exam 2 lecture 4

Chapter 1: Introduction to Sarcopterygii

• Definitions and Key Terms

  • Sarcopterygii: Derived group of lobe-finned fishes; name refers to their fleshy, lobed fins.

  • Actinopterygii: The ray-finned fishes, contrasting with the fleshy fins of sarcopterygians.

  • Paraphyly: Sarcopterygii is described as a paraphyletic group with multiple branches and no single phylogenetic tree.

• Coelacanth

  • Key member of sarcopterygii discovered relatively recently; thought to be extinct.

  • Visual appearance similar to common osteichthyes, having typical fish characteristics but with distinctive fleshy lobed fins.

  • Significance: Acts as a "living fossil," providing insight into the evolutionary transition to terrestrial life.

• Evolutionary Importance

  • Coelacanths exhibit significant evolutionary traits not found in actinopterygians, such as a fully developed pectoral girdle.

  • They serve as an important reference for understanding the evolution of land vertebrates.

• Lungfishes

  • Another extant group within sarcopterygii.

  • Possess lungs and other morphological traits resembling early tetrapods.

  • Adaptations allow them to survive in seasonal waters, possibly providing insights into the evolution of amphibians.

Chapter 2: Finned Fish and Clades

• Cladistics vs. Phylogenetics

  • Importance of defining clades: Sarcopterygii forms a clade with tetrapods, illustrating their evolutionary relationship.

  • Debate on whether to consider tetrapods as separate from sarcopterygii or included within them in discussions of fish paraphyly.

• Sarcopterygii with Tetrapods

  • The clade encompasses all lobe-finned fishes and their descendants, primarily tetrapods.

  • Distinction between historical evolutionary branches and extant species is emphasized.

Chapter 3: Median Fin Changes

• Fin Morphology

  • Transitioning from fish to tetrapods involves significant anatomical changes, especially regarding median fins.

  • The reduction of dorsal and median fins is associated with terrestrial adaptation.

Chapter 4: Hollow Nerve Cord and Skin Development

• Notochord and Neural Development

  • Overview of vertebrate body plan emphasizes the notochord and hollow nerve cord structure.

  • Somites: Clusters of mesodermal cells developing into various body structures like muscles and dermis.

• Skin Structure

  • Divided into epidermis (ectoderm) and dermis (mesoderm); key for sensory perception, protection, and bodily functions.

  • Importance of layers: dermis contains blood vessels and nerve endings; epidermis provides protection.

Chapter 5: Skin as an Organ System

• Functions of Skin (Integumentary System)

  • Protection: Physical barrier against injury and infection.

  • Osmoregulation: Maintains hydration and electrolyte balance; crucial in burn injuries.

  • Thermoregulation: Key to regulating body temperature via blood flow adjustments in the skin.

• Immunity and Sensation

  • The skin serves as the first line of defense against pathogens; disruptions to the skin can lead to infections.

Chapter 6: Further Protection Mechanisms

• Protection from Environmental Stressors

  • Thermal regulation benefits both cold and warm-blooded vertebrates through adaptations in skin.

  • Role in camouflage and radiation defense underscores evolutionary significance.

Chapter 7: Conclusion

• Evolutionary Context

  • The transition from aquatic to terrestrial life reflected in the morphological adaptations of both skin and anatomical features.

  • The significance of understanding vertebrate evolution roots in the changes to these foundational systems as they adapted to life on land.