Exam 2 Lecture 3

Introduction to Fish Phylogeny

• Fish phylogeny represents vertebrate phylogeny.

• Understanding fish is crucial to understanding vertebrate relationships.

• Major groups derived from common ancestors over millions of years.

Diversity Over Time

• Proportional diversification depicted in a radiating tree graph.

• Current day represented by the outer circle of the tree, going back 570 million years.

• Common ancestor to all vertebrates noted around 570 million years ago, emphasizing fish as basal vertebrates.

Major Vertebrate Groups

Base Groups

• Common vertebrate ancestor leads to:

  • Modern Amphibians

  • Amniotes

• Everything that is not an amphibian falls under fish classifications.

Key Diversification Events

• Significant diversification occurred within the last 600 million years, as complex life appeared around 600 million years ago.

Diversity of Modern Fishes

Dominance of Teleosts

• The most diverse group of modern fishes are Teleosts, characterized by:

  • High taxonomic diversity (thicker branches in phylogenetic trees).

  • More species than any other vertebrate group combined.

Definitions and Types

• Actinopterygii: Ray-finned bony fishes, the majority of modern fishes.

• Teleostomes: Vertebrates possessing endochondral bone, includes teleosts.

Phylogenetic Connections

Sister Groups to Teleosts

• Ancient sister groups include:

  • Sturgeons

  • Gars

• Known as "living fossils", representing ancient lineages.

Additional Major Groups

• Chondrichthyes: Includes sharks, rays, and skates.

• Agnatha: Jawless fish, consists of lampreys and hagfish.

  • Concept of "worm" not scientifically defined, as the term varies among species.

Extinct Fish Groups

Placoderms

• Extinct jawed fish featuring bony plates, earlier dominant marine predators.

• Thought to be large but more refined evidence suggests they were not as massive as previously believed.

Elasmobranchs

• Sharks and rays noted for their diverse forms within

• Closely related to chimeras (ratfish and elephantfish).

Additional Fish Characteristics

Adaptations in Breathing Structures

• Gas Bladder vs. Lung:

  • A gas bladder allows buoyancy control in modern bony fishes.

  • In some ancient fish groups, it is connected to the digestive tract, functioning as a lung.

The Role of a Reit Mirabolae

• Capillary beds aiding in gas exchange within gas bladders.

• Similar functional roles observed in various vertebrate structures (lungs, kidneys).

Summary of Key Groups and Features

• Actinopterygii: Most modern ray-finned fishes, crucial to fish biology

• Sarcopterygi: Includes lobe-finned fishes which lead to tetrapods.

• Major phyla and subphyla defined within vertebrate classifications important for understanding evolution.

Conclusion

• This lecture provides a structured overview of fish phylogeny, major groups within the vertebrate family tree, and the significance of adaptations for survival and diversification within aquatic environments.