Animal Evolution Notes

Ancestral Protist to Metazoa

  • Metazoa: Includes animals without a spine (invertebrates).
  • Symmetry Types:
    • Radial symmetry (e.g., Radiata).
    • Bilateral symmetry (e.g., Bilateria).
  • Germ Layers:
    • Diploblastic: Two cell layers.
    • Triploblastic: Three embryonic layers (includes a mesoderm).

Key Invertebrate Groups

  • Porifera (Sponges): Sessile, no true tissues, collared cells (choanocytes).
  • **Ctenophora:
  • Cnidaria: Diploblastic, two forms (sessile polyp and motile medusa), single opening to gastrovascular cavity.
  • **Acoela
  • **Platyhelminthes
  • **Rotifera

Deuterostomia Characteristics

  • Deuterostome Development forming radial symmetry at maturity, bilateral symmetry at the larval stage.
  • Examples: Hemichordata, Echinodermata, Chordata.
  • Echinodermata: Ambulacral system for feeding, respiration, locomotion, and excretion.

Chordate Characteristics

  • Five Key Traits (at some stage of development):
    • Notochord.
    • Dorsal, hollow nerve cord.
    • Pharyngeal slits or clefts.
    • Muscular, post-anal tail.
    • Muscle attached to notochord for locomotion

Key Evolutionary Milestones

  • Eumetazoa: Appeared ~770 million years ago.
  • Bilateral Symmetry: Evolved ~680 million years ago.
  • Triploblastic Layer: Evolved ~670 million years ago.

Protostomia Division

  • Lophotrochozoa: Have either a lophophore (ciliated tentacles) or a trochophore larval stage.
  • Ecdysozoa: Produce an exoskeleton and undergo ecdysis (molting).
    • Includes Nematoda (worms) and Arthropoda (rigid exoskeleton with appendages).

Chordate Evolution

  • Notochord: Common ancestor of chordates.
  • Vertebrates: Evolved through paedomorphosis.
  • Cyclostomes: Jawless vertebrates (e.g., hagfishes, lampreys) with a circular mouth.

Gnathostomes

  • Vertebrates with Jaws: Jaws evolved from gill arches.
  • Duplication of Hox genes

Osteichthyans

  • Bony skeleton
  • Actinopterygii: Ray-finned fishes.
  • Lobe-fins/Sarcopterygians:
    • Actinistia
    • Dipnoi: Functional lungs.

Tetrapods

  • Limbs with Digits

Amniotes

  • Amniotic egg
  • Reptilia (turtles, snakes, crocodiles, birds)
  • Mammalia (milk)

Tetrapod Adaptations for Land

  • Support against gravity
  • Air Breathing
  • Sensory organs adapted to the air
  • Resistance to drying

Amniotic Egg

  • Extraembryonic Membranes:
    • Chorion: Gas exchange.
    • Amnion: Protects against impacts and drying.
    • Allantois: Waste storage.
    • Yolk sac: Nutrient store.

Amphibians

  • Double life: Aquatic larval stage, terrestrial adult stage.
  • Three groups: Urodela (tail), Anura (no tail), Apoda (no limbs).

Reptiles

  • Scales containing keratin.
  • Internal fertilization.
  • Ectothermy (except birds).

Birds (Derived Reptiles)

  • Adaptations for Flight: No bladder, single ovary, small gonads, no teeth, light skull.
  • Wings and feathers

Mammals

  • Fur and milk production.
  • Endothermy.
  • Kidneys for water conservation.
  • Large brain.
  • Differentiated teeth.

Mammalian Groups

  • Monotremes: Lay eggs.
  • Marsupials: Premature birth, complete development in ventral pouch.
  • Eutherians: Placental mammals with complete embryonic development in the uterus.

Primates

  • Traits: Opposable thumbs and toes, nails, large brain, parental care, binocular vision.

Human Evolution

  • Upright, bipedal primates.
  • Reduced jaw bones.
  • Homo neanderthalensis is the closest to homo sapiens
  • Homo sapiens: Only surviving species of hominid tree.