MODERN REPTILES

Systematic Classification

• Clade Anapsida
    - Subclass Anapsida
    - Order Chelonia (Testudines, Testudinatata)

• Clade Diapsida
    - Subclass Archosauria
      - Order Crocodylia
    - Clade Aves (Birds, if applicable)
    - Subclass Lepidosauria
      - Order Rhynchocephalia
      - Order Squamata
        - Suborder Amphmibaenia
        - Suborder Lacertilia
        - Suborder Serpentes

SNAKES

Overview of Suborder Serpentes

• Species Diversity
    - 3400+ species of snakes
    - 438+ genera
    - 18-23 families

• Geographic Distribution
    - Cosmopolitan distribution, except for sub-arctic regions
    - Lizards inhabit all places snakes do not

Key Characteristics of Serpentes

• Morphological Traits
    - Lack of limbs
    - Absence of pectoral girdle
    - No external ear openings
    - Existence of a modified Eustachian tube
    - Lack of eyelids
    - Tail autotomy (in most species)
    - Presence of a transparent eye scale (spectacle)

• Skeletal Anatomy
    - Most vertebrae consist of trunk and caudal sections
    - Approximately 120 precaudal vertebrae, total vertebrae can exceed 500+
    - Most snake species possess the largest number of ribs among vertebrates

Skull Adaptations

• Cranial Features
    - Features cranial kinesis
    - Reduced number of skull bones
    - Double articulation of the suspensorium
    - Streamlined bone structure allowing more mobility
    - Lack of mandibular symphysis
    - Jaws capable of independent movement—upper and lower jaws can articulate separately

• Dental Structure
    - Variations in tooth morphology observed among families:
      - Caudally curved teeth
      - Multiple rows of teeth
      - Protection by integument

• Specialized Teeth
    - Types found:
      - Aglyphous (without fangs)
      - Opisthoglyphous (rear fangs with grooves)
      - Proteroglyphous (front fangs, typically fixed)
      - Solenoglyphous (folding front fangs)

Predatory Strategies

• Methods of Feeding
    - Predatory strategies include ambush (sit and wait) and continuous foraging
    - Specialized muscle structure for swallowing prey whole, with capacity to ingest objects up to three times head diameter

• Venoms
    - Modified salivary secretions served for toxicity
    - Classification of venoms:
      - Neurotoxic (affects the nervous system)
      - Hemolytic (breaks down tissues)
    - Venoms produced by various glands:
      - Duvernoy’s gland in colubrids, neurotoxins in elapids, hemotoxins in vipers

Ecology and Habitat

• Diversity
    - Habitat range includes arboreal environments, terrestrial regions, and aquatic ecosystems

• Coloration and Patterning
    - Warning coloration seen in species such as coral snakes; cryptic patterns for camouflage in others like the Gaboon viper

Reproductive Biology

• Fertilization Types
    - Internal fertilization through hemipenes
    - Oviparous (egg-laying) and viviparous (live-birthing) reproductive strategies
    - One species, Brahminy Blind Snake, known for true parthenogenesis

• Courtship Behaviors
    - Unique behaviors observed, including male-to-male combat and twisting around females during mating

Taxonomic Families

• Family Viperidae (Pit vipers, rattlesnakes, aspids)
    - 305+ species distributed among several subfamilies
    - Notable specificity in morphology, including reduced premaxilla and unique fang structure

• Family Elapidae
    - 62 genera featuring highly venomous species such as cobras and mambas
    - Presence of the left carotid artery and reduced left lung

• Family Colubridae
    - 290 genera exhibiting a diverse range of morphologies and ecological adaptations

Notable Species Explored

• Longest Snake
    - Reticulated Python (Python reticulatus): Can grow up to 10 m (33 ft), recognized as the heaviest snake at 350 kg (770 lb)

• Smallest Snake
    - Ringneck Snake (Diadophis punctatus): Reaches lengths of approximately 30 cm (12 in)

Notable Facts

• Evidence of Gigantism
    - Titanoboa cerrejonensis: Fossils found in Northern Colombia - reported length of 30 meters

• Unique Predatory Strategies
    - Some snakes employ sit-and-wait strategies, while others actively hunt