1. 26-1 CHAPTER 26 Amniote Origins and Nonavian Reptiles Amniote Origins and Nonavian Reptiles

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3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-3 Diversity Amniotic “Pond” Any animal with a shell-less egg remains tied to water Any animal with a shell-less egg remains tied to water Development of a shelled egg freed the reptilian groups to exploit land Development of a shelled egg freed the reptilian groups to exploit land Extraembryonic membranes from previous evolutionary aquatic stages are maintained Extraembryonic membranes from previous evolutionary aquatic stages are maintained Allantois serves as a respiratory surface and a chamber to store nitrogenous wastes Allantois serves as a respiratory surface and a chamber to store nitrogenous wastes Chorion allows O 2 and CO 2 to freely pass Chorion allows O 2 and CO 2 to freely pass Surrounding the organism is a porous, parchment- like or leathery shell Surrounding the organism is a porous, parchment- like or leathery shell

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-4 Amniotes Amniota Amniota Single, monophyletic lineage of Paleozoic tetrapods Single, monophyletic lineage of Paleozoic tetrapods Nonavian reptiles, birds, and mammals Nonavian reptiles, birds, and mammals Developing young enclosed by extraembryonic membrane called the amnion Developing young enclosed by extraembryonic membrane called the amnion Secretes fluid, amniotic fluid, in which embryo/fetus floats Secretes fluid, amniotic fluid, in which embryo/fetus floats Diversity

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-5 Diversity Members of the paraphyletic class Reptilia includes nearly 8000 species Members of the paraphyletic class Reptilia includes nearly 8000 species Approximately 340 occur in the U.S. and Canada Approximately 340 occur in the U.S. and Canada The Age of Reptiles lasted over 165 million years and included the dinosaurs The Age of Reptiles lasted over 165 million years and included the dinosaurs A mass extinction occurred at the end of the Mesozoic A mass extinction occurred at the end of the Mesozoic Modern reptiles represent surviving lineages Modern reptiles represent surviving lineages Tuatara is the sole survivor of a group that otherwise disappeared 100 million years ago Tuatara is the sole survivor of a group that otherwise disappeared 100 million years ago Lizards and snakes radiated into diverse and abundant groups Lizards and snakes radiated into diverse and abundant groups Diversity

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-6 Origin and Early Evolution of Amniotes History Amniotes arose from amphibian-like tetrapods, the anthracosaurs, during the Carboniferous Amniotes arose from amphibian-like tetrapods, the anthracosaurs, during the Carboniferous By the late Carboniferous, skulls of amniotes could be separated into groups based on three patterns of openings (fenestra) in the temporal region By the late Carboniferous, skulls of amniotes could be separated into groups based on three patterns of openings (fenestra) in the temporal region Anapsids Anapsids Have a skull with no temporal opening behind the orbits Have a skull with no temporal opening behind the orbits Modern turtles Modern turtles

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8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-8 Diapsids Diapsids Gave rise to all other traditional “reptiles” (except turtles) and to birds Gave rise to all other traditional “reptiles” (except turtles) and to birds Skull has two temporal openings Skull has two temporal openings One pair below the cheeks and another above One pair below the cheeks and another above Lepidosaurs Lepidosaurs Ichthyosaurs and living reptiles, including lizards and snakes Ichthyosaurs and living reptiles, including lizards and snakes Archosaurs Archosaurs Includes dinosaurs, living crocodilians, and birds Includes dinosaurs, living crocodilians, and birds Sauropterygians Sauropterygians Includes extinct aquatic groups including the long-necked plesiosaurs Includes extinct aquatic groups including the long-necked plesiosaurs Origin and Early Evolution of Amniotes

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10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-10 Synapsids Synapsids Mammal-like reptiles with a single pair of temporal openings low on the cheeks Mammal-like reptiles with a single pair of temporal openings low on the cheeks These openings are associated with large muscles that elevate the lower jaw These openings are associated with large muscles that elevate the lower jaw Changes in jaw musculature Changes in jaw musculature Might reflect a shift from suction feeding in aquatic vertebrates to terrestrial feeding Might reflect a shift from suction feeding in aquatic vertebrates to terrestrial feeding Required larger muscles to produce static pressure Required larger muscles to produce static pressure Functional significance of the evolution of temporal openings in amniotes is not fully understood Functional significance of the evolution of temporal openings in amniotes is not fully understood Origin and Early Evolution of Amniotes

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-11 Derived Characters of Amniotes Amniotic egg All amniotes have eggs with four extraembryonic membranes All amniotes have eggs with four extraembryonic membranes Amnion, allantois, chorion, and yolk sac Amnion, allantois, chorion, and yolk sac Amnion Amnion Encloses the embryo in fluid-filled space Encloses the embryo in fluid-filled space Cushions the embryo and provides an aqueous medium for growth Cushions the embryo and provides an aqueous medium for growth Allantois Allantois Stores metabolic wastes Stores metabolic wastes Origin and Early Evolution of Amniotes

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13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-13 Chorion Chorion Surrounds embryo and all other extraembryonic membranes Surrounds embryo and all other extraembryonic membranes Lies just beneath shell Lies just beneath shell Highly vascularized Highly vascularized Respiratory surface Respiratory surface Allantois and chorion sometimes fuse to form respiratory structure: chorioallantoic membrane Allantois and chorion sometimes fuse to form respiratory structure: chorioallantoic membrane Yolk sac Yolk sac Nutrient storage Nutrient storage Origin and Early Evolution of Amniotes

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-14 Amniotic egg permitted development of a larger, faster-growing embryo Amniotic egg permitted development of a larger, faster-growing embryo One hypothesis suggests that one step in the evolution of the amniotic egg was replacement of the jelly layer with a shell One hypothesis suggests that one step in the evolution of the amniotic egg was replacement of the jelly layer with a shell Provided better support and movement of oxygen Provided better support and movement of oxygen Shell could also be broken down to provide calcium for growing skeletal structures Shell could also be broken down to provide calcium for growing skeletal structures All amniotes All amniotes Lack gilled larvae and have internal fertilization Lack gilled larvae and have internal fertilization Eliminated the need for aquatic environments Eliminated the need for aquatic environments Penis is the most common copulatory organ Penis is the most common copulatory organ Derived from cloacal wall, appears to be an amniote innovation Derived from cloacal wall, appears to be an amniote innovation Origin and Early Evolution of Amniotes

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-15 Rib ventilation of the lungs Amniotes draw air into lungs by expanding the thoracic cavity using costal muscles or pulling the liver posterior Amniotes draw air into lungs by expanding the thoracic cavity using costal muscles or pulling the liver posterior The shift from positive to negative ventilation probably influenced the evolution of amniotic limbs The shift from positive to negative ventilation probably influenced the evolution of amniotic limbs Early tetrapods used the rib muscles to make lateral undulations producing a wriggling motion Early tetrapods used the rib muscles to make lateral undulations producing a wriggling motion Origin and Early Evolution of Amniotes

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-16 Thicker and more waterproof skin Amniote skin is thick and tends to be more keratinized and less permeable to water Amniote skin is thick and tends to be more keratinized and less permeable to water Variety of structures composed of keratin such as scales, hair, feathers, and claws project from the skin Variety of structures composed of keratin such as scales, hair, feathers, and claws project from the skin Keratin protects the skin from physical trauma, and lipids prevent water loss Keratin protects the skin from physical trauma, and lipids prevent water loss Few amniotes use skin as a primary respiratory organ because keratin and lipids limit exchange of gases Few amniotes use skin as a primary respiratory organ because keratin and lipids limit exchange of gases Origin and Early Evolution of Amniotes

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18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-18 Changes in Traditional Classification of Reptiles Clade Archosauria Clade Archosauria Includes the birds, crocodilians, and the extinct dinosaurs and pterosaurs Includes the birds, crocodilians, and the extinct dinosaurs and pterosaurs Archosaurs along with their sister group the lepidosaurs (lizards and snakes), and turtles form a monophyletic group that cladists call Reptilia Archosaurs along with their sister group the lepidosaurs (lizards and snakes), and turtles form a monophyletic group that cladists call Reptilia The term “nonavian reptiles” refers to a paraphyletic group that includes the living turtles, lizards, snakes, tuataras, and crocodilians, and a number of extinct groups including plesiosaurs, ichthyosaurs, pterosaurs, and dinosaurs The term “nonavian reptiles” refers to a paraphyletic group that includes the living turtles, lizards, snakes, tuataras, and crocodilians, and a number of extinct groups including plesiosaurs, ichthyosaurs, pterosaurs, and dinosaurs Origin and Early Evolution of Amniotes

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-19 Characteristics of Nonavian Reptiles Nonavian reptiles have better developed lungs than amphibians Nonavian reptiles have better developed lungs than amphibians Nonavian lungs have more surface area than amphibians’ lungs Nonavian lungs have more surface area than amphibians’ lungs Nonavian ventilation occurs by drawing air into the lungs rather than pushing air into the lungs Nonavian ventilation occurs by drawing air into the lungs rather than pushing air into the lungs Nonavian reptiles expand the thoracic cavity thus expanding the rib cage in order to draw air in Nonavian reptiles expand the thoracic cavity thus expanding the rib cage in order to draw air in Pulmonary respiration is supplemented by respiration in the cloaca or pharynx in many aquatic turtles and by cutaneous respiration in sea snakes and turtles Pulmonary respiration is supplemented by respiration in the cloaca or pharynx in many aquatic turtles and by cutaneous respiration in sea snakes and turtles

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-20 Nonavian reptiles have tough, dry scaly skin that offers protection against desiccation and physical injury Nonavian reptiles have tough, dry scaly skin that offers protection against desiccation and physical injury Amphibians’ thin, moist skin permits gas exchange Amphibians’ thin, moist skin permits gas exchange Also makes them vulnerable to dehydration Also makes them vulnerable to dehydration Skin of nonavian reptiles has an epidermis of varying thickness and a thick, collagen-rich dermis Skin of nonavian reptiles has an epidermis of varying thickness and a thick, collagen-rich dermis Dermis contains chromatophores Dermis contains chromatophores Color-bearing cells that give many lizards and snakes their colorful hues Color-bearing cells that give many lizards and snakes their colorful hues Characteristics of Nonavian Reptiles

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-21 Resistance to desiccation Resistance to desiccation Provided primarily hydrophobic lipids in epidermis Provided primarily hydrophobic lipids in epidermis Scales of nonavian reptiles Scales of nonavian reptiles Formed mostly of beta keratin and provide protection against wear in terrestrial environments Formed mostly of beta keratin and provide protection against wear in terrestrial environments In crocodilians, scales remain throughout life In crocodilians, scales remain throughout life In other nonavian reptiles such as lizards and snakes, new keratinized epidermis replaces old epidermis which is shed In other nonavian reptiles such as lizards and snakes, new keratinized epidermis replaces old epidermis which is shed Turtles have scutes Turtles have scutes Platelike modified scales Platelike modified scales Crocodiles and many lizards possess osteoderms Crocodiles and many lizards possess osteoderms Bony plates located the dermis beneath scales Bony plates located the dermis beneath scales Characteristics of Nonavian Reptiles

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-22 Amniotic egg of nonavian reptiles Amniotic egg of nonavian reptiles Permits rapid development of large young in relatively dry environments Permits rapid development of large young in relatively dry environments All egg shells of nonavian reptiles are impregnated with calcium All egg shells of nonavian reptiles are impregnated with calcium Turtles have eggs with rigid shells Turtles have eggs with rigid shells All others are leathery All others are leathery In some species of nonavian reptiles In some species of nonavian reptiles Embryo develops in reproductive tract of female Embryo develops in reproductive tract of female Characteristics of Nonavian Reptiles

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-23 Jaws of nonavian reptile Jaws of nonavian reptile Efficiently designed for applying crushing or gripping force to prey Efficiently designed for applying crushing or gripping force to prey Larger jaw muscles have mechanical advantage over the jaws of fishes which are designed for suction feeding or for quick closure Larger jaw muscles have mechanical advantage over the jaws of fishes which are designed for suction feeding or for quick closure Tongue is muscular and mobile Tongue is muscular and mobile Functions to move food in mouth for mastication and swallowing Functions to move food in mouth for mastication and swallowing Characteristics of Nonavian Reptiles

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-24 Nonavian reptiles have an efficient and versatile circulatory system and higher blood pressure than amphibians Nonavian reptiles have an efficient and versatile circulatory system and higher blood pressure than amphibians Right atrium receives deoxygenated blood and is partitioned from the left atrium which receives oxygenated blood Right atrium receives deoxygenated blood and is partitioned from the left atrium which receives oxygenated blood Crocodilians have separated ventricles Crocodilians have separated ventricles In other nonavian reptiles, ventricle is incompletely partitioned into multiple chambers In other nonavian reptiles, ventricle is incompletely partitioned into multiple chambers All nonavian reptiles have two functionally separate circulations All nonavian reptiles have two functionally separate circulations Characteristics of Nonavian Reptiles

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26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-26 Nonavian reptiles have efficient strategies for water conservation Nonavian reptiles have efficient strategies for water conservation Amphibians secrete metabolic waste primarily as ammonia Amphibians secrete metabolic waste primarily as ammonia Ammonia is toxic Ammonia is toxic Must be removed in a dilute solution such as water Must be removed in a dilute solution such as water Nonavian reptiles secrete nitrogenous wastes as uric acid Nonavian reptiles secrete nitrogenous wastes as uric acid Relatively non-toxic Relatively non-toxic Characteristics of Nonavian Reptiles

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-27 All amniotes have metanephric kidneys All amniotes have metanephric kidneys Nonavian reptiles cannot concentrate urine in the kidneys Nonavian reptiles cannot concentrate urine in the kidneys Urinary bladder receives undiluted urine Urinary bladder receives undiluted urine Water and most salts Water and most salts Resorbed in the bladder Resorbed in the bladder “urine” voided as a semisolid mass of uric acid “urine” voided as a semisolid mass of uric acid Salt is removed by salt glands near the nose, eyes, or tongue Salt is removed by salt glands near the nose, eyes, or tongue Characteristics of Nonavian Reptiles

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-28 The nervous system of nonavian reptiles is more complex than that of amphibians The nervous system of nonavian reptiles is more complex than that of amphibians Brain of nonavian reptiles small compared to brain of other amniotes Brain of nonavian reptiles small compared to brain of other amniotes However, cerebrum of all amniotes is relatively enlarged However, cerebrum of all amniotes is relatively enlarged Enlargement of cerebrum correlated with integration of sensory information and muscle control during locomotion Enlargement of cerebrum correlated with integration of sensory information and muscle control during locomotion Nonavian reptiles have good vision Nonavian reptiles have good vision Snakes and many lizards use a highly sensitive sense of smell to find prey and mates Snakes and many lizards use a highly sensitive sense of smell to find prey and mates Olfaction assisted by a Jacobson’s organ, a specialized olfactory chamber in the roof of the mouth Olfaction assisted by a Jacobson’s organ, a specialized olfactory chamber in the roof of the mouth Characteristics of Nonavian Reptiles

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-29 Characteristics and Natural History of Reptilian Orders Order Testudines (Chelonia) Fossils appear in the Upper Triassic, 200 million years ago Fossils appear in the Upper Triassic, 200 million years ago Shells consist of a dorsal carapace and a ventral plastron Shells consist of a dorsal carapace and a ventral plastron Outer horny layer of keratin and an inner layer of bone Outer horny layer of keratin and an inner layer of bone Bony layer is a fusion of ribs, vertebrae, and dermally-ossified elements Bony layer is a fusion of ribs, vertebrae, and dermally-ossified elements Unique among vertebrates, limbs and limb girdles are located deep to the ribs Unique among vertebrates, limbs and limb girdles are located deep to the ribs Lack teeth and use tough, horny plates for gripping food Lack teeth and use tough, horny plates for gripping food

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32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-32 Breathing Breathing Consequence of having a rigid shell Consequence of having a rigid shell Turtle cannot expand chest to breathe Turtle cannot expand chest to breathe Solve problem by using abdominal and pectoral muscles as a “diaphragm” Solve problem by using abdominal and pectoral muscles as a “diaphragm” Air is drawn in by contraction of the limb flank muscles, increasing abdominal cavity volume Air is drawn in by contraction of the limb flank muscles, increasing abdominal cavity volume Exhalation accomplished by drawing back the shoulder girdle to compress the viscera Exhalation accomplished by drawing back the shoulder girdle to compress the viscera These actions are visible as bellows-like movements at the turtle’s “limb pockets” These actions are visible as bellows-like movements at the turtle’s “limb pockets” Movement of limbs while walking also helps ventilate the lungs Movement of limbs while walking also helps ventilate the lungs Some aquatic turtles gain sufficient oxygen by pumping water in and out of the mouth cavity Some aquatic turtles gain sufficient oxygen by pumping water in and out of the mouth cavity Characteristics and Natural History of Reptilian Orders

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-33 Nervous System and Senses Nervous System and Senses Brain is small, less than 1% percent of body weight Brain is small, less than 1% percent of body weight Cerebrum is larger than that of amphibians Cerebrum is larger than that of amphibians Some turtles can learn a path through a maze Some turtles can learn a path through a maze Have a middle and an inner ear but sound perception is poor Have a middle and an inner ear but sound perception is poor Make few sounds aside from those made during mating Make few sounds aside from those made during mating Good sense of smell, acute vision, and color perception about equal to humans Good sense of smell, acute vision, and color perception about equal to humans Characteristics and Natural History of Reptilian Orders

34. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-34 Reproduction and Development Reproduction and Development Oviparous Oviparous Fertilization is internal Fertilization is internal Bury their eggs in the ground Bury their eggs in the ground Female lays her eggs in a nest and deserts them Female lays her eggs in a nest and deserts them In some turtle families nest temperature determines sex of hatchlings In some turtle families nest temperature determines sex of hatchlings Low temperatures produce males Low temperatures produce males High temperatures produce females High temperatures produce females Characteristics and Natural History of Reptilian Orders

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36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-36 Giant Turtles Giant Turtles Buoyed by water, marine turtles may reach two meters long and 725 kilograms in weight Buoyed by water, marine turtles may reach two meters long and 725 kilograms in weight Giant land tortoises, such as those on the Galápagos Islands, weigh several hundred kilograms Giant land tortoises, such as those on the Galápagos Islands, weigh several hundred kilograms Low metabolic activity may explain their longevity, believed to exceed 150 years Low metabolic activity may explain their longevity, believed to exceed 150 years Box Turtles Box Turtles Shell is an effective coat of armor Shell is an effective coat of armor Plastron is hinged Plastron is hinged Pulls the plastron up to fully enclose body Pulls the plastron up to fully enclose body Characteristics and Natural History of Reptilian Orders

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39. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-39 Snapping Turtles Snapping Turtles Have a reduced shell that does not permit full withdrawal of the body Have a reduced shell that does not permit full withdrawal of the body Jaws are adequate defense Jaws are adequate defense Entirely carnivorous and can eat fish, frogs, waterfowl, etc. Entirely carnivorous and can eat fish, frogs, waterfowl, etc. Aquatic but must come ashore to lay eggs Aquatic but must come ashore to lay eggs Characteristics and Natural History of Reptilian Orders

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41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-41 Order Squamata: Lizards and Snakes Most recent and diverse of diaspids Most recent and diverse of diaspids Account for up 95% of living nonavian reptiles Account for up 95% of living nonavian reptiles Lizards appeared in the fossil record in the Permian but did not radiate until the Cretaceous Lizards appeared in the fossil record in the Permian but did not radiate until the Cretaceous Snakes appeared in the late Cretaceous from a group whose descendants include monitor lizards Snakes appeared in the late Cretaceous from a group whose descendants include monitor lizards Characteristics and Natural History of Reptilian Orders

42. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-42 Diaspid skulls have lost dermal bone ventral and posterior to lower temporal opening Diaspid skulls have lost dermal bone ventral and posterior to lower temporal opening Allowed evolution in lizards of a mobile skull with movable joints, a kinetic skull Allowed evolution in lizards of a mobile skull with movable joints, a kinetic skull The quadrate, fused to the skull in other nonavian reptiles, has a joint at the dorsal end and articulates with the lower jaw The quadrate, fused to the skull in other nonavian reptiles, has a joint at the dorsal end and articulates with the lower jaw Joints in palate and across roof of the skull allow snout to be tilted up Joints in palate and across roof of the skull allow snout to be tilted up Allows squamates to seize and manipulate prey and effectively close the jaw with force Allows squamates to seize and manipulate prey and effectively close the jaw with force Characteristics and Natural History of Reptilian Orders

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45. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-45 Exceptional skull mobility of snakes is considered a major factor in their diversification Exceptional skull mobility of snakes is considered a major factor in their diversification Viviparity Viviparity In reptiles, limited to squamates In reptiles, limited to squamates Evolved at least 100 separate times Evolved at least 100 separate times Associated with cold climates Associated with cold climates Increasing the length of time eggs are kept in oviduct Increasing the length of time eggs are kept in oviduct Developing young respire through extraembryonic membranes Developing young respire through extraembryonic membranes Young obtain nutrition from yolk sacs, via the mother, or a combination of both Young obtain nutrition from yolk sacs, via the mother, or a combination of both Characteristics and Natural History of Reptilian Orders

46. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-46 Suborder Sauria: Lizards Diverse group with terrestrial, burrowing, aquatic, arboreal, and some aerial members Diverse group with terrestrial, burrowing, aquatic, arboreal, and some aerial members Geckos Geckos Small, agile, nocturnal forms Small, agile, nocturnal forms Adhesive toe pads allow them to walk on ceilings Adhesive toe pads allow them to walk on ceilings Iguanids Iguanids Include many New World lizards as well as the marine iguana of the Galápagos Include many New World lizards as well as the marine iguana of the Galápagos Chameleons Chameleons Arboreal lizards of Africa and Madagascar Arboreal lizards of Africa and Madagascar Many have an extendible tongue Many have an extendible tongue Characteristics and Natural History of Reptilian Orders

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49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-49 Some have degenerate limbs Some have degenerate limbs Glass lizards are nearly limbless Glass lizards are nearly limbless Movable eyelids whereas snakes have a transparent covering Movable eyelids whereas snakes have a transparent covering Nocturnal geckos have retinas with only rods Nocturnal geckos have retinas with only rods Day-active lizards have both rods and cones Day-active lizards have both rods and cones Have an external ear that snakes lack Have an external ear that snakes lack Geckos use vocal signals to announce territory and drive away males Geckos use vocal signals to announce territory and drive away males Some lizards survive well in hot and dry regions Some lizards survive well in hot and dry regions Characteristics and Natural History of Reptilian Orders

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51. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-51 Conserve water by producing semisolid urine with a high content of crystalline uric acid Conserve water by producing semisolid urine with a high content of crystalline uric acid Some can store fat in tails to provide energy and metabolic water during drought Some can store fat in tails to provide energy and metabolic water during drought Gila monster and beaded lizard are the only lizards capable of a venomous bite Gila monster and beaded lizard are the only lizards capable of a venomous bite Lizards keep body temperature relatively constant by behavioral thermoregulation, although they are ectotherms Lizards keep body temperature relatively constant by behavioral thermoregulation, although they are ectotherms Successful strategy in ecosystems with low productivity and warm climates, such as tropical deserts and grasslands Successful strategy in ecosystems with low productivity and warm climates, such as tropical deserts and grasslands Characteristics and Natural History of Reptilian Orders

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53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-53 Amphisbaenians or “worm lizards” highly specialized for a fossorial (burrowing life) Amphisbaenians or “worm lizards” highly specialized for a fossorial (burrowing life) Until recently, were placed in a separate suborder, Amphisbaenia because they appeared to be so different from other lizards Until recently, were placed in a separate suborder, Amphisbaenia because they appeared to be so different from other lizards Morphological and molecular data show they are highly modified lizards Morphological and molecular data show they are highly modified lizards Have elongate, cylindrical bodies of nearly uniform diameter Have elongate, cylindrical bodies of nearly uniform diameter Lack any trace of limbs Lack any trace of limbs Eyes are usually hidden below skin and there are no external ear openings Eyes are usually hidden below skin and there are no external ear openings Skull is conical or spade-shaped to assist in tunneling Skull is conical or spade-shaped to assist in tunneling Characteristics and Natural History of Reptilian Orders

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55. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-55 Skin is formed in independently-moving rings which can grip the soil Skin is formed in independently-moving rings which can grip the soil Creates a movement similar to earthworms Creates a movement similar to earthworms Found in South America and tropical Africa Found in South America and tropical Africa In the U.S., one species occurs in Florida called the “graveyard snake” In the U.S., one species occurs in Florida called the “graveyard snake” Characteristics and Natural History of Reptilian Orders

56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-56 Suborder Serpentes: Snakes Limbless and have lost pectoral and pelvic girdles (except in pythons) Limbless and have lost pectoral and pelvic girdles (except in pythons) The many vertebrae are shorter and wider than in other tetrapods, allowing undulation The many vertebrae are shorter and wider than in other tetrapods, allowing undulation Elevation of the neural spine gives the musculature more leverage Elevation of the neural spine gives the musculature more leverage Feeding apparatus allows them to eat prey several times their own diameter Feeding apparatus allows them to eat prey several times their own diameter Two halves of lower jaw are loosely joined, allowing them to spread apart Two halves of lower jaw are loosely joined, allowing them to spread apart Skull bones also loosely articulated so mouth can accommodate large prey Skull bones also loosely articulated so mouth can accommodate large prey To allow breathing during the slow process of swallowing, the tracheal opening is extended To allow breathing during the slow process of swallowing, the tracheal opening is extended Characteristics and Natural History of Reptilian Orders

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58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-58 Eyeballs have reduced mobility and a permanent corneal membrane for protection Eyeballs have reduced mobility and a permanent corneal membrane for protection Most have poor vision Most have poor vision Arboreal snakes in tropical forests have highly developed vision Arboreal snakes in tropical forests have highly developed vision Lack external ears and do not respond to most aerial sounds Lack external ears and do not respond to most aerial sounds Can feel vibrations at low frequencies, especially vibrations carried in the ground Can feel vibrations at low frequencies, especially vibrations carried in the ground Chemical senses rather than vision or hearing are main senses used to hunt prey Chemical senses rather than vision or hearing are main senses used to hunt prey Characteristics and Natural History of Reptilian Orders

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60. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-60 Jacobson’s organs Jacobson’s organs Pair of pits in the roof of the mouth Pair of pits in the roof of the mouth Lined with olfactory epithelium Lined with olfactory epithelium Forked tongue picks up scent particles and conveys them to this organ Forked tongue picks up scent particles and conveys them to this organ Skin is infolded between scales Skin is infolded between scales When stretched by a large meal, the skin is unfolded When stretched by a large meal, the skin is unfolded Characteristics and Natural History of Reptilian Orders

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62. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-62 Snake Locomotion Snake Locomotion Lateral undulation Lateral undulation S-shaped movement that pushes against rough ground and water S-shaped movement that pushes against rough ground and water Concertina movement Concertina movement Extension of S-shaped loops to strike or to climb trees Extension of S-shaped loops to strike or to climb trees Rectilinear movement Rectilinear movement Straight movement using minute lifting of consecutive ribs Straight movement using minute lifting of consecutive ribs Sidewinding Sidewinding Sideways looping by desert vipers that “walks” them across loose sand Sideways looping by desert vipers that “walks” them across loose sand Characteristics and Natural History of Reptilian Orders

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64. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-64 Pit vipers, such as rattlesnakes Pit vipers, such as rattlesnakes Have “pits” with nerve endings sensitive to heat emitted by warm-bodied birds and mammals Have “pits” with nerve endings sensitive to heat emitted by warm-bodied birds and mammals Viper fangs are hollow and hinged to inject venom when snake strikes Viper fangs are hollow and hinged to inject venom when snake strikes Of an average of 8,000 snake bites each year in the U.S., only about 12 result in death Of an average of 8,000 snake bites each year in the U.S., only about 12 result in death Nonvenomous snakes Nonvenomous snakes Kill prey by constriction or by biting and swallowing Kill prey by constriction or by biting and swallowing Characteristics and Natural History of Reptilian Orders

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66. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-66 Venomous Snakes Venomous Snakes Family Viperidae Family Viperidae Includes New World and Old World vipers with and without pits Includes New World and Old World vipers with and without pits Family Elapidae Family Elapidae Includes cobras, mambas, coral snakes, and kraits Includes cobras, mambas, coral snakes, and kraits Family Hydrophiidae Family Hydrophiidae Includes the specialized sea snakes Includes the specialized sea snakes Family Colubridae Family Colubridae Most are non-venomous Most are non-venomous Several, including the African boomslang and African twig snake, are rear-fanged and bite can be fatal to humans Several, including the African boomslang and African twig snake, are rear-fanged and bite can be fatal to humans Characteristics and Natural History of Reptilian Orders

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68. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-68

69. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-69 Snakebite and Toxicity Snakebite and Toxicity Saliva of harmless snakes contains limited toxins Saliva of harmless snakes contains limited toxins Provided a basis for natural selection of venom Provided a basis for natural selection of venom Most snake venoms are a complex combination of venom types Most snake venoms are a complex combination of venom types Neurotoxins act on the nervous system, causing blindness or inhibit respiration Neurotoxins act on the nervous system, causing blindness or inhibit respiration Hemorrhagin type venoms break down blood vessels Hemorrhagin type venoms break down blood vessels Blood leaks into tissue spaces Blood leaks into tissue spaces Toxicity is measured by the median lethal dose in laboratory animals, called the LD50 Toxicity is measured by the median lethal dose in laboratory animals, called the LD50 Sea snakes and the Australian tiger snake have the most deadly venom per unit volume Sea snakes and the Australian tiger snake have the most deadly venom per unit volume Characteristics and Natural History of Reptilian Orders

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71. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-71 Large venomous snakes deliver more venom Large venomous snakes deliver more venom In India and Burma, dense populations and poor footwear contribute to 200,000 bites per year In India and Burma, dense populations and poor footwear contribute to 200,000 bites per year Characteristics and Natural History of Reptilian Orders

72. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-72 World total for deaths from snakebite is about 50,000 to 60,000 each year World total for deaths from snakebite is about 50,000 to 60,000 each year Most deaths occur in India, Pakistan, Myanmar, and nearby countries where poorly shod people frequently come into contact with venomous snakes or do not get immediate medical attention once bitten Most deaths occur in India, Pakistan, Myanmar, and nearby countries where poorly shod people frequently come into contact with venomous snakes or do not get immediate medical attention once bitten Less than 20% of all snakes are venomous, although venomous species outnumber nonvenomous species by 4 to 1 in Australia Less than 20% of all snakes are venomous, although venomous species outnumber nonvenomous species by 4 to 1 in Australia Characteristics and Natural History of Reptilian Orders

73. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-73 Reproduction Reproduction Most are oviparous and lay shelled eggs Most are oviparous and lay shelled eggs Others, including pit vipers, are ovoviviparous Others, including pit vipers, are ovoviviparous A few snakes are viviparous, having a primitive placenta to exchange nutrients with the young A few snakes are viviparous, having a primitive placenta to exchange nutrients with the young Female snakes can store sperm and lay several clutches of fertile eggs long after a single mating Female snakes can store sperm and lay several clutches of fertile eggs long after a single mating Characteristics and Natural History of Reptilian Orders

74. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-74 Order Sphenodonta: The Tuatara Only 2 living species in New Zealand represent this ancient lineage Only 2 living species in New Zealand represent this ancient lineage Sphenodontids radiated modestly in the early Mesozoic but then declined Sphenodontids radiated modestly in the early Mesozoic but then declined Once widespread across New Zealand, the 2 species are now restricted to small islands Once widespread across New Zealand, the 2 species are now restricted to small islands Loss of the tuatara populations caused by human introduction of nonnative species which preyed upon the tuatara Loss of the tuatara populations caused by human introduction of nonnative species which preyed upon the tuatara Tuatara are vulnerable because they have slow growth and reproductive rates Tuatara are vulnerable because they have slow growth and reproductive rates Characteristics and Natural History of Reptilian Orders

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76. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-76 Lizard-like and live in burrows often shared with petrels Lizard-like and live in burrows often shared with petrels Slow growing and may live to 77 years of age Slow growing and may live to 77 years of age Skull nearly identical to diapsid skulls of 200 million years ago Skull nearly identical to diapsid skulls of 200 million years ago Well-developed median parietal eye buried beneath skin Well-developed median parietal eye buried beneath skin Sphenodon represents one of the slowest rates of evolution known among vertebrates Sphenodon represents one of the slowest rates of evolution known among vertebrates Characteristics and Natural History of Reptilian Orders

77. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-77 Order Crocodilia: Crocodiles and Alligators Modern crocodilians are the only surviving reptiles of the archosaurian lineage Modern crocodilians are the only surviving reptiles of the archosaurian lineage Clade gave rise to the Mesozoic radiation of dinosaurs and to birds Clade gave rise to the Mesozoic radiation of dinosaurs and to birds Modern crocodilians differ little from primitive crocodilians of the early Mesozoic Modern crocodilians differ little from primitive crocodilians of the early Mesozoic There are 3 families of modern crocodilians There are 3 families of modern crocodilians Alligators and caimans are found primarily in the New World and have a broader snout Alligators and caimans are found primarily in the New World and have a broader snout Crocodiles are widely distributed Crocodiles are widely distributed One species of gavial occurs in India and Burma and has a very narrow snout One species of gavial occurs in India and Burma and has a very narrow snout Characteristics and Natural History of Reptilian Orders

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79. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26-79 All have long, well-reinforced skull and jaw musculature for a powerful bite All have long, well-reinforced skull and jaw musculature for a powerful bite Theocodont dentition Theocodont dentition Teeth are set in sockets Teeth are set in sockets Have a complete secondary palate, a feature only shared with mammals Have a complete secondary palate, a feature only shared with mammals Four-chambered heart Four-chambered heart Alligators and crocodiles are oviparous Alligators and crocodiles are oviparous Usually 20–50 eggs are laid in mass of vegetation Usually 20–50 eggs are laid in mass of vegetation Unguarded nests are easily discovered and raided by predators Unguarded nests are easily discovered and raided by predators High nest temperatures produce males High nest temperatures produce males Low temperatures produce females Low temperatures produce females Can result in females outnumbering males 5 to 1 Can result in females outnumbering males 5 to 1 Characteristics and Natural History of Reptilian Orders