25.1 Tools for Studying Life’s History: Phylogenetic Trees

The branching evolutionary history of species or other groups of organisms is called a phylogeny.
A phylogenetic tree is a simplified diagram of this history.
Systematics is the discipline of biology that characterizes and classifies the relationships among all organisms on Earth.
The tree of life is the most universal of all phylogenetic trees.
Sister groups are two descendants that split from the same node and therefore are each other’ s closest relatives.
A useful character, or trait, is any heritable genetic, morphological, physiological, developmental, or behavioral characteristic that varies among the taxa to be studied.
Outgroup is a taxon that is not part of the taxonomic group being studied but is closely related.
An ancestral trait is a character that existed in an ancestor.
A derived trait is one that is a modified form of the ancestral trait, found in a descendant.
A synapomorphy is a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors.
Synapomorphies are important because they allow biologists to recognize monophyletic groups-also called clades or lineages.
A monophyletic group is an evolutionary unit that includes an ancestral species and all of its descendants, but no others.
Convergent evolution is the independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and lifestyles.

25.2 Tools for Studying Life’s History: The Fossil Record

Paleontologists are scientists who study fossils, pieces of physical evidence from an organism that lived in the past.
The fossil record is the total collection of fossils that paleontologists and amateur collectors have found throughout the world and archived in thousands of private and public collections.
The Paleozoic (“ancient life”) era begins with the appearance of most major animal lineages and ends with the obliteration of almost all multicellular life-forms at the end of the Permian period.
The Mesozoic (“middle life”) era begins with the end-Permian extinction events and ends with the extinction of the dinosaurs ( except birds) and other groups at the boundary between the Cretaceous period and Paleogene period.
The Cenozoic (“recent life”) era is divided into the Paleogene, Neogene, and Quaternary periods.

When a single lineage rapidly produces mαny descendant species with a wide range of adaptive forms, biologists say that an adaptive radiation has occurred.

A mass extinction refers to the rapid extinction of a large number of diverse species around the world.
Background extinction refers to the lower, average rate of extinction observed when a mass extinction is not occurring
Some researchers estimate that the current extinction rate is 100 or even 1000 times higher than the background extinction rate

The branching evolutionary history of species or other groups of organisms is called a phylogeny.
A phylogenetic tree is a simplified diagram of this history.
Systematics is the discipline of biology that characterizes and classifies the relationships among all organisms on Earth.
The tree of life is the most universal of all phylogenetic trees.
Sister groups are two descendants that split from the same node and therefore are each other’ s closest relatives.
A useful character, or trait, is any heritable genetic, morphological, physiological, developmental, or behavioral characteristic that varies among the taxa to be studied.
Outgroup is a taxon that is not part of the taxonomic group being studied but is closely related.
An ancestral trait is a character that existed in an ancestor.
A derived trait is one that is a modified form of the ancestral trait, found in a descendant.
A synapomorphy is a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors.
Synapomorphies are important because they allow biologists to recognize monophyletic groups-also called clades or lineages.
A monophyletic group is an evolutionary unit that includes an ancestral species and all of its descendants, but no others.
Convergent evolution is the independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and lifestyles.

Paleontologists are scientists who study fossils, pieces of physical evidence from an organism that lived in the past.
The fossil record is the total collection of fossils that paleontologists and amateur collectors have found throughout the world and archived in thousands of private and public collections.
The Paleozoic (“ancient life”) era begins with the appearance of most major animal lineages and ends with the obliteration of almost all multicellular life-forms at the end of the Permian period.
The Mesozoic (“middle life”) era begins with the end-Permian extinction events and ends with the extinction of the dinosaurs ( except birds) and other groups at the boundary between the Cretaceous period and Paleogene period.
The Cenozoic (“recent life”) era is divided into the Paleogene, Neogene, and Quaternary periods.

When a single lineage rapidly produces mαny descendant species with a wide range of adaptive forms, biologists say that an adaptive radiation has occurred.

A mass extinction refers to the rapid extinction of a large number of diverse species around the world.
Background extinction refers to the lower, average rate of extinction observed when a mass extinction is not occurring
Some researchers estimate that the current extinction rate is 100 or even 1000 times higher than the background extinction rate