Earth and Life History Comprehensive Vocabulary

This set of vocabulary cards covers key concepts in paleontology and Earth history, including mass extinctions, ecological metrics, evolutionary morphology, fossil sites like the Burgess Shale, avian and hominin evolution, and major geological-biological events.

Background extinction

The "normal" or expected rate of extinction consistent with previously established trends.

Mass extinction (Hallam & Wignall)

Extinction of a significant proportion of the world's biota in a geologically insignificant period of time.

Mass extinction working definition

Global in significance; loss of > 15\% of familial diversity; occurring in < 15\,Myr.

Myr

Millions of years (a duration).

Ma

Millions of years ago (a point in time).

Late Ordovician extinction

$\sim 445\,Ma$; $\sim 85\%$ marine species lost; caused by glaciation and sea level drop of $\sim 100\,m$.

Late Devonian extinction

$\sim 372\text{--}359\,Ma$; $70\text{--}75\%$ species lost; multiple pulses; ocean oxygen drop and global cooling.

End-Permian extinction

$\sim 250\,Ma$; largest ever; $\sim 96\%$ marine species; caused by Siberian Traps volcanism and $CO_2$ release.

End-Triassic extinction

$\sim 201\,Ma$; $76\%$ species lost; caused by CAMP volcanism during Pangaea breakup.

K-Pg extinction

$\sim 66\,Ma$; caused by Chicxulub asteroid impact; all non-avian dinosaurs extinct.

Iridium anomaly

$300 \times$ normal concentration at K-Pg boundary; found at $100+$ localities; evidence of asteroid impact.

Shocked quartz

Quartz with high-pressure parallel fractures; evidence of asteroid impact.

Chicxulub crater

An impact site identified in the late 1980s on the Yucatan Peninsula that is $\sim 180\,km$ across.

Siberian Traps

Massive volcanic province; cause of End-Permian extinction via $CO_2$ release.

CAMP

Central Atlantic Magmatic Province; cause of End-Triassic extinction; dated $\sim 201\,Ma$ across multiple continents.

Deccan Traps

Indian volcanic province contributing to K-Pg extinction; thickness > 2000\,m; volume $\sim 1.5\,million\,km^3$.

Ecological community

Organisms living in a local area that can interact directly in space and time.

Ecosystem

Organisms living and interacting in a local area plus their physical environment.

Fossil assemblage

Fossils preserved together in a single bed in the fossil record.

Time-averaging

Mixing of remains from different time periods into a single fossil layer.

Bioturbation

Disturbance of sediments by organisms (e.g. burrowing worms); major cause of time-averaging.

Live-dead comparison

Comparing living organisms at a location to the time-averaged death assemblage at the same location.

Metacommunity

A set of local communities among which species can disperse.

Death assemblage

Collection of dead remains accumulated at a location over time; time-averaged.

Lagerstatten

Sites of exceptional soft tissue preservation.

Rarefaction

Method of standardizing diversity comparisons by subsampling assemblages to equal size.

Ichnofacies

Trace fossil assemblages that indicate sedimentary environment and water depth.

Ophiomorpha

Shoreface ichnofacies; sandy substrate; suspension feeders; low diversity.

Cylindrichnus

Offshore ichnofacies; sandy substrate; suspension and deposit feeders; medium diversity.

Teichichnus

Offshore ichnofacies; muddy sand; deposit feeders; high diversity.

Scolicia

Lower offshore ichnofacies; sandy/muddy substrate; deposit feeders; low diversity.

Zoophycos

Deep offshore ichnofacies; silty/muddy substrate; deposit feeders; low-medium diversity.

Photic zone

$0\text{--}200\,m$ depth; light penetrates; fuels photosynthesis.

Aphotic zone

$200\text{--}2500\,m$ depth; no light; food sinks from above.

Abyssal zone

$2500\text{--}6000\,m$; deepest ocean floor.

Benthic zone

On the seafloor.

Pelagic

In the water column.

Neritic zone

Shallow coastal waters over continental shelf.

Planktonic

Floating in surface waters; carried by currents.

Nektonic

Actively swimming in water column.

Infaunal

Living inside sediment.

Epifaunal

Living on sediment surface.

Neogloboquadrina pachyderma

Foraminifera that coils left in cold water and right in warmer water; used as paleothermometer.

Carroll et al. 2003

Studied shells and found median time-averaging $\approx 300\,years$; some up to $3000+$ years.

Species richness

Simple count of number of species.

Evenness

How evenly individuals are distributed among species.

Shannon Index

Diversity metric combining richness and evenness.

Alpha diversity

Diversity within a single local community or sample.

Beta diversity

Difference in diversity between communities; how much composition changes between places.

Gamma diversity

Total diversity across a whole region.

Species-area relationship

Larger areas contain more species; consistent and predictable.

Latitude-diversity gradient

Species diversity highest in tropics; declines toward poles.

Disparity

Diversity of body plans/morphologies; distinct from species richness.

Sepkoski curve

Plot of marine family diversity through time; shows three evolutionary faunas.

Cambrian fauna (Cm)

Trilobites and early arthropods; peaked early then declined.

Paleozoic fauna (Pz)

Brachiopods, crinoids, corals; dominated Paleozoic; devastated by Permian extinction.

Modern fauna (Md)

Mollusks, fish, echinoids; rose after Permian extinction; dominates today.

Bush et al. 2007

Framework defining ecological modes of life across three axes: tiering, motility, and feeding.

Tiering axis

Pelagic $\rightarrow$ Erect $\rightarrow$ Surficial $\rightarrow$ Semi-infaunal $\rightarrow$ Shallow infaunal $\rightarrow$ Deep infaunal.

Motility axis

Fully motile $\rightarrow$ Facultatively motile $\rightarrow$ Non-motile.

Feeding axis

Suspension $\rightarrow$ Surface deposit $\rightarrow$ Mining $\rightarrow$ Grazing $\rightarrow$ Predatory $\rightarrow$ Other.

Homologue

Structure shared within lineages due to common ancestry.

Analogue

Similar structure evolved independently in different lineages; same function, different origin.

Spandrel

Trait that exists as a byproduct of another adaptation; not itself selected for.

Adaptation

Trait shaped by natural selection for its current function.

Exaptation

Trait that originated for one function but was co-opted for another.

Coaptation

Exaptation where structure shifts from one function to another (e.g. swim bladder $\rightarrow$ lungs).

Heterochrony

Change in timing, rate, or duration of developmental processes relative to ancestors.

Paedomorphism

Retention of juvenile traits into adulthood.

Neoteny

Development slowed or delayed; retains juvenile features (e.g. axolotls).

Progenesis

Sexual maturity accelerated; reproduces while developmentally juvenile.

Peramorphism

Adult features develop further or longer than in ancestors (e.g. Irish elk antlers).

Isometry

Trait grows proportionally to body size; log-log slope $= 1$.

Positive allometry

Trait grows faster than body size; slope > 1 (e.g. crab claws).

Negative allometry

Trait grows slower than body size; slope < 1 (e.g. human head relative to body).

Functional morphology

Study of how morphological form relates to biological function.

Phylogenetic bracketing

Using evolutionary position bracketed by living relatives to infer unpreserved traits.

Morphodynamics

Framework where form is shaped by biological function + morphogenetic fabrication + phylogenetic tradition.

Pakicetus

$\sim 50\text{--}55\,Ma$; earliest whale ancestor; four-legged; freshwater habitat.

Ambulocetus

Semi-aquatic whale ancestor; freshwater habitat.

Dorudon

$\sim 37\,Ma$; fully aquatic whale; vestigial hind limbs; nasal opening shifted back.

Adaptive radiation

Rapid diversification of one ancestral lineage into many forms each occupying different ecological niches.

Novelty

A new morphological structure.

Innovation

A novelty that opens access to a new adaptive zone and enables a radiation.

Explosive phase

Rapid divergence; quantum evolution; many intermediate forms; triggered by new adaptive zone.

Normal phase

Gradual phyletic evolution; reduced variation; no intermediate forms.

Ediacaran biota

Soft-bodied organisms $\sim 575\text{--}539\,Ma$; preserved as impressions.

Dickinsonia

Oval ribbed Ediacaran organism.

Spriggina

Possibly early arthropod/trilobite precursor; may be uncalcified trilobite.

Rangeomorphs

Fractal branching Ediacaran organisms; possibly osmotrophic feeders.

Treptichnus pedum

First complex vertical burrow; defines base of Cambrian at Fortune Head Newfoundland (GSSP).

GSSP

Global Boundary Stratotype Section and Point; official marker defining a geological boundary.

Ichnofabric Index

Measure of burrowing intensity in sediment; Early Cambrian $\sim 3$; Late Ordovician $\sim 5$.

Small Shelly Fauna

Earliest biomineralized organisms; diverse morphologies; tubes, cones, plates, spicules.

Burgess Shale

$\sim 508\,Ma$; British Columbia; exceptional soft tissue preservation in anoxic mud.

Opabinia

Burgess Shale organism with five eyes and a frontal grasping appendage.

Hallucigenia

Burgess Shale lobopodian; spines and tentacles; related to velvet worms.

Anomalocaris

Burgess Shale apex predator; up to $1\,m$ long.

Wiwaxia

Burgess Shale organism; scaly and spiny; likely mollusk relative; preserved radula.

Halkieria

Burgess Shale organism; covered in sclerites with shell caps at each end.