Chordates Notes

Chapter 6: Chordates

  • License: This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Slides adapted from the Textbook Chapter 9 (p779).

Lecture Objectives

  • Describe the characteristics shared by all chordates.
  • Discuss the different morphological features used to classify different groups within Chordata.
  • Describe the main characteristics shared by all Vertebrates.
  • Distinguish Gnathostomes from other Vertebrates.
  • List the differences between Bony and Cartilaginous fish, including examples.
  • Describe the different groups within Tetrapods and their characteristics.
  • Describe the main groups within Amphibia and their characteristics.
  • Understand the main characteristics of Reptiles and their current clades.
  • Describe the main characteristics of Mammals and their classifications.
  • Understand the main characteristics within Primates and the groups classified under this clade.

Introduction to Chordates

  • Three Domains of Life:
    • Bacteria
    • Archaea
    • Eukarya (includes Animalia, Plants, Fungi, and other groups like Entamoebae).

Characteristics of Chordates

Five Key Characteristics Shared by All Chordates:
  1. Dorsal Hollow Nerve Chord:
    • A hollow tube derived from ectoderm.
  2. Post-anal Tail:
    • Extends beyond the anus; used in motility.
  3. Pharyngeal Slits:
    • Openings of the pharynx extending to the outside environment, used in respiration and feeding in different species.
  4. Notochord:
    • A flexible rod-shaped structure located between the digestive tube and the nerve chord; provides support.
  5. Endostyle/Thyroid Gland:
    • A structure involved in feeding and hormone regulation; can develop into thyroid gland.
Nonvertebrate Chordates
1. Cephalochordates (Lancelets)
  • Notochord extends into the head; lacks a well-defined brain and has a simple nervous system.
  • Typically found buried in sand at the bottom of tropical seas.
2. Urochordates (Tunicates)
  • Covered by a tunic, a cellulose-like material.
  • Adults lack a notochord, dorsal hollow nerve chord, or post-anal tail.

Vertebrates Categorization

Vertebrate Characteristics
  • Vertebrates are characterized by the development of a dorsal vertebral column that replaces the notochord during early development, providing structural support.
  • Individual units make up this column, known as vertebrae.
Types of Vertebrates:
A. Jawless Fish (Petromyzontida - Lampreys)
  • Characterized by a rasping tongue and toothed mouth. Many lampreys are parasitic, attaching to larger fish.
B. Jawed Fishes (Gnathostomes)
  • Distinguished by the presence of jaws and paired fins.
    • Cartilaginous Fishes (Chondrichthyes): Consisting of sharks, rays; have a skeleton made of cartilage, sexually reproduce with primarily ovoviviparous reproduction.
    • Bony Fishes (Osteichthyes): Characterized by an internal skeleton of calcified bones, overlapping scales, and a swim bladder for buoyancy. Divided into ray-finned fishes and lobe-finned fishes.
    • Lobe-finned Fishes: Possess thick, supportive bones allowing some to walk on land.

Amphibians

  • Split into two main groups: Amphibians and Amniotes.
  • Characteristics include moist, permeable skin; requirement for living near water; and many undergo complete metamorphosis.
  • Life Cycle: Begins with eggs in water, progresses through stages (tadpoles) to adult forms.
Groups of Amphibians include:
  • Salamanders (Urodela)
  • Frogs (Anura)
  • Caecilians (Apoda)

Amniotes

General Characteristics:
  • Distinguished from amphibians by the development of an amniotic egg which provides aquatic environments for embryos,
  • Adaptations include waterproof skin and rib ventilation for lungs.
Reptiles:
  • Characteristics:
    • Lay eggs with shells on land.
    • Reproduce sexually with internal fertilization.
    • Have scaly skin containing keratin to reduce water loss.
    • Ectothermic (depend on environmental heat).
Major Groups include:
  • Squamates: Lizards and snakes (carnivorous).
  • Testudines: Turtles with bony or cartilaginous shells.
  • Theropods: Bird ancestors, characterized by specialized hip and wrist bone structures.
Mammals

Key Features:

  • Sweat glands, mammary glands, hair, and a four-chambered heart.
  • Three groups:
    • Monotremes: Egg-laying mammals.
    • Marsupials: Young develop in pouches.
    • Eutherians: Placental mammals with variations across species.
Primates:
  • Evolved from small, arboreal insectivorous eutherians.
  • Characteristics include rotating shoulder joints, opposable thumbs, stereoscopic vision, and larger brains.

Classification of Primates

Two Groups:
  • Prosimians
  • Anthropoids: Includes monkeys, apes, and humans.
Apes:
  • Generally larger, no tails, more intelligent with comparatively larger brains.
  • Divided into lesser apes and great apes (Family: Hominidae).
  • Great apes: Genera include Pan (chimpanzees, bonobos), Gorilla (gorillas), Pongo (orangutans), and Homo (humans).