BIOL 300 Exam 1 - George Mason University (You got this!!)

Root

The base of the phylogenetic tree, is the most recent common ancestor of ALL taxa

Node

In phylogenetic trees, the point where a branch splits, representing the common ancestor from which the descendant species diverged

Taxon (Plural: Taxa)

A biological group given a name (Ex: family, species, class, etc...)

Clade

A group of organisms evolved from a common ancestor

Sister species

Two species that are each other's closest relatives

Sister clades

Two clades that are each other's closest relatives

Lineage

A series of populations, species, or genes descended from a single ancestor over evolutionary time

Common ancestor

Ancestral organism shared by two or more lineages

Homology

A similarity between two or more features that is due to inheritance from a common ancestor

Synapomorphy

A trait that arose in the ancestor of a phylogenetic group and is present in all of its members, thus helping delimit and identify that group. Also known as a shared derived trait. (Ex: Mammals produce milk)

Ancestral trait

The trait originally present in the ancestor of a given group; may be retained or changed in the descendants of that ancestor

Derived trait

A trait that differs from from the ancestral trait (Ex: how marsupials are mammals but have pouches unlike most mammals)

Autapomorphy

Found in one taxon but not in the outgroup or any other taxons

Evolutionary reversal

The reappearance of an ancestral trait in a group that had previously acquired a derived trait (ex: how penguins lost the ability to fly)

Homoplasy

The presence in multiple groups of a trait that is not inherited from the common ancestor of those groups. Can result from convergent evolution, evolutionary reversal, or parallel evolution

Analogous trait

A trait that is morphologically and functionally similar to that of a different species but that arose from a distinct, ancestral condition

Ingroup

In a phylogenetic study, the group of organisms of primary interest

Outgroup

In phylogenetics, a group of organisms used as a point of reference for comparison with the groups of primary interest

Monophyletic

Pertaining to a group that consists of an ancestor and all of its descendants

Paraphyletic

Pertaining to a group that consists of an ancestor and some, but not all, of its descendants

Polyphyletic

Pertaining to a group consists of multiple distantly related organisms, and does not include the common ancestor of the group

Stratum (Plural: strata)

A layer of rock laid down at a particular time in the past

Sedimentary rock

Rock formed by the accumulation of sediment grains on the bottom of a body of water. Often contains stratified fossils that allow geologists and biologists to date evolutionary events relative to each other

Radioisotopes

A radioactive isotope of an element (Ex: C-14)

Background extinction rate

At any given time a certain number of species are going extinct (5-11%), but is balanced out by new species generated

Biogeography

The scientific study of the distribution and diversity of organisms across earth

Hadean Eon

4.6-4.5 bya

This eon represents the formation of Earth. Life wasn't present yet, but the Earth was cooling. Atmosphere has no free oxygen, but the oceans are forming. A ton of meteorites were hitting Earth constantly.

Archaean Eon

3.8 bya

Life originated in this eon. Prokaryotes specifically are thriving. Earth accumulates atmosphere but still barely any oxygen. Meteor impacts decrease dramatically.

Proterozoic Eon

2.5 bya

Atmospheric oxygen levels emerge, and photosynthesis, multicellular organisms and eukaryotes emerge. This extremely long eon contains the "snowball Earth" hypothesis, which hypothesized that the Earth was completely covered in ice for millions of years.

Cambrian Period (Paleozoic Era)

542 mya

Atmospheric oxygen levels approach levels found today and rapid diversification of multicellular organisms and diverse photosynthetic protists

Ordovician Period (Paleozoic Era)

488 mya

Massive glaciation where sea levels drop by 50 meters, this caused a mass extinction

Silurian Period (Paleozoic Era)

444 mya

Sea levels rise and two large land masses emerge. The climate is hot and humid. Jawless fish diversify and first ray-finned fishes; plants and animals colonize land

Devonian Period (Paleozoic Era

416 mya

Continents collide at the end of this period, jawed fishes diversify, first insects and amphibians, mass extinction probably at least partially caused by a meteor

Carboniferous Period (Paleozoic Era)

359 mya

Climate cools down, extensive fern/horsetail/giant club moss forests; first reptiles in this period, insects also diversify

Permian Period (Paleozoic Era)

299 mya

Extensive lowland swamps, oxygen levels are 50% higher than today, by the end Pangea is formed. Reptiles diversify, giant amphibians and insects are present, and the largest mass extinction takes place as oxygen levels drop rapidly

Triassic Period (Mesozoic Era)

251 mya

Pangea begins to drift apart; the climate is hot and humid. Early dinosaurs, first mammals, marine invertebrates diversify, mass extinction at the end of this period

Jurassic Period (Mesozoic Era)

201.6 mya

Two massive continents form, Laurasia in the north and Gondwana in the south. Warm climate, diverse dinosaurs and radiation of ray-finned fish. First fossils of flowering plants

Cretaceous Period (Mesozoic Era)

145.5 mya

Laurasian continents attached to one another; Gondwana begins to drift apart. Meteorites strikes near current Yucatan peninsula. Dinosaurs continue to diversify, with a mass extinction wiping them out at the end of this period

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