This document provides an overview of amphibian and reptilian anatomy and physiology. It summarizes their taxonomy, ectothermic metabolism, integumentary systems, vision, cardiovascular and respiratory systems, hearing, and other key anatomical features. Unique characteristics are described for reptiles and amphibians in each system compared to mammals. The focus is on comparing and contrasting their anatomical adaptations.

1. Amphibian and Reptilian Anatomy and Physiology

2. Learning Objectives List the taxonomic orders in the classes Reptilia and Amphibia. Define ectothermic and explain how ectothermic animals regulate their body temperatures. List the unique features of the reptilian and amphibian integumentary systems. Describe the process of ecdysis. List the unique features of reptilian and amphibian vision and hearing. List the components of the reptilian and amphibian heart and describe the flow of blood through the heart. Describe the unique features of the reptilian and amphibian respiratory and gastrointestinal systems. Describe the structure of the kidneys of reptiles and amphibians. Describe the factors that determine the sex of offspring of reptiles and amphibians. List the unique features of the musculoskeletal systems of reptiles and amphibians.

3. Taxonomy Class Reptilia - four orders: Crocodylia (alligators and crocodiles) Squamata (snakes and lizards) Chelonian (turtles and tortoises) Rhyncocephalia (tuataras)

4. Taxonomy Class Amphibia - three orders: Gymnophiona (caecilians) Anura (frogs and toads) Caudata (salamanders and newts)

5. Metabolism Ectothermic animals are unable to generate body heat internally. Body temperature depends on environmental temperature Some reptiles can raise body temperatures via metabolic processes (e.g., muscular contractions) Herptiles - maintain body temperatures via behavioral thermoregulation (e.g., postural changes)

6. Ectothermy Related to energy conservation Animal regulates temperature depending on metabolic needs Allows many herptiles to survive on very small amounts of food Depends on access to temperatures within the preferred optimal temperature zone (POTZ) POTZ: range of temperatures in which the animal can perform all necessary metabolic functions

7. Reptile Integument Keratinized skin Alpha keratin - soft, flexible, found in interscalar skin Beta keratin - rigid, found in scales Limited subcutaneous space

8. Reptile Integument Dermis - dense connective tissue Blood and lymph vessels, nerves, and chromatophores (pigment-containing cells) Chromatophores allow some lizards to change skin color and pattern Osteoderms: bony plates within dermis of some lizards and crocodilians

9. Reptile Integument Scales - formed by epidermal folds in most reptiles Vary in size and shape Brille (spectacle): modified scales that may cover eyes Other epidermal structures may be present Crests, tubercles, spines, and dewlaps

10. Reptile Integument Scale and scute nomenclature - aids in species identification and medical recording

11. Ecdysis Shedding of the skin Occurs with growth and in response to skin injury Process is controlled by thyroid gland Shed in pieces or in one large piece Shed skin: exuvia

12. Ecdysis Cells replicate new epidermis Enzyme-containing lymph secreted between old and new epidermal layers Skin color dulls; spectacle opacifies Lymph - resorbed prior to ecdysis Mechanical rubbing on objects

13. Amphibian Integument Epidermis - single or few layers of keratinized cells Aquatic amphibians - no keratinized cells Extremely permeable Absorb water directly from environment “ Drink patches”: areas of increased permeability on ventral surfaces Dermis - chromatophores and glands Glands produce secretions which help protect the amphibian’s skin

14. Amphibian Integument Toxic secretions - produced by some glands within dermis and epidermis Defense mechanisms Dermis: little subcutaneous space in salamanders and caecilians Anurans: looser attachments of dermis (more subcutaneous space) Amphibians regularly shed outer layers of epidermis

15. Vision Reptiles – iris made up of skeletal muscle under voluntary control Pupillary light reflex: consensual reflexes usually not seen Lower lid usually more mobile than upper

16. Vision Some species of lizards have thin, transparent lower lids Allows for a degree of vision even when lids are closed Cartilagenous pads (tarsal pads): found in lids of some reptiles Nictitans: well-developed, mobile in many reptiles

17. Vision Snakes, some lizards - no true eyelids Clear, fused scale (spectacle) Tear film - between cornea and spectacle in subspectacular space Tears drain into mouth through nasolacrimal duct system

18. Most reptiles - poorly developed extraocular muscles Exception - chameleons; eyes move freely and independently of one another Chelonians - no nasolacrimal ducts; tears spill over the lid margin Vision

19. Vision Lacrimal and harderian glands present in most reptiles and amphibians Produce secretions that combine to form the tear film Eyelids absent in some aquatic species Caecilians - eyes covered with skin Amphibian eyes - often protrude ventrally into the oral cavity when animal swallowing

20. Vision Ossicles: scleral bones present in most reptiles (except snakes and crocodilians) Lens: more fluid in reptiles than mammals (more rigid in snakes) Accommodation Chelonians - lens is squeezed through the pupil Snakes - lens moves back and forth due to pressure changes within the aqueous and vitreous humors

21. Vision Reptiles - avascular retinas Nutrition and waste removal via choroidal vessels in vitreous Conus papillaris: in lizards, extends into vitreous from optic disc provides nutrition and waste removal Crocodilians have a tapetum Parietal eye - found in some reptiles Rudimentary retina and cornea, no iris, lids, or musculature Exact function unknown May play a role in light-cycle-mediated hormone function

22. Cardiovascular System Location of the heart varies Chelonians - on midline just caudal to thoracic girdle, ventral to the lungs Most lizards - within thoracic girdle Crocodilians and some lizards - farther back in the coelomic cavity Snakes - usually at junction of the first and second third of the body length Fairly mobile within the coelomic cavity

23. Heart Two atria One ventricle

24. Heart Ventricle Regions Cavum venosum: paired aortic arches, lead to systemic circulation Cavum arteriosum: receives blood from pulmonary veins and directs oxygenated blood to cavum venosum Cavum pulmonale: receives blood from right atrium and directs flow into pulmonary circulation

25. Heart Pressure differences of outflow tracts and muscular ridge that partially separates cavum venosum and cavum pulmonale maintain separation of oxygenated and deoxygenated blood

26. Heart Rate Depends on species, size, temperature, activity level, and metabolic function Heart rate = 33.4 × (Weight in kg -0.25 ) Lizards - vasovagal reflex induces drop in heart rate, blood pressure, and a catatonic state Triggered by applying gentle pressure to both eyeballs through closed lids Lizard recovers with cessation of pressure or mild stimulation

27. Blood Cells Reptilian red blood cells: oval and nucleated RBC life span between 600 and 800 days Immature erythrocytes occasionally seen, especially in juveniles and during ecdysis

28. Blood Cells Heterophils: round with eosinophilic rod-shaped granules and round to oval nuclei Analogous to mammalian neutrophils without peroxidase and acid phosphatase Reptiles produce caseous pus instead of liquid material Eosinophils: similar appearance to heterophils but granules are round Basophils: small round cells with deeply basophilic cytoplasmic granules that may obscure the nucleus

29. Blood Cells Lymphocytes : vary in size; usually round cells with large nuclei, large nuclear-to-cytoplasm ratio, and no cytoplasmic granules Monocytes: oval or lobed nuclei, blue-grey cytoplasm, may contain small vacuoles or very fine granules Some reptile monocytes have small azurophilic granules (azurophils) Thrombocytes: small, oval, nucleated cells; colorless cytoplasm may contain small granules

30. Respiratory System Reptiles capable of surviving long periods without breathing Because of large pulmonary volume, reptiles have efficient anaerobic metabolism and cardiac shunting capabilities. Respiration driven by oxygen levels in blood

31. Respiratory System Glottis of most amphibians and reptiles: rostral portion of oral cavity Glottis very mobile in snakes; protrudes from mouth to allow respiration during ingestion of prey Paired arytenoid cartilages: border glottal opening; open during respiration

32. Respiratory System No vocal cords Only vocalizations possible are hissing, grunting, bellowing Frogs and toads - vocal sacs arise from trachea Glottal keel present in some species of snakes Increases volume of vocalizations

33. Pulmonary Tissues Honeycomb appearance Openings of honeycomb end at faveoli Fixed structures surrounded by capillaries Site of gas exchange Tracheal rings incomplete (except chelonians)

34. Reptile Lungs Unicameral lung Simple, saclike Cranial portion: site of gas exchange Caudal portion: avascular, comparable to avian air sac

35. Reptile Lungs Multicameral lung Many compartments Intrapulmonary bronchi

36. Reptile Lungs Paucicameral Lung Characteristics of both unicameral and multicameral lungs

37. Reptile Respiratory System No true diaphragms Action of intercostal muscles and parts of axial musculature used for respiration

38. Reptile Respiratory System Crocodilians - muscular septum caudal to lungs Cranial aspect of liver is attached to septum Caudal aspect of liver is attached to pubis by diaphramaticus muscle Lung inflation results from contraction of diaphramaticus moving the septum caudally

39. Amphibian Respiratory System Simple saclike lungs Some salamanders have no lungs Cutaneous respiration Pulmonary ventilation results from pumping of buccal cavity and pharynx Gas exchange can also occur across mucous membranes of buccal cavity, pharynx, and cloaca

40. Hearing Ears - both sides of head, usually caudal to eyes Tympanum - may lie in depression and/or be covered by folds of skin (some lizards and crocodilians) Columella - single bone in middle ear of reptiles Connects to tympanum and quadrate bone Transmits vibrations to oval window of cochlea Converted to nerve impulses and transmitted to the brain via the vestibulocochlear nerve

41. Hearing Semicircular canals control balance and equilibrium (reptiles) Snakes - no external ears; columella articulates with quadrate bone Allows snakes to be very sensitive to ground vibrations transmitted through the mandibles Snakes also able to hear aerial sounds Salamanders and caecilians - no tympanic membranes; columella may be degenerate

42. Feeding Strategies Carnivorous, omnivorous and herbivorous reptiles all exist Snakes, crocodilians, and adult amphibians are strict carnivores Some diets are very specialized

43. Oral Cavity Snakes and lizards: deeply forked tongues Function as particle delivery system for vomeronasal organ (accessory olfactory organ) Allow for detection of particle gradients

44. Oral Cavity Chameleons: specialized projectile tongues designed for capturing prey from long distances Sticky end which the prey items stick to Turtles and tortoises: typically thick, fleshy, relatively immobile tongues

45. Oral Cavity Crocodilians: immobile tongue attached to intermandibular space Muscular flaps from base of tongue and dorsal pharynx allow for opening of mouth while submerged without ingesting or inhaling water

46. Oral Cavity Tongue used to capture prey (most amphibians) Anurans, most terrestrial salamanders: caudodorsal aspect of tongue is flipped cranioventral to prehend food (lingual flipping)

47. Oral Cavity Numerous salivary glands Salivary secretions provide lubrication that aids in ingestion of large prey Also has enzymatic properties Venom glands (some snakes, lizards) - modified salivary gland

48. Dentition Turtles and tortoises No teeth Tomia (keratinized beaks) Other reptiles: 3 types of dentition

49. Types of Dentition Thecodont dentition: teeth arise from sockets in skull bones (crocodilians)

50. Pleurodont dentition: teeth attached to medial aspect of periosteum on mandibles and maxillae (snakes and iguanid lizards) Types of Dentition

51. Types of Dentition Acrodont dentition: teeth fused to biting edge of mandible and maxillae (some lizards)

52. Dentition Snakes have 6 rows of teeth: two mandibular, two maxillary, two on palantine/pterygoid bones Aglyphous snakes lack fangs

53. Dentition Venomous snakes - specialized dentition for venom delivery Proteroglyphous and opisthoglyphous - fangs are fixed upright Solenoglyphous - fangs are folded on roof of mouth when mouth is closed and are erect when snake bites

54. Dentition Venom-delivering teeth: hollow with an opening near end where venom expelled Fangs receive venom through a duct from venom gland at its base Contraction of muscles around venom gland forces venom out through the fang Snakes can control amount of venom delivered with each bite

55. Dentition Most amphibians have teeth Caecilians and salamanders - both maxillary and mandibular teeth Palatal teeth in some species Maxillary dentition present in some anuran species Odontoid process: cutting plates on rostral mandibles of some frogs

56. Esophagus Reptile - thin and distensible Unique morphology reflects type of prey Amphibian esophagus very short and wide, especially in anurans

57. Stomach Reptile - variable size and shape Snakes - highly distensible Crocodilians - thick muscle comparable to avian gizzard Amphibian - anurans capable of prolapsing stomach through the mouth; gastric prolapse is a terminal event in dying animals

58. Amphibian Intestinal Tract Indistinct regions Liver may contain melanomacrophages involved in immune function Pancreas - between stomach and proximal segments of intestine

59. Reptilian Intestinal Tract Varies according to diet Herbivores - longer intestinal tracts than carnivores Snakes - relatively straight intestinal tracts

60. Reptilian Intestinal Tract Colon - large and complex in herbivores Hindgut fermentation for digestion Cecae - site of hindgut fermentation in herbivorous lizards and chelonians Liver - usually large and bi-lobed

61. Cloaca Common outflow tract for GI and urogenital tracts (all reptiles and amphibians) Three chambers: coprodeum, urodeum and proctodeum

62. Reptile Kidney Usually oblong and smooth-surfaced Snakes - kidneys that are lobulated Ureters empty into dorsolateral aspects of the urodeum Some species do not have urinary bladders

63. Reptile Kidney No distinct renal pelvis Distal collecting tubules join into collecting ducts that merge to form the ureter No loop of Henle present Not able to concentrate urine as mammals do Water can be absorbed from urine through wall of the urinary bladder, rectum, or cloaca

64. Amphibian Kidney Nephrostomes - connect the coelomic cavity to the renal tubules; filter blood and coelomic fluid Kidneys usually lobulated and in caudodorsal coelomic cavity

65. Amphibian Kidney Some amphibians excrete ammonia as a nitrogenous waste product; others excrete urea, some excrete uric acid No ability to concentrate urine Urinary bladders and cloacal anatomy similar to reptiles

66. Reptile Reproductive System Males have internal testes located in dorsal coelomic cavity Ductus deferens leads from testes to dorsal wall of the urodeum Most also have a sexual portion to the kidney tubules Develops in response to high levels of circulating sex hormones Probably provide secretions that contribute to the seminal fluid

67. Reptile Reproductive System Copulatory organs vary in structure Crocodilians and chelonians - phallus of erectile tissue rising from floor of cloaca Snakes and lizards - paired hemipenes everted from the tail base through the vent

68. Reptile Reproductive System Females - paired ovaries in dorsal coelomic cavity Paired oviducts lead to cloaca and end at genital papillae in dorsal wall of the urodeum

69. Reptile Reproductive System Oviducts - 5 regions: infundibulum, magnum, isthmus, uterus, and vagina Albumin and shell - in oviparous species, added to ova in the oviduct prior to egg laying In viviparous species, fetuses are retained in uterine portion of oviduct

70. Reptile Reproductive Cycle Vitellogenesis - development and maturation of the follicles Triggered by environmental cues that stimulate release of FSH and estrogen Vitellogenin - lipid substance added to yolk within developing follicle Large amounts of calcium are also added In viviparous reptiles - some support of fetus Some lizards have true placentas

71. Reptile Reproductive Cycle Oviposition - many reptiles dig nests to lay eggs Without suitable nesting material, female may experience dystocia Chelonians and lizard species may excavate deep holes to deposit eggs

72. Reptile Reproductive Cycle After oviposition or parturition, reptiles not involved with care of eggs or offspring Exceptions - crocodilians protect their nests and young for a period of time following hatching Pythons and cobras - protect their nests until hatching

73. Egg Incubation Development and hatching requires proper temperature, humidity, and gas composition of nest Incubation time and temperature varies Reptile eggs should not be rotated during incubation

74. Sex Determination in Reptiles Determined by genotype or temperature at which eggs are incubated Sex chromosomes: Females are heterozygous (ZW) and males are homozygous (ZZ)

75. Sex Determination in Reptiles Some species do not have sex chromosomes Higher incubation temperatures produce males in crocodilians and lizards Opposite occurs in chelonians Temperature range within the nest allows for production of a mixed clutch of hatchlings

76. Secondary Sex Characteristics Snakes - no real sexual dimorphism In some species, pelvic spurs can be larger in males Pelvic spurs: remnants of pelvic limbs; provide tactile stimulation to females

77. Secondary Sex Characteristics Male chelonians may have concave plastron and more distally located vent Allows closer apposition of the cloacas when the male mounts the female Some lizards show obvious dimorphism Example: male Jackson’s chameleon has three well-developed horns on its face

78. Amphibian Reproduction Sexual dimorphism in some species Poison dart frog males have enlarged toe pads Large tympanic membranes in some male anurans Prominent cloacal glands in male salamanders

79. Amphibian Reproduction Paired gonads in dorsocaudal coelomic cavity Bidder’s organs - ovarian remnants near testes in male toads Most caecilians are viviparous Most anurans and salamanders are oviparous Amplexus - Male frogs and toads fertilize eggs as they are laid while grasping the female

80. Amphibian Reproduction Phallodeum - portion of cloaca in caecilians that is everted to deposit semen into female’s cloaca Spermatophores - packets of sperm deposited onto substrate by male salamanders Picked up by the female salamander’s cloaca Spermatotheca - pocket in cloaca of female salamanders where sperm can be stored

81. Amphibian Reproduction Eggs are usually deposited in or near water Some parental care of eggs and/or young in anurans and most salamanders Larval anurans (tadpoles) have completely aquatic lives prior to metamorphosis Tadpole metamorphosis - usually complete within 90 days Metamorphosis is stimulated by thyroid hormones

82. Endocrine System Single thyroid gland (except lizard) Crocodilians - bilobed thyroid has a thin isthmus between lobes Size of thyroid gland varies according to season and metabolic state Parathyroid glands and ultimobrachial bodies in cervical region

83. Endocrine System Adrenal glands - usually within the ligaments that suspend the gonads Produce epinephrine, norepinephrine, aldosterone, and corticosterone No distinct separation of adrenal cortex and medulla Exact location of endocrine organs in amphibians varies

84. Reptile Nervous System Three major divisions of reptilian brain Forebrain - olfactory lobes, cerebral hemispheres, diencephalon Midbrain - optic lobes, cerebral peduncles, nerve fibers connecting forebrain and hindbrain Hindbrain - cerebellum, medulla oblongata No surface gyri or sulci on the brain

85. Reptile Nervous System Brain meninges: pia-arachnoid layer and dura mater 12 cranial nerves Depend on spinal segmental reflexes and locomotor centers for control of movement

86. Amphibian Nervous System Brain - well developed for basic functions (sight, olfaction, and movement) 10 cranial nerves Spinal cord extends to the tip of the tail in amphibians and caecilians; ends in lumbar region in frogs and toads Animal dependent upon spinal segmental reflexes to control movement

87. Reptile Musculoskeletal System Types of skulls Anapsid: no temporal openings; chelonians Diapsid: temporal openings in the skull

88. Reptile Musculoskeletal System Snake skulls -extremely mobile Mandibular symphysis is connected by ligaments that allow jaws to move independently of each other

89. Snake Skulls Mandibular symphysis connected by ligaments allows jaws to move independently Quadrate bones - allow wider opening of mouth Moveable bones of maxillae and palate

90. Reptile Musculoskeletal System Spine - extremely flexible; presacral, sacral, and caudal-vertebral regions Single occipital condyle forms the articulation between skull and spine Well-developed ribs Exceptions: chelonians’ spine and ribs are fused to the bony shell

91. Amphibian Musculoskeletal System Skulls of anurans - broad and fenestrated Parts of the skull involved with olfaction and hearing are well developed Palate - poorly developed with reduced dentition Caecilians - compact, well-ossified skulls with well-developed dentition

92. Amphibian Musculoskeletal System Highly variable number of vertebrae Vertebrae - no distinctions of regions Salamanders and anurans also possess sacral vertebrae Anurans’ vertebrae are fused Urostyle - last caudal vertebra Caecilians lack a sternum Sternum is a small cartilaginous plate in salamanders

93. Axial Skeleton Tail autonomy - defensive mechanism Some lizards and salamanders Discarded tail usually continues to wiggle and distract predator The species capable of tail autonomy have “fracture planes” along which tails break Little to no blood loss Lost tail can regenerate; regenerated tail stiff and cartilaginous

94. Reptile Appendicular Skeleton Pectoral girdle - scapula and coracoid bone with muscular attachments to the body Pectoral limbs - humerus, radius, ulna, carpal bones, metacarpal bones, and phalanges Pelvic limb - femur, tibia, tarsal and metatarsal bones, and the phalanges Usually five digits on both front and rear feet

95. Reptile Appendicular Skeleton Spurs - vestigial pelvic limbs of some snake species Found on either side of the vent Used in courtship behavior Some lizards have very reduced limbs “ Legless lizards” retain vestigial thoracic and pelvic limb structures

96. Amphibian Appendicular Skeleton Pectoral girdle - primarily cartilaginous; consists of precoracoid, coracoid and scapula Exception - anurans’ pectoral girdle is completely ossified and consists of scapula, clavicle, and coracoid Pectoral limb - similar to reptile, except for radioulna (fused radius and ulna in anurans) Four toes usually present on the pectoral limbs Pelvic girdle - ilium, ischium and pubis

97. Amphibian Appendicular Skeleton Pelvic limb - elongated and well developed for swimming and jumping Elongated metatarsal bones in anurans Usually five toes are present

98. Muscular Structure In four-limbed amphibians and reptiles, musculature is somewhat analogous to that of mammals. Snakes: epaxial muscles and segmental muscles