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ABCS 406: VERTEBRATE BIOLOGY - REPTILES

Prof. D. K. Attuquayefio, DABCS, Legon

INTRODUCTION

  • Latin Origin:

    • “repto” = crawl/creep

  • Worldwide Species Diversity:

    • Total Number: Approximately 7,000 species.

    • Distribution: 6,000 species, making up 86% are lizards and snakes.

    • Other Groups: Includes chelonians (tortoises and turtles), crocodiles, tuataras, amphisbaenids.

  • Adaptations:

    • Reptiles are highly adapted to terrestrial life, being the first true terrestrial vertebrates.

GENERAL CHARACTERISTICS

  1. Reproductive System:

    • Internal Fertilization: Use of an intromittent organ (hemipenis in males, penis).

    • Development: Direct; eggs develop into adults without an aquatic larval stage, eliminating the need for water for reproduction.

    • Reproductive Strategies: Generally oviparous, but some species (e.g., certain snakes) are ovoviviparous.

  2. Physical Characteristics:

    • Skin: Dry, scaly skin to prevent desiccation and abrasion from movement.

    • Excretory System: Highly effective, featuring complex kidneys that excrete uric acid as a pasty crystal form with minimal water.

  3. Egg Structure:

    • Large, extensively yolked, shelled cleidoic eggs with embryonic membranes (amnion, chorion) providing necessary nutrients for embryos.

  4. Skeletal Features:

    • Well-ossified skeletons for efficient terrestrial movement.

  5. Respiratory System:

    • Efficient pulmonary (lung) respiration, except for Chelonia which utilizes cloacal respiration.

  6. Thermoregulation:

    • Ectothermic; behavioral thermoregulation is observed.

  7. Nervous System:

    • Complex cerebral cortex leading to more intricate behavior compared to amphibians.

  8. Cardiovascular System:

    • Generally three-chambered heart (two auricles and one ventricle); Crocodylia species have a four-chambered heart with complete separation.

EVOLUTION

  • Labyrinthodonts (Amphibia): Existed approximately 350 million years ago.

  • Seymouriamorps: Considered missing links between amphibians and reptiles.

  • Cotylosaurs (Primitive Reptiles): Emerged around 300 million years ago.

  • Major groups include:

    • Anapsida: Includes Chelonians (tortoises, turtles, terrapins).

    • Lepidosauria: Consists of Diapsids, including Squamata (lizards and snakes).

    • Archosauria: Encompasses thecodonts (early dinosaurs, crocodilians, and birds) and Theromorpha (mammal-like reptiles leading to Mammalia).

DIVERSITY

Class Reptilia

  • Subclass Anapsida:

    • Order: Chelonia (Tortoises, turtles, terrapins).

  • Subclass Lepidosauria:

    • Order: Rhynchocephalia (Tuataras).

    • Order: Squamata (Lizards, snakes).

    • Suborder: Lacertilia/Sauria (Lizards).

    • Suborder: Serpentes/Ophidia (Snakes).

    • Suborder: Amphisbaenia (Amphisbaenids).

  • Subclass Archosauria:

    • Order: Crocodilia (Crocodiles, alligators, caimans).

Families of Chelonia and Characteristics

  1. Family: Pelomedusidae (Marshy area family with hinged plastron allowing for head withdrawal).

    • Example:

      • Pelomedusa subrufa (Marsh terrapin).

    • Sexual Dimorphism: Males have thicker, longer tails than females, who exhibit broader carapaces.

    • Example: Pelusios gabonensis (African forest turtle) - endemic to Africa.

  2. Family: Dermochelidae (Leatherback turtles).

    • Conservation Status: Endangered marine turtles without a bony shell.

    • Example: Dermochelys coriacea (Leatherback sea turtle) - largest of all turtles.

  3. Family: Testudinidae (Land Chelonians/Tortoises).

    • Conservation Status: Most species listed as 'Vulnerable' by IUCN.

    • Examples:

      • Kinixys belliana (Bell's hinged tortoise).

      • Geochelone elephantopus (Galapagos giant tortoise) - largest tortoise.

  4. Family: Chelonidae (Marine Turtles).

    • Examples:

      • Chelonia mydas (Green sea turtle) - herbivorous, 'Endangered' by IUCN.

      • Eretmochelys imbricata (Hawksbill sea turtle) - 'Critically Endangered'.

  5. Family: Trionychidae (Soft-shelled river turtles).

    • Characteristics: Leathery carapace; female usually larger than male; primarily carnivorous and need to be submerged for swallowing.

    • Example: Trionyx triunguis (Soft-shelled river turtle).

  6. Family: Sphenodontidae (Tuataras).

    • Characteristics: Lizard-like reptiles lacking copulatory organs and external ears.

    • Example: Sphenodon punctatus (Tuataras).

  7. Family: Agamidae (Agama/Rainbow Lizards).

    • Characteristics: Diurnal, insectivorous lizards with sexual dimorphism; males exhibit brighter colors.

  8. Family: Gekkonidae (Geckos).

    • Characteristics: Nocturnal, insectivorous, equipped with adhesive feet; exhibit autotomy.

  9. Family: Scincidae (Skinks/Snake-lizards).

    • Characteristics: Long bodies, reduced hind limbs; some are limbless.

  10. Family: Chamaeleonidae (Chameleons).

    • Characteristics: Specialized for arboreal living; features include monocular vision and camouflage abilities.

  11. Family: Varanidae (Monitor Lizards).

    • Characteristics: Largest lizards; carnivorous diet.

  12. Family: Helodermatidae (Exotic venomous lizards).

    • Example: Heloderma suspectum (Gila monster).

  13. Family: Gerrhosauridae (Plated Lizards).

    • Example: Gerrhosaurus major (Plated lizard).

  14. Family: Anguidae (Leg-less lizards, Slow Worms).

    • Example: Anguis fragilis (Slow worm).

  15. Family: Iguanidae (New World Lizards).

    • Distinct sexual dimorphism with attractive male features.

  16. Suborder: Amphisbaenia (Amphisbaenids).

    • Primitive leg-less burrowing reptiles.

Families of Serpentes and Characteristics

  1. Family: Leptotyphlopidae (Worm/Thread Snakes).

    • Characteristics: Subterranean and non-venomous; called “two-headed” due to similar structure of head and tail.

  2. Family: Typhlopidae (Blind/Glass Snakes).

    • Example: Typhlops punctatus (Spotted blind snake).

  3. Family: Boidae (Boas/Pythons).

    • Reproductive Modes: Boas are ovoviviparous; pythons are oviparous.

    • Example: Eunectes murinus (Anaconda) - world's largest snake.

  4. Family: Colubridae (Colubrids).

    • Characteristics: Largest snake family; non-venomous species that kill by constriction.

    • Examples:

      • Lamprophis fuliginosus(Black house snake).

      • Philothamnus irregularis (Green tree snake).

  5. Subfamily: Colubrinae (Non-venomous Colubrids).

  6. Subfamily: Dasypeltinae (Egg-eating Snakes).

    • Example: Dasypeltis scabra (Egg-eating snake).

  7. Subfamily: Boiginae (Venomous Colubrids).

  8. Family: Elapidae (Cobras and Mambas).

    • Characteristics: Venomous snakes with front fangs.

    • Examples:

      • Naja nigricollis (Spitting cobra).

      • Dendroaspis viridis (Green Mamba).

  9. Family: Hydrophidae (Sea Snakes).

    • Adaptations for aquatic life.

    • Example: Hydrophis sp. (Sea snake).

  10. Family: Viperidae (Vipers, Adders, Rattlesnakes).

    • Characteristics: Venomous snakes with hinged front fangs.

    • Example: Crotalus adamanteus (Eastern Diamondback Rattlesnake).

GENERAL BIOLOGY

FEEDING ADAPTATIONS

  • Diet: Majority are carnivorous.

  • Tongue Variations:

    • Squamata: Protrusible.

    • Crocodilia/Chelonia: Non-protusible; longest found in chameleons.

    • Snakes and Monitor Lizards: Bifid tongues.

  • Dentition Types:

    • Homodont dentition (teeth absent in Chelonia).

    • Acrodont (non-socketted, top jaw): Squamata.

    • Pleurodont (non-socketted, side of jaw): Squamata.

    • Thecodont (socketted): Crocodilia.

  • Jaw Mechanics: Large jaw muscles to crush prey, with variations in feeding habits between juveniles (smaller prey) and adults (larger prey).

SNAKE FEEDING ADAPTATIONS

  • Teeth Structure: Recurved for swallowing; modification for fangs seen across families.

  • Venom Types:

    • Neurotoxic (nerve-acting): Found in Elapidae.

    • Haemotoxic (blood-acting): Found in Viperidae.

  • Venom Delivery: Venom gland connected to fangs via a venom duct; paired quadrate bones allow significant jaw opening for prey capture.

OSMOREGULATION

  • Excretory Products: Uric acid, characterized as non-toxic with low solubility; excretion conserves water.

  • Kidneys: Metanephric structure efficient in water conservation.

  • Urinary Bladder:

    • Absent in crocodiles and snakes; present as bilobed in lizards and chelonians.

GAS EXCHANGE

  • Mechanism: Dependent primarily on lungs; more efficient than amphibians.

  • Chelonians: Use cloacal and pharyngeal respiration due to inefficient rib movement related to their shells.

SKELETAL AND MUSCULAR SYSTEM

  • Skull Structure: Light and kinetic in snakes; robust in crocodiles.

  • Limbs: Vestige in boas, pythons; modified into flippers in turtles; lizards typically are pentadactyl.

  • Vertebral Count: Snakes typically have 130-500 vertebrae, with associated ribs.

    • Autotomy prevalent in lizards, allowing self-defense mechanisms.

SKIN

  • Skin Function: Dry and scaly for abrasion protection and water retention; chelonians possess a protective carapace.

  • Epidermal Shedding: Periodic ecdysis; snakes shed whole, lizards shed in pieces.

NERVOUS AND SENSORY SYSTEMS

  • Brain Structure: Similar to amphibians; larger cerebrum enables complex behaviors.

  • Vision: Generally well-developed, but snakes (except tree snakes) have poor eyesight.

  • Hearing: Lack tympanic membrane; snakes detect vibrations via the inner ear linked to the quadrate bone.

  • Chemoreception: Well-developed Jacobson’s organ for detecting chemical cues.

  • Thermovision: Presence of heat-sensitive pits for hunting warm-blooded prey.

LOCOMOTION

  • Types in Snakes:

    • Serpentine: Typical S-shaped movement for speed.

    • Concertina: For navigating tight spaces.

    • Rectilinear: Slow, straight-line movement, primarily seen in heavy-bodied species.

    • Sidewinding: Adapts to loose, hot subsurface environments, using minimal body contact with the ground.

THERMOREGULATION

  • Ectothermic: Suffer behavioral thermoregulation; optimal survival temperatures vary with habitat.

  • Preferred Temperatures:

    • Snakes: 26 °C

    • Lizards: 33 °C

    • Alligators: 34 °C

    • Turtles: 28 °C

  • Methods: Shuttling, burrowing, hibernation, aestivation, color change, and panting for heat regulation.

REPRODUCTIVE BIOLOGY OF REPTILES

  • Evolutionary Changes:

    • Direct development eliminating aquatic larval stages; cleidoic eggs provide nutrients; internal fertilization using an intromittent organ.

SEXUAL DIMORPHISM

  • Differences: Male reptiles differ in shape, size, and coloration; these can be permanent or seasonal.

    • Example: Male lizards larger with bright colors, female snakes possess longer tails.

SEX RECOGNITION

  • Attractive Features: Males have distinct traits like enlarged dewlaps and may use head bobbing to signal females.

  • Recognition Methods: Females are passive; males utilize behaviors, scents, and tactile cues for recognition.

COURTSHIP

  • Territorial Behavior: Well-defined male territories often overlap with females; combat dances among some species for mating rights.

  • Courtship Actions: Includes nudging, grabbing, and distinct mating postures, especially prominent in squamates.

COPULATION AND FERTILIZATION

  • Internal Fertilization: All reptiles have this reproductive mechanism, utilizing distinct mating practices among various families to ensure embryo protection.

EGG-LAYING AND HATCHING

  • Process: Fertilization leads to eggs laid in varying forms of parental care; young snakes are born ready to hunt.

LONGEVITY

  • Comparative Longevity:

    • Chelonians ≥ Tuataras ≥ Crocodiles ≥ Snakes ≥ Lizards

  • Examples:

    • Galapagos Giant Tortoise: 152 years

    • Tuatara: 60-100 years

    • Alligator: 56 years

    • Black Cobra: 29 years

    • Anaconda: 29 years

    • Gila Monster: 20 years

End of Notes