Chapter 18: Evolution and the Fossil Record

Taphonomy

Study of the fossilization process

Phyletic Transformation (Anagenesis)

The evolution of a new morpho-species by the gradual transformation of an ancestral species, without a speciation or splitting event taking place

Synapsid

A clade of amniote that ultimately gave rise to the mammals Inaccurately described as mammal-like reptiles

Cynodonts

A clade of amniotes represented among extant organisms by the mammals Nested within the larger therapsid clade, which is nested within the still-larger synapsid clade

Mass Extinctions

A large-scale, sudden extinction event that is geographically and taxonomically widespread

Morphospace

Actual or potential range of morphologies encompassed

Amber and Freezing

Among the least altered remains available to paleontologists, but they are rare. Viscous plant resins can harden into amber, preserving insects trapped inside so well that wing veins are visible

Plesiomorphies

An evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group (compare apomorphy) and therefore cannot be used as a diagnostic or defining character for the group

Permineralization and Replacement

Common modes of fossilization and can form when structures are buried in sediments and dissolved minerals either replace the original mineral content or precipitate in and around it

Trace Fossils

Differ from other types of fossils, which are collectively termed body fossils, in that trace fossils record behavior instead of form

Background Extinctions

Extinctions that are not part of mass extinction events Thought to be due to typical types and rates of environmental change or species interactions as opposed to the extraordinary environmental changes that occur during mass extinctions

Disparity

In paleontology, that portion of the universe of theoretically possible morphologies actually occupied by a species or clade The variation observed within a taxon as compared to the possible variation

Stasis

Lack of change

Macroevolution

Large evolutionary change, usually in morphology Typically refers to the evolution of differences among populations that would warrant their placement in different genera or higher-level taxa

Extant

Living today

Explain why these are common in the fossil record: marine-dwelling forms burrowing species recent organisms pollen grains

Marine-dwelling forms are common because after these organisms die, their bodies fall to the bottom of the ocean or lake, giving them a higher chance to be buried and therefore a slower decomposition. Burrowing species live underground, so they are already "pre-buried." When they die, they remain buried underground, and their decomposition slows. As recent organisms have only recently died, it is very easy to find their fossils because they have not yet decomposed fully or have been eroded, unlike early fossils. Pollen grains have a tough outer cover made of cellulose, which resists decomposition.

Compare and contrast mass extinctions and background extinctions. How do their size and geographic and taxonomic extent differ?

Mass extinctions killed off 60% or more species alive in a given time period. They are much quicker than background extinction, and include a wide range of species. It happens rapidly compared to the lifespan of the taxa. Background extinctions, however, occur at a more natural rate and wipe out around 96% of living species. Background extinctions are constant and do not depend on the time period of the taxa. Within clades, the rates are constant, but across clades, they can vary.

Natural Molds and Casts

Originate when remains decay after being buried in sediment. Molds consist of unfilled spaces, whereas casts form when new material infiltrates the space, fills it, and hardens into rock. Molds and casts preserve information about surface shape, but not internal details

Synapomorphies

Shared, derived character In a phylogenetic analysis, synapomorphies are used to define clades and distinguish them from outgroups

Molecular Clock

The hypothesis that base substitutions accumulate in populations in a clock-like fashion That is, as a linear function of time

Punctuated Equilibrium

The hypothesis that evolution over geologic time has typically been characterized by rapid morphological change during speciation interspersed with long periods of stasis

Biotic Replacement

Used in paleontology to describe events in which one clade disappears in the fossil record and another clade takes its place Can be competitive, as when the new clade ecologically displaces the old, or noncompetitive, as when a mass extinction is followed by an evolutionary radiation