Macroevolution and the Fossil Record

This set of vocabulary flashcards covers key concepts of macroevolution, the processes and biases of the fossil record, radiometric dating techniques, and the transition of lineages from fish to tetrapods and dinosaurs to birds.

Macroevolution

Evolutionary processes occurring above the species level, including major phenotypic innovations, diversification patterns, and rates of speciation and extinction.

Fossilización Requirements

The rare combination of circumstances including rapid and complete burial after death, an anoxic environment, and stable sediment environments (often marine).

Taxonomic Bias

A systematic bias in the fossil record where organisms with hard body parts (bones, teeth, shells) are much more likely to fossilize than soft-bodied organisms.

Relative Dating

A method of determining the age of fossils using stratigraphic analysis, such as the principle that younger sediment layers lie above older ones.

Absolute Dating

The use of radiometric dating and molecular clocks to determine the specific numerical age of a sample.

Isotope

Variants of a chemical element that differ in their number of neutrons, such as $^{12}C$ and $^{14}C$.

Half-life

The constant rate at which a radioactive isotope decays, defined as the time it takes for $50\%$ of the parent isotope to decay into stable daughter isotopes.

Decay Constant ($L$)

The exponential constant representing the proportion of parent isotope $X$ decaying into daughter isotope $Y$ per unit of time, defined by the rate of change $dNx(t) / dt = -L Nx(t)$.

Potassium/Argon (K/Ar) Dating

A radiometric method for dating igneous rocks where $^{40}K$ decays into $^{40}Ar$; it is useful because $^{40}Ar$ gas escapes molten rock, ensuring the initial amount at $t=0$ is zero.

Superposition

One of Steno's laws of stratigraphy stating that younger sediment layers are deposited on top of older layers.

Bracket Dating

A method of estimating the age of fossils by dating the igneous rock layers (which are easier to date reliably) located above and below the sediment layer containing the fossil.

Crown Group

A group that includes all descendants of the latest common ancestor of all extant (living) taxa, including any extinct descendants of that ancestor.

Stem Groups

Extinct lineages that branch below the crown group in a phylogeny; they are not the ancestors of modern taxa but share some synapomorphies with them.

Exaptation

A biological adaptation where a trait that evolved to perform one function is later co-opted to perform a different function (e.g., feathers for insulation later used for flight).

Acanthostega

An early aquatic tetrapod possessing gills, lungs, and paddle-like limbs; it demonstrates that key tetrapod adaptations like the pelvic girdle and weight-bearing spine predated terrestrial life.

Archaeopterix

A famous fossil representing a stem-group bird that displays a mosaic of reptilian plesiomorphies and bird-like synapomorphies such as an opposable toe.

Time for Speciation (TFS)

The duration required for a pair of new species to complete the process of speciation and achieve full reproductive isolation.

Between-Speciation Interval (BSI)

A measure of how often new species pairs arise within a lineage over time.

Rate of Character Change ($r$)

A measurement of phenotypic evolution calculated using the formula $r = (\ln X_2 - \ln X_1) / \Delta t$.

Punctuated Equilibrium

A model proposed by Eldredge and Gould (1972) suggesting that phenotypic evolution occurs in rapid spurts often associated with speciation, followed by long periods of stasis.

Phyletic Gradualism

The view that phenotypic evolution is a steady, slow process of change that does not necessarily require the origin of new species.

Punctuated Gradualism

An evolutionary pattern where periods of rapid phenotypic change alternate with stasis, but the changes do not involve speciation events.