Campbell Biology - Invertebrates and Vertebrates Study Notes

Introduction to Invertebrates

  • Authors: Nicole Tunbridge and Kathleen Fitzpatrick

  • Textbook Reference: Campbell Biology, 12th Edition.

Phylum Chordata

  • Characteristics:

    • Dorsal hollow nerve chord

    • Notochord

    • Pharyngeal slits

    • Muscular post-anal tail

Phylogeny of the Chordates

  • Ancestral Chordates Discussion

    • Cephalochordates: Lancelets

    • Urochordata: Tunicates

    • Myxini: Hagfishes

Lancelets (Cephalochordates)

  • Type: Invertebrate chordates

  • Adult Characteristics:

    • Notochord persists throughout adulthood, serving as a proto-skeleton.

    • Pharyngeal slits are adapted for filter feeding.

    • Adults burrow into the ocean floor, exposing tentacles for feeding.

Tunicates (Urochordata)

  • Common Name: Sea squirts

  • Characteristics:

    • Tunicate larvae exhibit all four core characteristics of chordates.

    • Larvae do not feed and quickly anchor themselves using a sucker.

    • Adults filter feed by drawing water into their pharynx.

Chordata: Subphylum Vertebrata

  • Major Groups:

    • Agnathostomes through primates.

Evolution of Vertebrates

  • Key Evolutionary Features:

    • Skull and backbone composed of vertebrae.

    • Includes hagfishes and lampreys as jawless vertebrates.

  • Evolutionary Milestones:

    • Jaws and mineralized skeletons appear in early vertebrates.

    • Progressive complexity from ray-finned fishes to lobed-finned fishes.

Vertebrate Development

  • Development Process:

    • The vertebral column develops around and later absorbs the notochord.

    • The vertebral column surrounds the dorsal hollow nerve chord, providing protection.

  • Features of Vertebrates:

    • Well-developed head, characterized by cephalization.

    • Embryonic neural crest cells give rise to structures like melanocytes, cranial neurons, and teeth.

    • Possession of internal organs, heart, and a closed circulatory system.

    • Endoskeleton composed of cartilage or bone.

Living Vertebrates

  • Agnathostomes:

    • First vertebrates evolved lacked true jaws.

    • Hagfishes and lampreys: Only existing jawless vertebrates, possessing teeth made of keratin.

Evolution of Jaws

  • Developmental Origins:

    • Jaws likely evolved from the cartilaginous rods that held gill slits open.

    • True teeth (dentine) evolved from scales lining the mouth.

Placoderms (Extinct Group)

  • Characteristics:

    • First vertebrates with jaws and bony plates instead of true teeth.

    • Often grew quite large, reaching lengths of 30 feet.

Chondrichthyes (Sharks, Rays, Skates)

  • Evolutionary Timeline: Evolved approximately 400 million years ago.

  • Characteristics:

    • Cartilaginous skeleton reinforced with calcium carbonate in outer layers.

    • Teeth are not anchored to bone or cartilage, indicating independent evolution.

    • Example: Ancient sharks, such as Megalodon, existed 2.6 million years ago.

Buoyancy in Chondrichthyes

  • Utilizes squalene oils in the liver and heterocercal tail for buoyancy, preventing sinking.

  • Unique spiral valve intestine slows food movement and increases digestion efficiency.

Osteichthyes (Bony Fishes)

  • Characteristics:

    • Strong, heavy internal skeleton; increased buoyancy needs addressed with swim bladder, which can inflate or deflate using gases from the blood.

    • Operculum helps fan water over gills, allowing for improved gas exchange.

Ray-Finned vs. Lobe-Finned Fishes

  • Actinopterygii (Ray-Finned Fishes):

    • Fins supported by parallel bony rays attached to a shoulder girdle without musculature.

  • Sarcopterygii (Lobe-Finned Fishes):

    • Fleshy muscular lobes supported by bones; ancestral forelimbs are significant in the evolution of tetrapods.

Terrestrial Challenges and Adaptations

  • Challenges:

    • Supporting body weight, increased oxygen needs, prevention of desiccation, and functional gas exchange organs on land.

Early Amphibians

  • Example: Icthyostega, likely spent considerable time in water (flipper-like hindlimbs, scales, gills).

  • Fossil Age: Approximately 370 million years old.

Modern Amphibians

  • Key Features:

    • Tetrapod limbs, lung tissue supplemented by skin gas exchange.

    • Partial heart separation; pulmonary veins aid in oxygenating blood.

    • Most species require water for gelatinous eggs.

Reptile Adaptations for Water Independence

  • Amniotic Egg:

    • Watertight structure with a shell; chorion allows gas exchange while retaining moisture.

    • Amnion encloses the embryo in fluid; yolk sac provides nutrients.

Reptiles: Skin and Breathing

  • Dry Skin Adaptations:

    • Scales composed of keratin protect against water loss.

  • Breathing Mechanism:

    • Rib cage expansion increases air intake compared to amphibian throat breathing; internal fertilization.

Classification of Living Reptiles

  • Major Orders and Examples:

    • Squamata, suborder Sauria: Lizards (3800 species)

    • Squamata, suborder Serpentes: Snakes (3000 species)

    • Rhynchocephalia: Tuataras (1 species)

    • Chelonia: Turtles, tortoises (250 species)

    • Crocodylia: Alligators, crocodiles (25 species)

Birds: Evolution and Characteristics

  • Origin: 150 million years ago with Archaeopteryx fossils.

  • Adaptations for Flight:

    • Feathers (modified scales) for insulation and flight.

    • Hollow, reinforced bones and a highly efficient respiratory system.

Bird Respiratory System

  • Mechanism:

    • Parabronchi and air sacs facilitate unidirectional air flow, improving oxygen exchange and minimizing stale air mixing.

Evolution of Mammals

  • Timeframe: Appeared approximately 220 million years ago.

  • Mammal Features:

    • Possess hair for temperature regulation, sensory functions, and defense.

    • Mammary glands for feeding young.

    • Endothermy, four-chambered heart, and a diaphragm for enhanced breathing.

Types of Mammals

  • Monotremes: Egg-laying mammals with a cloaca; possess fur and mammary glands.

  • Marsupials: Birth to a fetus which continues development in a pouch; most species found in Australia, facing extinction.

  • Placental Mammals: Majority of mammals, including humans; utilize placentas for nutrient and gas exchange.

Diversity in Mammals

  • Example Orders:

    • Proboscidea (Elephants)

    • Rodentia (Beavers, mice)

    • Carnivora (Bears, cats)

    • Primates (Humans, lemurs)

    • Chiroptera (Bats)

Re-colonization of Aquatic Environments by Mammals

  • Examples: Manatees and dugongs evolved from ungulate-like ancestors; orcas belong to Order Cetacea, descending from ancestors similar to hippopotamuses.

Primate Evolution

  • Key Characteristics:

    • Grasping hands and feet, flattened nails, and binocular vision for depth perception.

  • Common Ancestors: Likely resembled a small, nocturnal rodent-like animal similar to a tree shrew.

  • Earliest primate fossils date back to about 50-55 million years ago.

Divergence of Nonhuman Apes

  • Timeline: Approximately 25-30 million years ago.

  • Features: Larger brains, loss of tail, complex social structures.

Hominins: Human Evolution Line

  • Shared Traits with Humans:

    • Reduced canine teeth, flat faces, increasing bipedalism, foramen magnum positioned beneath the skull.

Key Hominid Species

  • Homo habilis:

    • First human species appearing 2.5-2 million years ago; brain size of 660 cc; found alongside stone tools.

  • Homo erectus:

    • Existed between 1.8 million and 30,000 years ago; robust build; first to migrate outside of Africa; coexisted with Homo habilis.

  • Diversified Species:

    • Many species arose from Homo erectus, such as Homo floresiensis (a dwarf species).

Neanderthals and Modern Humans

  • Coexistence: Neanderthals lived alongside modern humans; interbreeding occurred.

  • Characteristics: Stout body form, large brain; may have been outcompeted by the more energy-efficient Homo sapiens, which arose approximately 200,000 years ago.