Zoology Herpetology is the study of reptiles and amphibians. A. Life on Land a. While amphibians are able to come on land, their shell-less eggs, thin, moist skin, and gilled larvae prevent most from ever being fully terrestrial. b. Reptiles were the first animals adapted to life entirely on land. i. They gained the title the first fully terrestrial vertebrates because they do not need water to reproduce. Reproduction without water is accomplished by a structure called the amniotic egg. Animals with an amniotic egg are called amniotes. 1. The amniotic egg is different from fish and amphibian eggs because they have four extra membranes: a. Amnion- thin membrane enclosing the fluid in which the embryo floats. This fluid serves to cushion the embryo and prevent dehydration. b. Allantois- stores metabolic wastes produced by the embryo. c. Yolk Sac- encloses the yolk, a fat-rich food supply for the developing embryo. d. Chorion- outermost membrane of the egg; surrounds all other membranes. Helps protect embryo and allows oxygen to enter egg while removing carbon dioxide. 2. Reptile eggs also contain albumen, which is additional protein and water; this is like the egg white of a chicken egg. 3. Most amniotic eggs are surrounded by a mineralized but often flexible shell. Reptile egg shells are described as being leathery, while bird eggs are hardened. Most mammals lack shelled eggs. a. To help reptiles breaking open their shell to hatch, many have a horny tooth on their snout. The tooth drops off shortly after hatching. B. History a. Reptiles evolved from amphibians during the Carboniferous Period and displaced amphibians in many environments. b. The first reptiles, called stem reptiles, gave rise to several other lineages, each of which The term adapted to a different way of “non-avian reptiles” life. refers to a paraphyletic i. Reptiles as form a group (circled) that includes paraphyletic group the living turtles, lizards, snakes, because they do not tuataras, and crocodilians, and a include all descendants number of extinct groups, including of their most recent ichthyosaurs, pterosaurs, and dinosaurs. ancestor. c. The Mesozoic Era (245 to 65 million years ago) is often called the “Age of Reptiles”; This is when reptiles were most diversified and dominant. C. Adaptations of Reptiles a. Amphibians and reptiles are both poikilothermic ectothermic tetrapods, relying on the environment for adjustment of their body temperature. However, there are several adaptations (in addition to the amniotic egg) which distinguish reptiles and make them better suited to land: i. Better developed lungs; reptiles lungs have more surface area than the lungs of amphibians and are ventilated by drawing air into the lungs by expanding the rib cage (lizards and snakes), or moving internal organs (turtles and crocodiles). ii. Tough, dry scaly skin that offers protection against desiccation (drying out) and physical injury. 1. Skin has a keratinized epidermis and a thick, collagen-rich dermis with chromatophores for color and lipids to prevent drying out. 2. Reptiles have a unique form of keratin called beta keratin to provide additional protection. iii. Most reptiles have a three-chambered heart and double loop blood circulation. 1. However, crocodilians which require more energy and oxygen, have a fourchambered heart. a. Pulmonary loop- blood goes from heart to lungs (to pick up oxygen) back to heart b. Systemic loop- blood goes from heart to body (to deliver oxygen) back to heart iv. Reptiles have efficient excretory systems for water conservation. 1. Paired kidneys excrete uric acid as the main nitrogenous waste. 2. Water is resorbed in the bladder so “urine” is often a semisolid mass of uric acid. 3. Salts are removed in many reptiles by salt glands, located near the nose, eyes, or tongue. v. Complex brain with an enlarged cerebrum, used to interpret sensory information and control muscles during movement. vi. The reptilian skeleton differs from other vertebrates in various ways: 1. Reptiles have several bones in their lower jaw that enable them greater bite mobility. 2. Reptiles have only one bone in each ear (the stapes). Mammals have three. 3. Reptiles also have only one occipital condyle (a protrusion on the skull that forms a joint that enables movement of the head) while mammals and amphibians have two occipital condyles. 4. Skull structure also varies among reptiles and other vertebrates. There are three main skull designs: a. Anapsid: Have no openings behind eye socket; Seen in turtles. b. Synapsid: Has a single opening, called a fenestra, behind eye socket. Seen in mammals. c. Diapsid: Have two fenestrae behind eye socket. Seen in all reptiles (except turtles) and birds. vii. Sexes separate (Dioecious) with internal fertilization. 1. Like amphibians, reptiles have a cloaca- a single opening where all waste matter as well as reproductive materials exit the body. 2. Most male reptiles have two copulatory organs called hemipenes; although they only use one at a time. They are housed internally in males just at the base of the tail, and are everted when needed. 3. Unlike many other reptiles, alligators use a penis that is always erect and pops out of their bodies to mate. 4. Visible differences between male and female reptiles are often subtle and reproductive organs are inside their bodies, as a result, it is often difficult to tell if you have a male or female reptile with just a glance. D. Classification a. Reptiles are members of Kingdom Animalia, Phylum Chordata, Subphylum Vertebrata, Class Reptilia b. Of the 16 orders of reptiles known to have existed, there are four living orders of Reptiles today (nearly 8,000 species): i. Order Testudines (Chelonia): Turtles ii. Order Squamata 1. Suborder Sauria: Lizards 2. Suborder Serpentes: Snakes iii. Order Crocodilia: Crocodiles and Alligators iv. Order Rhynchocephalia (Sphenodonta): Tuataras E. Turtles: Order Testudines (Chelonia) a. The terms “turtle,” “tortoise,” and “terrapin” are applied variously to different members of the turtle order. In North America: i. Turtles are usually water-dwelling and have streamlined, disk-shaped shells and webbed feet or flippers to rapidly move in water. They swim, but they also climb out onto banks, logs, or rocks to bask in the sun. In cold weather, they may burrow into the mud, where they go into torpor until spring brings warm weather again. b. c. d. e. f. g. ii. Tortoises are land-dwelling and tend to have dome-shaped shell to retract their head & limbs. They have thick sturdy legs and feet for moving on land and eats lowgrowing shrubs, grasses, and even cactus. Land tortoises are slow; some of them walk at only 0.5 miles per hour. Tortoises that live in hot, dry habitats use their strong forelimbs to dig burrows. Then, when it’s too hot in the sun, they slip underground. iii. Terrapins spend their time both on land and in water, and live along rivers, ponds, and lakes. Terrapins are often found in brackish, swampy areas. Turtles appear in the fossil record in the Triassic Period, some 200 million years ago; they have survived to the present with very little change to their early morphology. The success of this group is attributed to their basic, yet successful, body design consisting of a shell covering the body. i. The dorsal surface of the shell is called the carapace; the ventral surface is the plastron. Both are joined by a bony bridge. ii. The shell is composed of two layers: an outer layer of keratin and an inner layer of bone. The bony layer is fused to the ribs and vertebrae inside the shell. Lacking teeth, a turtle’s jaw is composed of tough, keratinized plates forming a beak, used for gripping food. A turtle’s brain, like that of other reptiles, is small, never exceeding 1% of body weight. The cerebrum, however, is larger than that of an amphibian, and turtles are able to learn a maze about as quickly as a rat. Turtles have poor hearing but a good sense of smell, acute vision, and color perception. Turtles are oviparous. i. Fertilization is internal and all turtles, even marine forms, bury their shelled, amniotic eggs in the ground. ii. Turtles are very careful while constructing their nest, but once eggs are deposited and covered, the female deserts them. iii. An interesting feature of turtle reproduction is that in some turtle families, as in all crocodilians and some lizards, nest temperature determines sex of the hatchlings. 1. In turtles, low temperatures during incubation produce males and high temperatures produce females. h. Turtle Statistics i. Leatherback sea turtles, Dermochelys coriacea, are the largest turtles on Earth, growing up to seven feet (two meters) long and exceeding 2,000 pounds. They are also one of the most migratory, crossing both the Atlantic and Pacific Oceans from their nesting beaches to feed on jellyfish. They are also the fastest turtle, swimming up to 22 miles per hour. ii. The alligator snapping turtle, Macroclemys temminckii, is the biggest freshwater turtle in North America. It can grow to 2.5 feet long, can weigh as much as 200 pounds. It has powerful jaws, a hooked beak, sharp claws, and a muscular tail. The alligator snapping turtle does eat some aquatic plants, but it's mostly a carnivore that dines on a variety of fish, frogs, snakes, worms, clams, crayfish and even other turtles. It catches many of its prey using an appendage on its tongue that it can wiggle to look like a worm. iii. The African helmeted turtle, Pelomedusa subrufa, is the most widespread turtle species in Africa. It's a hunter-scavenger that hunts in packs and seems happy to eat most anything, from parasites lodged in the skin of rhinoceroses to young birds and small mammals. It is well known for its terrible smell; it has four glands, one under each leg, which release a foul-smelling liquid seems to repulse horses as well as humans. F. Lizards & Snakes: Order Squamata a. Lizards appeared in the fossil record as early as the Jurassic. Snakes probably evolved from lizards during the Cretaceous period. b. Snakes and lizards have a kinetic skull, which means it is modified to have movable joints, specialized for eating large prey. i. In snakes, the two halves of the lower jaw (mandibles) are joined only by muscles and skin, allowing them to spread widely apart. ii. Since a snake must keep breathing during the slow process of swallowing, its tracheal opening (glottis) is thrust forward between the two mandibles. iii. Swallowing may take several hours but saliva begins digestion during swallowing. c. Snakes: i. Snakes are limbless and usually lack both pectoral and pelvic girdles; well known for their extreme elongation of their body and accompanying displacement and rearrangement of internal organs. ii. The cornea of a snake’s eye, lacking a movable eyelid, is permanently protected with a transparent membrane called a spectacle, which, together with reduced eyeball mobility, gives snakes the cold, unblinking stare that many people find frightening. iii. Most snakes have relatively poor vision. iv. Snakes have no external ears or tympanic membrane, but are quite sensitive to vibrations carried in the ground. v. The olfactory areas in the nose are not well developed but they detect chemicals (smell/taste) using their forked tongues and Jacobson’s organs (pit-like organs in the roof of the mouth). vi. Despite their lack of limbs, snakes have evolved different ways of moving: 1. Lateral undulations a. Most common; Head moves side to side causing wave of muscular contractions and forwards movement in an S-shaped path. 2. Rectilinear Movements a. A muscular force is applied to the belly so scutes or scales on the belly catch on rough surfaces allowing the snake to moves forward slowly. 3. Sidewinding a. A sideways movement of body; used by some desert snakes. The head is vigorously flung from side to side; this whiplike motion moves body along. vii. Snakes have various ways of killing their prey: 1. Constrictors wrap body around prey & squeeze them to death. Common constrictors include boas, pythons, and anacondas. 2. Snakes may inject venom: a. Venomous snakes include Cobra, Viper, Copperhead, Rattle snake. b. Water moccasin & rattlesnake use Hemotoxin; poisonous proteins that attack red blood cells. c. Copperheads use Neurotoxin; poison that works on nervous system affecting heart rate & breathing. d. Venomous snakes can have one of 3 types of fangs: i. Rear-fanged snakes, such as the boomsland, bite prey & use grooved back teeth to guide venom into puncture wound. ii. Front-fanged snakes, such as cobra, inject poison through 2 small front fangs that act like a hypodermic needle. iii. Hinged- fang snakes, such as rattlesnake, water moccasin, and copperhead, have hinged fangs in roof of mouth that swing forward to inject poison. d. Lizards (Suborder Sauria) i. With about 3,000 species of lizards alive today, about half of the world's living reptile species are lizards. ii. Most lizards have movable eyelids. iii. Lizards often rely on speed, agility, & camouflage to catch prey, including insects and small worms. iv. For protection, lizards may use active displays such as squirting blood, hissing, or inflating bodies. Some show autotomy- breaking off their tail to escape predators. v. Lizards are an extremely diverse group, including terrestrial, burrowing, aquatic, arboreal, and aerial members. 1. Geckos: small, agile, mostly nocturnal forms with adhesive toe pads that enable them to walk upside down and on vertical surfaces. 2. Iguanas: often brightly colored with ornamental crests, frills, and throat fans, and the remarkable marine iguana of the Galápagos Islands. 3. Skinks: have elongate bodies, an armor of tight-fitting osteoderms, and reduced limbs in many species 4. Monitors: large, active predators that include the largest lizard, the Komodo dragon. 5. Chameleons: a group of arboreal lizards, mostly of Africa and Madagascar. Chameleons catch insects with a sticky-tipped tongue that can be projected accurately and rapidly to a distance greater than the length of their body. Also can change colors for protection. 6. Legless lizards: a few such as glass lizards are completely limbless. 7. Venomous lizards: Gila monsters, and their close relatives, beaded lizards, are the only lizards capable of delivering a venomous bite. G. Crocodilians: Order Crocodilia a. Crocodilians are large, aquatic reptiles; of the living reptiles, they are the most closely related to dinosaurs. i. Modern crocodilians are the only surviving reptiles of the archosaurian lineage that gave rise to the great Mesozoic radiation of dinosaurs and birds. They also differ little in structural details from primitive crocodilians of the early Mesozoic. b. Live in tropical and subtropical regions around world and can usually be distinguished based on head morphology: i. Crocodiles are tropical or subtropical, usually nocturnal, reptiles found in Africa, Asia, South America, & extreme southern Florida. 1. Long triangle-shaped heads; when mouth is closed you can see the upper and lower teeth showing; teeth vary in size. ii. Two species of alligators are found in China & the southern United States. 1. Wide flat heads with round noses; When mouth is closed only the upper teeth are showing; Teeth vary in size. 2. Alligators are usually less aggressive than crocodiles and far less dangerous to humans. iii. Caimans are native to Central America and South America but have been introduced in Florida; they resemble alligators. iv. Gavials (aka Gharials) live only in India & Burma. 1. They are fish eating reptiles with very slender, long snouts. Males have a conspicuous knob at the tip of their snout. c. All are aggressive carnivores. d. Usually capture prey by floating just beneath the surface of water near shore and exploding out of water when an animal comes to drink. When they seize the prey they bring them back into the water to drown and eat them. i. A unique adaptation found in crocodilians and mammals, is a complete secondary palate. This innovation pushed the internal nares to the posterior, allowing a crocodilian to breathe when its mouth is filled with water or food. e. Reproduction i. Male alligators make loud bellows during the mating season. ii. Alligators and crocodiles are oviparous. Usually 20 to 50 eggs are laid in a mass of dead vegetation or buried in the sand and guarded by the mother. The mother hears vocalizations from hatching young and responds by opening the nest to allow the hatchlings to escape. Unlike other reptiles, crocodilians care for young after hatching. iii. As with many turtles and some lizards, incubation temperature of the eggs determines sex ratio of the offspring. However, unlike turtles low nest temperatures produce only females, whereas high nest temperatures produce only males. H. Tuataras: Order Rhynchocephalia (Sphenodonta) a. Tuataras are nocturnal, lizard-like reptiles that live in burrows often shared with petrels. They usually hide in burrows during the day and feed on insects, worms, and other small animals at night. b. Unlike most reptiles, they are most active at lower temperatures. c. Tuatara means “spiny crest” in native New Zealand language; they have this spiny crest running down center of their back. d. Tuataras bear a well-developed median parietal eye complete with elements of cornea, lens, and retina; although since it is buried beneath opaque skin this “third eye” can register only changes in light intensity. e. Only 2 living species; both inhabit only a few small islands of New Zealand. i. They were once widespread throughout the two main islands of New Zealand humans introduced nonnative animals, including rats, cats, dogs, and goats, which prey upon tuataras and their eggs. f. Tuataras are particularly vulnerable because they have slow growth and low reproductive rates. i. These slow-growing animals can live long lives; one is recorded to have lived 77 years. ii. Reproduction- Lay about a dozen eggs in a burrow. Take up to 1-1¼ years to hatch. No parental care.
