Herpetology Lecture Notes: Early Tetrapod Diversity and the Invasion of Land

Herpetology: Introduction

• Herpetology is the study of amphibians and reptiles.
• Course: ENS-1402, taught by Prof. Wolfgang Wüster, School of Natural and Environmental Sciences.

About the Instructor

• Name: Wolfgang Wüster
• Research Interests:
  • Evolution of snake venom
  • Biodiversity and taxonomy of venomous snakes (evolutionary relationships, discovery of new species)
  • Conservation
  • Genomics
  • Biogeography

Challenging Perceptions

• False statement: This is the Age of Mammals; reptiles and amphibians are insignificant leftovers from the Age of Reptiles (ended ~65 Mya with dinosaur extinction).

Reality Check: Biodiversity

• More than half of all ~38,865 land vertebrate species are reptiles or amphibians.
• This highlights the significant diversity of these groups compared to mammals and birds.

Reality Check: Size Extremes

• The largest partly terrestrial predator is a reptile: Saltwater crocodile (Crocodylus porosus).
  • Max length: ~6 meters
  • Max weight: ~1000 kg
• The smallest land vertebrate is an amphibian: Eleutherodactylus iberia – Cuban robber frog.
  • Max length: 10 mm

Significance of Studying Amphibians and Reptiles

• Key roles in understanding various biological fields:
  • Developmental biology: Frog development.
  • Ecology: Diurnal activity patterns, niche segregation, and ecology of lizards.
  • Experimental evolution: Responses of island lizards to novel selection pressures (e.g., introduced predators, natural disasters).
  • Physiology: Extreme remodeling of internal organs after feeding in snakes; thermoregulation and temperature tolerance in lizards.
  • Medicine: Snake venoms as key research tools; drugs from frog and snake toxins.

Lecture Outline

• Lecture 1: Splendors of the Past: Early land vertebrate diversity and the invasion of the Land.
• Lecture 2: Splendors of the Past: The Age of Giants. Diversity of fossil amniotes [interrupted by 2 lectures by James Hicks].
• Lecture 3: Diversity of present-day Amphibians.
• Lecture 4: Diversity of present-day non-avian Reptiles.

Conquest of the Land: Experimental Evolution in Action

• Key innovations and occupation of new habitats provide freedom for evolutionary experimentation.
• Invasion of Land was a major step in vertebrate evolution.
  • Large numbers of basal lineages.
  • Convergent morphologies with extant vertebrates.
  • Extreme morphologies unknown in today’s vertebrates.
  • Unusual evolutionary trends.
  • Mass extinctions as triggers of radiations.

Phylogenetic Systematics

• Illustrates the evolutionary relationships between various fish and tetrapod groups, highlighting the position of humans, frogs, and other vertebrates within the broader tree of life.

The Path onto Land – New Discoveries

• New fossil discoveries (Greenland, Canadian Arctic, E. Europe, Australia) are crucial.
  • Multiple new transitional fossils.
  • Better quality fossils (e.g., 3D preservation).
  • Re-evaluation of long-known taxa, e.g., Ichthyostega.
• New technologies are being utilized.
  • CT scans of bones in rock.
  • 3D reconstructions.
  • Functional analysis.
• Many knowledge gaps remain, emphasizing the ongoing nature of research in this field.

Fish-Tetrapod Transition

• Key transitional fossils and their approximate ages:
  • Eusthenopteron: 385 MYA
  • Panderichthys: 382 MYA
  • Tiktaalik: 375 MYA
  • Acanthostega: 365 MYA
  • Ichthyostega: 362 MYA

Functional Studies

• Eusthenopteron, a lobe-finned fish, has long been used as an example of an early tetrapod predecessor, informing our understanding of the evolution of terrestriality.

Tiktaalik roseae

• A lobe-finned fish intermediate between typical sarcopterygians and basal tetrapods.
  • Mid to Late Devonian; 375 million years old.
  • Shows a mixture of typical lobe-finned “fish” and tetrapod features such as a flat head, neck, and eyes on top.
  • Expanded ribs

Tetrapod Origins: Limbs before Terrestriality

• Acanthostega:
  • Early aquatic tetrapod - 365 Mya
  • Possessed a tetrapod limb skeleton and bones supporting gills.

Ichthyostega

• The