Lecture 3: Paleobiology and Macroevolution

Flashcards covering key concepts from the Paleobiology and Macroevolution lecture notes.

What is paleobiology and macroevolution?

Fields studying the history of life through fossils and long-term evolutionary patterns across lineages and ecosystems.

Why is the fossil record incomplete?

Because soft-bodied organisms fossilize poorly, many species were rare or locally distributed, sediments may not accumulate in their habitats, and fossils degrade over time.

What information can fossils reveal about life on Earth?

Morphology, ecology, timing of evolutionary events, geographic distributions, and indirect data on behavior, physiology, and ecology.

What drives plate tectonics and continental drift?

Mantle convection moving rigid plates; supercontinents form and break apart over millions of years.

What is a disjunct distribution?

A distribution where related populations live in widely separated geographic areas, often due to dispersal or vicariance.

What is adaptive radiation?

Rapid diversification of a lineage into multiple species occupying different ecological niches after colonization or a key innovation.

What are mass extinctions?

Episodes of large-scale species loss in a short geological time, distinct from background extinction.

What are the gradualist and punctuated equilibrium hypotheses?

Gradualism predicts slow, continuous morphological change; punctuated equilibrium predicts long periods of stasis punctuated by rapid speciation.

How can allometric growth produce morphological novelties?

Different parts of an organism grow at different rates, creating new shapes and proportions over time.

What is exaptation?

The evolution of a trait for one function that is co-opted for another; e.g., feathers initially for insulation or display, later aiding flight.

What is the genetic tool kit?

A set of hundreds of conserved homeobox genes that regulate development across animals, including Hox genes.

What are Hox genes?

Homeobox genes that govern the anterior-posterior body plan and segment identity.

What is Pax-6?

A gene involved in the development of eyes or light-sensing organs across animals.

What is radiometric dating?

Estimating the age of rocks by measuring decay of unstable parent isotopes to daughter products with known half-lives.

What is a half-life?

The time required for half of a radioactive parent isotope to decay.

Which rocks are best for radiometric dating?

Volcanic rocks; most fossils are found in sedimentary rocks.

What is relative dating?

Determining the age of fossils by their order in undisturbed strata; youngest on top.

What is carbon-14 dating used for?

Dating organic matter up to about 50,000 years; based on 14C decay to 14N with a half-life of 5,730 years.

How is geological time structured?

Organized into eons, eras, periods, and epochs; Phanerozoic eon includes Paleozoic, Mesozoic, and Cenozoic.

What marks the end of the Cretaceous and mass extinction?

KT extinction event caused by asteroid impact (Chicxulub) with an iridium layer and a large crater.

What does the iridium layer signify?

Evidence of asteroid impact at the end of the Cretaceous.

What climatic effects can volcanic eruptions and asteroid impacts have?

Block sunlight with ash/dust causing cooling; impacts can also alter climate through material in the atmosphere.

What is continental drift and plate tectonics?

Movement of Earth's crustal plates due to mantle convection; explains the movement of continents over time.

What was Pangaea and its breakup sequence?

A supercontinent that split into Laurasia and Gondwana, which later fragmented into today’s continents.

What is a biogeographic realm?

A large geographic region with distinctive plant and animal biotas; Wallace defined six realms, later refined to 11 major zoogeographic realms.

What is convergent evolution?

Independent evolution of similar forms in distantly related lineages due to similar environments.

Give an example of convergent evolution.

Cacti in the Americas resemble African spurges; marsupial mammals in Australia resemble placental mammals elsewhere.

What is the history of biodiversity in terms of adaptive radiations and extinctions?

Biodiversity changes through adaptive radiations and extinctions; mass extinctions open opportunities for subsequent radiations.

What is background extinction?

Slow, ongoing extinction rate driven by organisms poorly adapted as environments change.

What are mass extinctions and name two famous ones?

Episodes of high extinction rates; Permian and Cretaceous (K-T) extinctions.

What caused the Permian extinction?

A chain of events leading to severe climate warming due to greenhouse gases from ongoing eruptions.

What caused the KT extinction?

Asteroid impact near the Yucatán; dust cloud blocked sunlight; supported by iridium layer and Chicxulub crater.

What happens after mass extinctions?

Surviving lineages may undergo adaptive radiation, filling newly opened ecological niches and increasing biodiversity.

What is transitional fossil and its significance?

Fossils showing intermediate features linking major groups; support gradual evolution or punctuated models.

Describe the horse evolution sequence.

Hyracotherium → Mesohippus → Merychippus → Pliohippus → Equus; trends include larger body size and limb adaptations for speed.

What is paedomorphosis?

Development of reproductive maturity in an organism with juvenile morphology; retention of juvenile traits into adulthood.

What is heterochrony?

Changes in the timing of developmental events that alter morphology across related species.

What is exaptation in the origin of feathers?

Feathers likely evolved as modifications of scales and were later co-opted for flight; seen in fossils like Archaeopteryx and Microraptor.

What is the significance of the genetic toolkit in development?

Conserved set of homeobox genes controlling development; many are hundreds of millions of years old and regulate body plans.

Why can different body plans arise if the genetic toolkit is shared?

Differences in gene regulation, timing, and interaction of developmental genes lead to diverse morphologies.