Untitled

Tetrapods Overview

• Tetrapods evolved from lobe-finned fish during the Devonian (375 MYA).
• First amphibians like Acanthostega emerged in the late Devonian.

Key Groups of Tetrapods

• Amphibia: 3 orders: Urodela (newts & salamanders), Anura (frogs & toads), Apoda (caecilians).
• Amniotes: Diverged into Reptilia and Mammalia.

Characteristics of Amphibians

• Thin and permeable skin; require moist environments.
• External fertilization; eggs lack shells.
• Larvae typically aquatic with gills; adults are terrestrial and carnivorous.

Amniotic Egg

• Evolved in the Carboniferous; allows terrestrial life.
• Has four membranes: protection, gas exchange, nutrient storage.

Major Amniote Clades

• Reptilia: Includes Testudines (turtles), Crocodilia (crocodiles & alligators), Aves (birds).
• Mammalia: Diverse with hair, specialized teeth, and mammary glands.
• Earliest amniote: Hylonomus (312 MYA).

Evolutionary Milestones

• Transition from water to land involved adaptations like limbs with digits and lungs.
• Dinosaurs flourished in Triassic to Cretaceous periods, leading to the rise of mammals and birds in the Tertiary.

Unique Features of Major Groups

• Testudines: Unique shell morphology, ectothermic.
• Crocodilia: Semi-aquatic, minimal evolutionary change since the Triassic.
• Aves: Feathers, endothermic, specialized for flight.
• Sphenodontia: Retained ancestral features, primarily found in New Zealand.
• Squamata: Highly specialized with limb reduction in snakes.

Summary

• Amphibians require water for reproduction; amniotes are adapted to land.
• Continual revisions in taxonomic classifications across all groups.