VE Lecture 4

SOEE1120 Vertebrate Evolution Notes

Lecture Overview

  • Title: Origin of the Tetrapods; Terrestrialisation; Amphibian Evolution
  • Relevant Reading: Benton Chapter 4

The Devonian World

  • Timeframe: Early Devonian (~390 million years ago)
  • Geography:
    • Ancient and modern landmasses
    • Major features include subduction zones and sea floor spreading ridges
    • Notable regions: Siberia, North China, South China, Kazakstania, Bali, Euramerica, GONDWANA, etc.

Terrestrial Life in the Devonian

  • Ecosystems:
    • Emergence of small terrestrial plants in late Silurian to early Devonian
    • Development of terrestrial invertebrate communities noted by early Devonian
    • Formation of proper forests by late Devonian

Fossil Record of Fish-Tetrapod Transition

  • Timeline of key fossils:
    • Middle to Late Devonian (Eifelian to Famennian)
    • Important genera include: Tiktaalik, Acanthostega, Ichthyostega, and many others
    • Classification of transition fossils as either Tetrapoda or Elpistostegalia

Challenges of Life on Land

Skeletal Support
  • Issue: Need for spinal support due to increased gravity on land.
Locomotion

  • Mode 1: Transition of Fins to Legs

    • Fossils showing gradual modification from fish-like structures to limbs.
    • Example species: Eusthenopteron (A), Early Tetrapod (B) noting pentadactyl limbs (five fingers/toes).

  • Mode 2: Limb Girdle Modifications

    • Changes in shoulder girdle (separation from the skull) and pelvic girdle (attachment of ilium to vertebral column).
    • Example species: Osteolepiform fish (A), Basal tetrapod (B)
Feeding and Breathing
  • Changes in Anatomy:
    • Reduction in hinge joints, single point of jaw hinge
    • Evolution from gills to lungs (ancestral fish already had lungs)
Reproduction and Water Balance
  • Reproduction Challenges:
    • Need for amphibians to return to water or develop desiccation-resistant eggs for amniotes.
    • Water balance considerations led to adaptations in skin permeability.

Key Fossils of Later Tetrapods

  • Genus Information:
    • Tiktaalik: late Devonian, features include robust shoulder, enlarged pelvis.
    • Acanthostega & Ichthyostega: late Devonian, known for pentadactyl limbs (often higher number of digits than expected).

The Late Carboniferous World

  • Period: Late Carboniferous (~306 million years ago)
  • Environment:
    • Coal swamps along the Pangaean equator with diverse flora:
    • Notable plants include giant club mosses, lycopods, and horsetails.
    • Habitat supporting diverse invertebrates, e.g., giant dragonflies.

Nýřany Lake, Czech Republic

  • Fauna:
    • Early tetrapods: embolomeres, temnospondyls, etc.
    • Palaeoenvironment: Enclosed lake surrounded by coal swamps

Evolution of Modern Amphibians

  • Lineages:
    • Frog and toads (Anura) with earliest fossils from early Triassic
    • Salamanders and newts (Urodela) dating back to mid Triassic
  • Morphological Adaptations:
    • Jumping adaptations in Anurans and body structure modulations seen in Urodela.

Next Lecture

  • Upcoming Topic: Evolution of the Amniotes: The story of eggs and skulls