Words

What are Lagerstätten and why are they significant in paleontology?

Lagerstätten are sedimentary deposits that exhibit extraordinary fossil preservation, providing insight into the ancient ecosystems.

What is the Burgess Shale known for?

The Burgess Shale is known for its exceptional fossil find of soft-bodied organisms from the Cambrian period.

What is the difference between absolute dating and relative dating?

Absolute dating provides a specific age of a rock or fossil, while relative dating determines the relative order of events without giving a specific age.

What principle states that in undisturbed sedimentary rocks, the oldest layers are on the bottom?

The principle of superposition.

What does the principle of lateral continuity suggest?

Layers of sediment initially extend laterally in all directions; they are later disrupted but can be correlated across distances.

What is the significance of index fossils in geology?

Index fossils are used to identify and date the layers of rock in which they are found based on their unique features and wide distribution.

What is carbon dating primarily used for?

Carbon dating is primarily used to date organic materials that are up to about 50,000 years old.

What is the geologic time scale?

The geologic time scale is a timeline that organizes Earth’s history into different intervals based on geological and biological events.

Define monophyletic group in phylogeny.

A monophyletic group includes an ancestor and all its descendants, representing a complete branch of life.

What is a clade?

A clade is a group of organisms that includes a common ancestor and all its descendants.

What does the term 'most recent common ancestor' (MRCA) refer to?

MRCA refers to the latest individual from which all the organisms in a group are directly descended.

What is a synapomorphy?

A synapomorphy is a shared derived characteristic that is used to determine evolutionary relationships.

What does homoplasy mean in evolutionary biology?

Homoplasy refers to a trait that is similar between species but was not inherited from a common ancestor.

Define vestigial structures.

Vestigial structures are anatomical features that have lost most or all of their original function in the course of evolution.

What does evolutionary reversal mean?

Evolutionary reversal is when a derived trait reverts back to an ancestral state.

What is phylogeny?

Phylogeny is the study of the evolutionary history and relationships among individuals or groups of organisms.

What is the difference between ancestral state and derived state in characters?

Ancestral state refers to the original trait present in a common ancestor, while derived state refers to a trait that has evolved from the ancestral state.

fossil

Any preserved remains, impression, or trace of any once-living thing from a past geological age.

Lagerstätten

A sedimentary deposit that exhibits extraordinary fossil richness and completeness with exceptional preservation of soft tissues.

Burgess Shale

A famous Lagerstätte in the Canadian Rockies known for its exceptional preservation of soft-bodied marine organisms from the Middle Cambrian period.

absolute dating

A method of estimating the age of an object or event in years using radioactive decay.

relative dating

A method of determining the relative order of past events without necessarily determining their absolute age.

geologic time scale

A system of chronological dating that relates geological strata (stratigraphy) to time, used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in Earth history.

superposition

Geological principle stating that in an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.

lateral continuity

Geological principle stating that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous.

original horizontality

Geological principle stating that layers of sediment are originally deposited horizontally under the action of gravity.

cross-cutting

Geological principle stating that if a fault or other body of rock cuts through another body of rock, then the feature that cuts across is younger than the feature it cuts.

index fossil

A fossil that is useful for dating and correlating the strata in which it is found, due to its widespread occurrence and restricted time range.

carbon dating

A method for determining the age of an object containing organic material by using the properties of radiocarbon ($C^{14}$), a radioactive isotope of carbon.

uranium-lead dating

A radiometric dating method that uses the decay of uranium isotopes ($U^{238}$ and $U^{235}$) to lead isotopes to determine the age of rocks and minerals.

potassium-argon dating

A radiometric dating method that measures the decay of the radioactive isotope potassium-40 ($K^{40}$) into argon-40 ($Ar^{40}$) to date rocks and minerals.

Precambrian Eon

The earliest eon of Earth's history, lasting from the formation of the Earth about 4.6 billion years ago to the beginning of the Cambrian Period about 541 million years ago.

Phanerozoic Eon

The current eon in Earth's history, covering the last 541 million years, characterized by abundant animal and plant life.

phylogeny

The evolutionary history of a species or group of related species.

tips

The ends of branches in a phylogenetic tree, representing living or extinct taxa.

branches

Lines on a phylogenetic tree that represent lineages or ancestral populations evolving through time.

nodes

Points on a phylogenetic tree where branches diverge, representing common ancestors.

internal nodes

Nodes within a phylogenetic tree that represent hypothetical ancestors that gave rise to two or more descendant lineages.

monophyletic

A group of organisms that consists of a common ancestor and all of its descendants (a clade).

clade

A group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics; a monophyletic group.

paraphyletic

A group of organisms that includes a common ancestor but not all of its descendants.

outgroup

A taxon on a phylogenetic tree that is more distantly related to the ingroup (taxa being studied) than any ingroup member is to another ingroup member, used for comparison.

taxon (taxa)

A taxonomic group of any rank, such as a species, family, or class (plural: taxa).

most recent common ancestor (MRCA)

The most recent individual from which all organisms in a group are directly descended.

character

A feature or trait of an organism used in phylogenetic analysis (e.g., presence of wings, number of limbs).

character state

The specific condition or form of a character (e.g., ancestral state: no wings; derived state: presence of wings).

ancestral state

A character state that was present in the common ancestor of a group.

derived state

A character state that evolved recently in a lineage and is not present in the common ancestor.

synapomorphy

A shared derived character state that distinguishes a clade from other groups.

homoplasy

A character shared by a set of species but not present in their common ancestor, resulting from convergent evolution, parallel evolution, or evolutionary reversal.

convergent evolution

The independent evolution of similar features in species of different lineages.

evolutionary reversal (= character reversal)

The reversion of a derived character state to a more ancestral state.

vestigial

Refers to a structure or organ that has lost all or most of its original function in a species through evolution.

symplesiomorphy

A shared ancestral character state that is not informative for defining a clade because it is present in older ancestors.

sister group

Two descent groups (clades or species) that are each other's closest relatives, sharing a unique common ancestor not shared by any other group.