C9 Vertebrates

Vertebrates (Kingdom Animalia)

Chapter Outline

  • Overview of Chapter 8 on Vertebrates.

Learning Objectives

  • By the end of this chapter, students should be able to:

    • Describe general characteristics of chordates.

    • Discuss characteristics of invertebrate chordates:

      • Subphylum Urochordata

      • Subphylum Cephalochordata

    • Describe vertebrates’ general characteristics.

    • Discuss respective groups in subphylum Vertebrata:

      • Fishes

      • Amphibia

      • Reptilia (Understanding amniotes characteristics)

      • Aves

      • Mammals

    • Explain primate, hominoid, and hominid evolution.

Phylum Chordata

  • Phylum Chordata is divided into three subphyla:

    1. Subphylum Cephalochordata (invertebrate chordates)

    2. Subphylum Urochordata (invertebrate chordates)

    3. Subphylum Vertebrata (vertebrates)

  • Majority of species are vertebrates (with a backbone), while invertebrate chordates make up a minority.

Characteristics

  • Chordates are:

    • Deuterostome coelomates with bilateral symmetry.

    • Typically possess an endoskeleton and a closed circulatory system.

    • Have a segmented body, though segmentation may not be obvious. For instance, muscles and nerves in vertebrates are segmented.

General Characteristics of Chordates

  • Four primary traits that characterize chordates:

    1. Notochord:

      • A long flexible rod of mesodermal tissue found in all chordates; in vertebrates, it is replaced by the vertebrae of the backbone.

    2. Dorsal Nerve Cord:

      • A hollow nerve cord positioned above the notochord that develops into the brain in vertebrates.

    3. Pharyngeal Slits:

      • Present at some stage and facilitate gas exchange in aquatic vertebrates as well as form jaws in other vertebrates.

    4. Postanal Tail:

      • A tail that exists after the anus, providing locomotion in aquatic species.

Additional Details

  • The notochord supports the body and evolves into bony vertebrae in vertebrates.

  • Pharynx functions as a muscular tube: gill slits serve in feeding and respiration.

Subphylum Cephalochordata (Lancelets)

  • Lancelets (amphioxus) are small, fish-like animals with:

    • Tapered bodies, resembling simpler fish.

    • Lack defined head, jaws, fins{sirip}, and hearts.

Feeding & Movement

  • Filter feeders, burrowing into sand and filtering food from water.

  • Simple brains controlled reflex responses.

  • Segmented muscle arrangement on both sides of the notochord.

  • Closed circulatory system; respiration through diffusion across the body wall.

Characteristics

  • Exhibit all four vertebrate characteristics throughout life:

    • Notochord, dorsal hollow nerve cord, segmented muscles, pharyngeal slits.

Subphylum Urochordata (Tunicates)

  • Marine organisms covered in gelatinous tunics.

Life Stages

  • Larval Stage:

    • Resembles a tadpole, possesses notochord, nerve cord, and tail; motile.

  • Adult Stage:

    • Becomes a sessile filter feeder, losing notochord and tail.

    • Expands pharynx for enhanced filter feeding and respiration.

Adaptations

  • Have protective tunics with incurrent and excurrent siphons for water flow.

  • Known as sea squirts due to expulsion of water when disturbed.

Evolution of Craniates

  • Craniates are chordates with a brain encased in a cranium (cartilage or bone).

  • Jawless fish, such as ostracoderms, represent early craniates.

Fossil Evidence

  • Primitive craniate: Haikouella.

  • Jawless armored vertebrates: Pterapsis

  • Living examples: lampreys and hagfishes, characterized by ovoid shape and lack of jaws.

Evolutionary Trends of Vertebrates

  1. Replacement of notochord with vertebrae forming backbone.

  2. Development of jaws, evolving from gill support structures.

  3. Evolution of limbs from fish fins.

  4. Increased reliance on lungs and advanced circulatory systems.

Evolution of Jawed Fishes (Gnathostomes)

  • Jaws evolved from gill-supporting skeletal rods; adaptation led to successful aquatic life.

  • Various adaptations in jawed fish allowed for improved survival rates.

  • These fishes display structural features for movement, reproduction, and feeding.

Rise of Amphibians (Tetrapods)

  • Amphibians are the first successful land vertebrates, characterized by:

    • Adaptations for life on land, including limbs for mobility.

    • Biophysical challenges from aquatic environments, demanding evolution in respiratory systems.

Adaptations

  • Amphibians possess bony endoskeletons and typically four limbs.

  • Migrated to terrestrial habitats established better oxygen intake through lung adaptations.

Mammalian Evolution

  • Mammals exhibit a range of traits including:

    • Mammary glands for nursing.

    • Enlarged brains for increased cognitive functions.

    • Hair as an insulative layer.

Lineages of Mammals

  • Major groups:

    • Monotremes: lay eggs (e.g., platypus, spiny anteater).

    • Marsupials: pouched mammals; e.g., kangaroos and Tasmanian devils.

    • Eutherians: placental mammals with developed placentas.

Primate Evolution

  • Key adaptations in primate evolution include:

    1. Enhanced vision in depth perception.

    2. Bipedalism: adaptation for upright walking.

    3. Dexterous grip with opposable thumbs for tool-making.

    4. Evolution of teeth linked to diet variations.

Social Evolution

  • Increased complexity in behavior and social structures, leading to cultural development in humans.

Conclusion of Vertebrate Evolution

  • Evolution of mammals continues to demonstrate significant adaptations for survival in diverse environments. Adaptations in traits optimize their functionality and ecological interactions.