Lepidosauria and Squamata Overview

Lepidosauria

  • Lepidosauria clade includes tuataras, all lizards, and snakes.
  • Tuataras: Single species in its own order, Rhynchocephalia.
  • Squamata: Contains over 10,000 species including lizards and snakes.

Phylogeny

  • Synapsida, Lepidosauria, Squamata, Amniota, Mammals.
  • Diapsida includes turtles, crocodilians, and birds.
  • Key physical features:
    • Skull with specific openings (lateral temporal openings in diapsids).
    • Presence of keratin in scales of lepidosaurs.
  • Evolutionary History:
    • Early lizards first appear in the Triassic period.
    • Snakes evolved from lizards at the end of the Cretaceous period.
    • Diversification during the Triassic or possibly earlier.

Shared Features

  • Skin Shedding:
    • Lepidosaurs shed their skin in one piece.
    • Scales are keratinized and overlapping (a unique characteristic enabling simultaneous shedding).
  • Autotomy:
    • Ability to regenerate tails; an anti-predation mechanism.
    • Features fracture planes where tails can be detached.

Tuataras

  • Derived from Māori "Tuatara" meaning “peaks on the back.”
  • First appeared in the Triassic.
  • Primarily found in New Zealand (now reduced populations on offshore islands).
  • Unique dentition: jaws are adept for specific feeding techniques (scissoring)
  • The Parietal Eye: well-defined in juveniles, functioning as a third eye.

Reproduction of Tuataras

  • Maturity at 10-20 years.
  • Oviparous, breeding every four years with temperature-dependent sex determination.
  • Lifespan can exceed 100 years in captivity.

Squamata

  • Includes all lizards and snakes; about 6500 lizard species and 3600 snake species.
  • Display determinant growth patterns different from turtles and crocodilians.
  • Kinetic Jaws: Higher flexibility due to secondary articulating points allowing the ingestion of large prey.

Reproductive Patterns in Squamata

  • Most squamates are oviparous; some exhibit viviparity or ovoviviparity.
  • Typically, no parental care except for some species that protect nests.
  • Display hemipenes for internal fertilization.

Squamata Phylogeny

  • Comprises many families:
    • 42 families of lizards.
    • 24 families of snakes.
  • Groupings have evolved with Gekkota (geckos), Scincomorpha (skinks), Dibamidae (blind skinks), and Lacertoidea.
  • Toxicofera: Subclade that includes all venomous lizards.

Feeding and Anatomy of Snakes

  • Snakes are limbless, with paired organs on one side and repetitive body segmentation.
  • Unique jaw articulation allows drastic feeding adaptations:
    • Can constrict powerful prey or use venom.
    • Their skulls are highly mobile to accommodate large prey ingestion.

Manitoba Diversity

  • Limited due to climate; features five snake species:
    • Western Hognose, Smooth Green, Northern Red-bellied, Plains Garter, Eastern/Redd-sided Garter.
  • Single skink species: Northern Prairie Skink.
  • Narcisse Snake Dens: Largest gathering of snakes, where red-sided garter snakes gather for hibernation.

Conclusion

  • Lepidosauria encompasses diverse reptiles with unique anatomical and ecological adaptations, from the basal tuatara to the highly specialized squamates like snakes and lizards. Their evolutionary history reflects significant adaptations that enhance survival across varied environments.