Topics 29-35 Flashcards (Final Exam Themes)

Taxa of chordate clades

• Cephalochordata – Lancelets (e.g. Branchiostoma)

• Urochordata – Tunicates (e.g. sea squirts)

• Vertebrata – Vertebrates → Gnathostomes → Osteichthyans → Actinopterygii and Sarcopterygii

Evolution of tetrapods

• terrestrial adaptations (90–360 mya):

  • Waterproof skin, internal lungs, water-independent reproduction, strong skeletons.

• Transitional forms: had limbs + lungs/gills but were still aquatic:

  1. Weak limbs/ankles

  2. Short ribs = poor lung protection

  3. Fish-like tails damaged on land

Events in chordate evolution

• Cambrian: Early chordates and vertebrates.

• Ordovician: First jawless fish.

• Silurian: Jawed fish evolve.

• Devonian: Bony fish and first tetrapods.

• Carboniferous: Amphibians and reptiles evolve.

• Mesozoic: Reptiles dominate.

• Cenozoic: Mammals and birds diversify.

Amniotic eggs

• include extant reptiles, including birds, mammals, and many extinct groups, e.g. dinosaurs.

• Amniotic egg: key trait of amniotes.

• Four membranes: protection, nutrients, waste, gas exchange.

• Shell prevents desiccation.

• Adaptations: waterproof skin, internal fertilization, lung ventilation.

• Supports terrestrial life, independent of water

Diversification of amniotes

• Amniotes diversified into reptiles, birds, and mammals.

• Reptiles: Early amniotes, include turtles, lizards, snakes, and dinosaurs.

• Birds: Evolved from theropod dinosaurs, adapted for flight.

• Mammals: Evolved from synapsid reptiles, characterized by hair, mammary glands, and live birth.

• Adaptations across groups allow for survival in varied terrestrial environments.

Evolution of Birds

• Birds evolved from feathered theropods in the Jurassic (~165-150 mya).

• Archaeopteryx (oldest bird, ~150 mya) had both bird and dinosaur features: feathers, wings, teeth, bony tail, and wing claws.

• Theropod and bird similarities: hollow bones, egg-laying, brooding, feathers (homologous to scales), anatomical resemblances.

• Birds form a monophyletic lineage with rapid adaptive radiation after the evolution of wings and flight.

External vs internal fertilization

• External fertilization:

  • Occurs outside the body, common in aquatic environments (e.g., fish).

  • Large gamete numbers, but higher environmental risk.

• Internal fertilization:

  • Occurs inside the body, common in terrestrial animals (e.g., mammals).

  • More controlled, protective environment for embryo development.

Ectothermy vs. endothermy

• Ectothermy: Body temperature controlled by environment; energy-efficient.

• Endothermy: Body temperature controlled internally; energy-intensive but allows broader activity range.

Differentiating between mammals

• Monotremes: Egg-laying (platypus, echidna), no placenta.

• Marsupials: Live young, underdeveloped at birth, develop in a pouch (kangaroos, koalas).

• Eutherians: Fully developed live young, placenta for gestation (humans, elephants).

Characteristics of mammals

• Mammary glands: Produce milk.

• Hair: Keratin fibers.

• Middle ear bones: Detect higher frequencies.

• Endothermy: Regulate body temp.

• Jaw: Dentary and squamosal form the joint.

• Teeth: Specialized for diet.

• Larger brain: Complex behaviors.

• Other traits: Vertical limbs, diaphragm, internal fertilization

Trait development during hominin evolution

1. Early bipedalism: transition from arboreal to terrestrial locomotion.

2. Tool use.

3. Pelvic modification supported an upright posture and a more efficient bipedal gait.

4. Brain expansion (later): a gradual increase in cranial capacity led to enhanced cognitive abilities.

Human evolution

• Homo ergaster & erectus: First fully bipedal, large-brained, migrated out of Africa.

• Homo heidelbergensis: Evolved from H. erectus, similar to H. sapiens, large-animal hunters.

• Neanderthals: Evolved from H. heidelbergensis, coexisted with H. sapiens, interbred.

• Denisovans: Distinct group, interbred with Neanderthals and humans.

• Homo sapiens: Evolved in Africa ~200 kya.

Derived traits of chordate clades

• Cephalochordata: Notochord extends into head.

• Urochordata: Notochord and nerve cord in larvae.

• Vertebrata: Vertebral column, cranium, complex nervous system, endoskeleton, paired appendages, neural crest cells.