American Museum of Natural History: Reptiles
ANATOMY
Reptiles, the group that gave rise through evolution to birds and mammals, have the same basic body structure as those higher vertebrates. Yet just as birds and mammals changed from their reptilian ancestors, reptiles themselves underwent great changes over their millions of years of existence. This exhibit shows some anatomical features of the reptilian body and shows how structures differ among major groups of reptiles.
RETICULATED PYTHON (Python reticulatus)
Typically, snakes have a greatly elongated body and lack limbs. Some snakes such as this python (see partial skeleton) retain vestiges of the hind limbs, however. This skeleton is 7 meters (23 feet) long. Its 321 vertebrae in the body and 91 in the tail number close to the maximum known in snakes; individuals of some species may have fewer than 130 vertebrae. (Human beings have only 24.) A snake does not add vertebrae and ribs as it grows, but has its full amount before it is born or hatched.
KOMODO DRAGON LIZARD (Varanus komodoensis)
AMERICAN ALLIGATOR (Alligator mississippiensis)
These basically similar skeletons differ in many details evident only on close examination. As an aquatic animal, the alligator has a somewhat high, flattened tail for swimming and relatively small legs and feet. The land-dwelling Dragon has a more rounded tail and larger, more powerful legs. The large, heavy skull of the alligator would be a burden on land but is supported by the water. Another difference in these skeletons is the presence of abdominal ribs (gastralia) in the Alligator.
SKIN
Skin, the outermost covering, protects the body from micro-organisms, poisons and physical damage, retains fluids and minerals, and provides structural support. Its sensory receptors receive stimuli (eg, touch, temperature) from the environment, and it maintains the colors and some structural modifications of the species.
Reptile skin typically consists of rows of raised, hardened scales usually connected by soft, flexible tissue. The outermost layer (epidermis) of the skin forms the hard (keratinized) part of the scales. Such scales differ from fish scales, which form in a different part (dermis) of the skin. Amphibians, unlike reptiles, lack epidermal scales and usually maintain a moist skin that may function in respiration. Reptile skin lacks the feathers and hair that characterize birds and mammals, respectively.
Extensive use of reptile skins for purses, shoes and other leather products has led to massive slaughter, especially of crocodilians. Consequently, the survival of many species is endangered.
SKIN STRUCTURE
This cross-section of lizard skin shows two overlapping scales (350X). Important features are:
EPIDERMIS: Outermost skin layer. Its germinative cells produce daughter cells that move outward and transform into the hard, protective outer scale surface through the process of keratinization. Keratin is a strong protein in epidermal derivatives such as claws, fingernails and beaks. Periodically, the keratinized layer is shed and replaced (Growth and Longevity exhibit, Case 2).
DERMIS: Deeper, thicker skin layer, composed chiefly of fibrous connective tissue. Most pigment cells lie within the dermis. Most blood vessels (not shown) are in both the dermis and epidermis.
HINGE REGION: This area with loose folds allows distension of the skin between the keratinized scales.
SCALE TYPES
Reptile scales vary in size, shape and number according to location on the body. For example, in most snakes the scales on the belly (ventral scutes) are enlarged transversely and are important in locomotion. These differ distinctly from the scales on the back.
Reptiles inherit their basic scale pattern, though temperature during embryonic development may influence scale size and number. Comparison of distantly related species reveals a wide variety of scale types. This diversity probably reflects adaptations for various functions, such as body water balance and reception of solar radiation. The lizards here illustrate various reptile scales.
OSTEODERMS
The deep layer of the skin (dermis) in many kinds of lizards, all crocodilians and on the legs and tails of some turtles contains discs or nodules of protective bone. Often these exist in rows corresponding to those of the outer epidermal scales. Nearly all surfaces of the South American Caiman, Caiman crocodilus, whose skin is shown here, are protected by osteoderms, which appear as numerous light patches on the x-ray photograph (claws and bones of the skull are light also).
COLOR CHANGE
In some lizards, particularly True Chameleons of the Old World and Anoles (American Chameleons) of the New World, individuals can change color completely and rapidly. Color change is stimulated by various factors, including excitement, temperature, lighting, and shade of the background behind the animal.
The Green Anole, Anolis carolinensis, shown here can change from brown to brilliant green, or vice versa, in a matter of minutes. Cross-sections (1,000X) show how color change is caused by movement of pigment within melanophores (brown pigment cells).
BROWN PHASE:
Brown pigment is dispersed upward throughout the fingerlike projections of the melanophores, giving the animal a brown appearance.
GREEN PHASE:
Granules of brown pigment are withdrawn in the melanophores. Now, rays of light penetrate to the iridophores, which reflect blue wavelengths. Reflected blue light passes upward through the yellow pigments of the xanthophores, producing the appearance of green.
TURTLE SHELLS
The shell, which may include up to 30 percent of a turtle's weight, is mostly bone, overlaid by skin. The large, hard plates conspicuous on most turtle shells are keratinized epidermal scales (scutes). The shell's bone forms by fusion of ossified structures in the deep skin (dermis) with vertebrae, ribs, and pectoral and pelvic girdles.
The epidermal scales of the upper shell (carapace) of this Snapping Turtle, Chelydra serpentina, are removed from the left side to reveal the bones beneath. Sutures between scales and those between underlying bones are not directly aligned, a feature which may result in greater strength.
American Museum of Natural History: Reptiles
ANATOMY
Reptiles, the group that gave rise through evolution to birds and mammals, have the same basic body structure as those higher vertebrates. Yet just as birds and mammals changed from their reptilian ancestors, reptiles themselves underwent great changes over their millions of years of existence. This exhibit shows some anatomical features of the reptilian body and shows how structures differ among major groups of reptiles.
RETICULATED PYTHON (Python reticulatus)
Typically, snakes have a greatly elongated body and lack limbs. Some snakes such as this python (see partial skeleton) retain vestiges of the hind limbs, however. This skeleton is 7 meters (23 feet) long. Its 321 vertebrae in the body and 91 in the tail number close to the maximum known in snakes; individuals of some species may have fewer than 130 vertebrae. (Human beings have only 24.) A snake does not add vertebrae and ribs as it grows, but has its full amount before it is born or hatched.
KOMODO DRAGON LIZARD (Varanus komodoensis)
AMERICAN ALLIGATOR (Alligator mississippiensis)
These basically similar skeletons differ in many details evident only on close examination. As an aquatic animal, the alligator has a somewhat high, flattened tail for swimming and relatively small legs and feet. The land-dwelling Dragon has a more rounded tail and larger, more powerful legs. The large, heavy skull of the alligator would be a burden on land but is supported by the water. Another difference in these skeletons is the presence of abdominal ribs (gastralia) in the Alligator.
SKIN
Skin, the outermost covering, protects the body from micro-organisms, poisons and physical damage, retains fluids and minerals, and provides structural support. Its sensory receptors receive stimuli (eg, touch, temperature) from the environment, and it maintains the colors and some structural modifications of the species.
Reptile skin typically consists of rows of raised, hardened scales usually connected by soft, flexible tissue. The outermost layer (epidermis) of the skin forms the hard (keratinized) part of the scales. Such scales differ from fish scales, which form in a different part (dermis) of the skin. Amphibians, unlike reptiles, lack epidermal scales and usually maintain a moist skin that may function in respiration. Reptile skin lacks the feathers and hair that characterize birds and mammals, respectively.
Extensive use of reptile skins for purses, shoes and other leather products has led to massive slaughter, especially of crocodilians. Consequently, the survival of many species is endangered.
SKIN STRUCTURE
This cross-section of lizard skin shows two overlapping scales (350X). Important features are:
EPIDERMIS: Outermost skin layer. Its germinative cells produce daughter cells that move outward and transform into the hard, protective outer scale surface through the process of keratinization. Keratin is a strong protein in epidermal derivatives such as claws, fingernails and beaks. Periodically, the keratinized layer is shed and replaced (Growth and Longevity exhibit, Case 2).
DERMIS: Deeper, thicker skin layer, composed chiefly of fibrous connective tissue. Most pigment cells lie within the dermis. Most blood vessels (not shown) are in both the dermis and epidermis.
HINGE REGION: This area with loose folds allows distension of the skin between the keratinized scales.
SCALE TYPES
Reptile scales vary in size, shape and number according to location on the body. For example, in most snakes the scales on the belly (ventral scutes) are enlarged transversely and are important in locomotion. These differ distinctly from the scales on the back.
Reptiles inherit their basic scale pattern, though temperature during embryonic development may influence scale size and number. Comparison of distantly related species reveals a wide variety of scale types. This diversity probably reflects adaptations for various functions, such as body water balance and reception of solar radiation. The lizards here illustrate various reptile scales.
OSTEODERMS
The deep layer of the skin (dermis) in many kinds of lizards, all crocodilians and on the legs and tails of some turtles contains discs or nodules of protective bone. Often these exist in rows corresponding to those of the outer epidermal scales. Nearly all surfaces of the South American Caiman, Caiman crocodilus, whose skin is shown here, are protected by osteoderms, which appear as numerous light patches on the x-ray photograph (claws and bones of the skull are light also).
COLOR CHANGE
In some lizards, particularly True Chameleons of the Old World and Anoles (American Chameleons) of the New World, individuals can change color completely and rapidly. Color change is stimulated by various factors, including excitement, temperature, lighting, and shade of the background behind the animal.
The Green Anole, Anolis carolinensis, shown here can change from brown to brilliant green, or vice versa, in a matter of minutes. Cross-sections (1,000X) show how color change is caused by movement of pigment within melanophores (brown pigment cells).
BROWN PHASE:
Brown pigment is dispersed upward throughout the fingerlike projections of the melanophores, giving the animal a brown appearance.
GREEN PHASE:
Granules of brown pigment are withdrawn in the melanophores. Now, rays of light penetrate to the iridophores, which reflect blue wavelengths. Reflected blue light passes upward through the yellow pigments of the xanthophores, producing the appearance of green.
TURTLE SHELLS
The shell, which may include up to 30 percent of a turtle's weight, is mostly bone, overlaid by skin. The large, hard plates conspicuous on most turtle shells are keratinized epidermal scales (scutes). The shell's bone forms by fusion of ossified structures in the deep skin (dermis) with vertebrae, ribs, and pectoral and pelvic girdles.
The epidermal scales of the upper shell (carapace) of this Snapping Turtle, Chelydra serpentina, are removed from the left side to reveal the bones beneath. Sutures between scales and those between underlying bones are not directly aligned, a feature which may result in greater strength.