viscera up and down, resulting in
   effective respiration, since many of these muscles have attachment
   points in conjunction with their forelimbs (indeed, many of the muscles
   expand into the limb pockets during contraction). Breathing during
   locomotion has been studied in three species, and they show different
   patterns. Adult female green sea turtles do not breathe as they crutch
   along their nesting beaches. They hold their breath during terrestrial
   locomotion and breathe in bouts as they rest. North American box
   turtles breathe continuously during locomotion, and the ventilation
   cycle is not coordinated with the limb movements (Landberg et al.,
   2003). They are probably using their abdominal muscles to breathe
   during locomotion. The last species to have been studied is red-eared
   sliders, which also breathe during locomotion, but they had smaller
   breaths during locomotion than during small pauses between locomotor
   bouts, indicating that there may be mechanical interference between the
   limb movements and the breathing apparatus. Box turtles have also been
   observed to breathe while completely sealed up inside their shells
   (ibid).

   Most reptiles lack a secondary palate, meaning that they must hold
   their breath while swallowing. Crocodilians have evolved a bony
   secondary palate that allows them to continue breathing while remaining
   submerged (and protect their brains from getting kicked in by
   struggling prey). Skinks (family Scincidae) also have evolved a bony
   secondary palate, to varying degrees. Snakes took a different approach
   and extended their trachea instead. Their tracheal extension sticks out
   like a fleshy straw, and allows these animals to swallow large prey
   without suffering from asphyxiation.

   Also, crocodiles are known to cry while eating. Many myths and folklore
   have grown around this astonishing fact, such as that the crocodile
   feels guilty for eating, but in truth, the crocodile cries to release
   fluid from its body, to make room for oxygen. This is also due to the
   fact that the crocodile's nasal cavity (nose) is exceptionally small.

Excretion

   Excretion is performed mainly by two small kidneys. In diapsids uric
   acid is the main nitrogenous waste product; turtles, like mammals,
   mainly excrete urea. Unlike the kidneys of mammals and birds, reptile
   kidneys are unable to produce liquid urine more concentrated than their
   body fluid. This is because they lack a specialised structure present
   in the nephrons of birds and mammals, called a Loop of Henle. Because
   of this, many reptiles use the colon and cloaca to aid in the
   reabsorption of water. Some are also able to take up water stored in
   the bladder. Excess salts are also excreted by nasal and lingual
   salt-glands in some reptiles.

Nervous

   Advanced nervous system compared to amphibians. They have twelve pairs
   of cranial nerves.

Sexual

   Most reptiles reproduce sexually. All male reptiles except turtles and
   tortoises have a twin tube like sexual organ called the hemipenes.
   Turtles and tortoises have a single penis. All testudines lay eggs,
   none are live bearing as some lizard and snakes are. All reproductive
   activity occurs with the cloaca, the single exit/entrance at the base
   of the tail where waste and reproduction happens.

   Asexual reproduction has been identified in squamates in six families
   of lizards and one snake. In some species of squamates, a population of
   females are able to produce a unisexual diploid clone of the mother.
   This asexual reproduction called parthenogenesis occurs in several
   species of gecko, and is particularly widespread in the teiids
   (especially Aspidocelis) and lacertids ( Lacerta). Parthenogentic
   species are also suspected to occur among chameleons, agamids,
   xantusiids, and typhlopids.

   Amniotic eggs are covered with leathery or calcareous shells. An
   amnion, chorion and allantois are present during embryonic life. There
   are no larval stages of development.

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