Vertebrate Zoology: Early Terrestrial Tetrapods (Stem Amohibians and Rwptiles

Overview of Wildlife Resources and Transition to Modern Amphibians

• Wildlife Resources Classes
    - Offered in Fall
    - Plenty of slots available

Introduction to STEM Amphibians

• Continuation on discussion about STEM (Stegocephali) amphibians

• Transitioning into modern amphibians

Early STEM Tetrapods

• Review of early STEM tetrapods

• Focus on aquatic to terrestrial transition in vertebrates

• Two significant fish species discussed:
    - Erypodistines
      - Serves as starting point for limb evolution
    - Panorhichnids
      - Exhibits further changes in skeletal structure

Discovery of Tiktaalik

• Fossil Evidence
    - Long gap in fossil record from fish to early tetrapods
    - In 2004, dig on Ellesmere Island, Canada by researchers from University of Chicago and Field Museum
    - Discovery of Tiktaalik as a transitional fossil

Significance of Tiktaalik

• Known as a “fishapod”
    - Combines features of fish and tetrapods
    - Skull resembles tetrapod structure while body remains fish-like

• Characteristics of Tiktaalik:
    - Flat skull (indicative of tetrapods)
    - Presence of forelimbs with rudimentary digits
    - Well-preserved fossil evidence (three individuals found)

Evolutionary Traits of Tiktaalik

• Analysis of anatomical features:
    - Humerus bone
      - Structure similar to tetrapods
      - Aligns it phylogenetically closer to tetrapods than fish
    - Flattened skull structure (compared to Eusenopteron and Pantyrrhachis)

• Movement capabilities:
    - Swimming and mobility in shallows, utilizing limb structures

Subsequent Discoveries

• Introduction of Elpistostege watsonii
    - Possesses mammal-like digits
    - Forelimbs indicative of early tetrapods

• Fossil Evidence indicates that distinctions between fish and tetrapod lineage continued to evolve

Transition to True Tetrapods

• Focus on early true stem tetrapods

• Example Species:
    - Acanthostega
      - Primarily aquatic with unelongated limbs
      - Dorsoventrally flattened tail
    - Ichthyostega
      - More terrestrial, capable of movement both on land and in water
      - Notable morphological differences:
        - Robust skeleton, developed limbs, broad skull for feeding

Fossil Timeline

• Important timeline: 385–365 million years ago for early tetrapod fossils
    - Evidence of tetrapod gait from 397 million years ago (trackway evidence)
    - Lack of transitional fossils between Devonian and Carboniferous periods

Evolutionary Divergence

• Splitting of amphibians and reptiles post-Devonian

• Characteristics distinguishing stem amphibians from stem amniotes:
    - Skull shape, digit counts, tail shape, reproduction methods

• Importance of fossil morphology analysis in understanding evolutionary transitions

Modern Amphibians Overview

• Class Amphibia:
    - Includes modern amphibians and their ancestors

• Major groups:
    - Urodela (salamanders and newts) - 420 species
    - Anura (frogs and toads) - Over 3,800 species
    - Gymnophiona (caecilians) - Poorly understood, subterranean

Characteristics of Modern Amphibians

• Defined traits include skin features:
    - Lack of scales or armor

• Ecological adaptations:
    - Habitat diversity ranging from aquatic to terrestrial environments
    - Examples of behavioral adaptations for reproduction (e.g., Darwin's frog)

Summary and Study Points

• Key fossil evidence bridges the evolutionary gap between aquatic fishes and terrestrial tetrapods

• Importance of understanding morphology and ecological adaptations in modern amphibians

• Identification of evolutionary traits from stem amphibians to modern groupings \n

Final Discussion Points

• Implications of skin adaptations in amphibians

• Need for further research and exploration of amphibian diversity in unique environments

• Importance of fossil record in tracing the evolution of early tetrapods to modern amphibians.