28: Phylogenies and the History of Life

Question 1

phylogeny

Answer 1

The evolutionary history of a group of organisms.

Question 2

phylogenetic tree

Answer 2

A branching diagram that depicts the evolutionary relationships among species or other taxa.

Question 3

tree of life

Answer 3

The phylogenetic tree that includes all organisms.

Question 4

branches

Answer 4

(1) A part of a phylogenetic tree that represents populations through time. (2) Any extension of a plant’s shoot system.

Question 5

nodes

Answer 5

(1) In animals, any small thickening (e.g., a lymph node). (2) In plants, the part of a stem where leaves or leaf buds are attached. (3) In a phylogenetic tree, the point where two branches diverge, representing the point in time when an ancestral group split into two or more descendant groups. Also called fork.

Question 6

tips

Answer 6

The end of a branch on a phylogenetic tree. Represents a specific species or larger taxon that has not (yet) produced descendants – either a group living today r a group that ended in extinction. Also called terminal node.

Question 7

character

Answer 7

Any genetic, morphological, physiological, or behavioral characteristic of an organism to be studied.

Question 8

outgroup

Answer 8

A taxon that is closely related to a particular monophyletic group but is not part of it.

Question 9

ancestral trait

Answer 9

A trait found in the ancestors of a particular group.

Question 10

derived trait

Answer 10

A trait that is clearly homologous with a trait found in an ancestor of a particular group, but that has a new form.

Question 11

cladistic approach

Answer 11

A method for constructing a phylogenetic tree that is based on identifying the unique traits (shared, derived characters, called synapomorphies) or each monophyletic group.

Question 12

synapomorphy

Answer 12

A shared, derived trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors. Useful for inferring evolutionary relationships.

Question 13

monophyletic group

Answer 13

An evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called clade or lineage.

Question 14

parsimony

Answer 14

The logical principle that the most likely explanation of a phenomenon is the most economical or simplest. When applied to comparison of alternative phylogenetic trees, it suggests that the one requiring the fewest evolutionary changes is most likely to be correct.

Question 15

homology

Answer 15

(adjective: homologous) Similarity among organisms of different species due to their inheritance from a common ancestor. Features that exhibit such similarity (e.g., DNA sequences, proteins, body parts) are said to be homologous.

Question 16

homoplasy

Answer 16

(adjective: homoplastic) Similarity among organisms of different species due to reasons other than common ancestry, such as convergent evolution. Features that exhibit such similarity (e.g., the wings of birds and bats) are said to be homoplastic, or convergent.

Question 17

convergent evolution

Answer 17

The independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and a similar way of life.

Question 18

SINEs (short interspersed nuclear elements)

Answer 18

The second most abundant class of transposable elements in human genomes; can create copies of itself and insert them elsewhere in the genome.

Question 19

fossil

Answer 19

Any physical trace of an organism that existed in the past. Includes tracks, burrows, fossilized bones, casts, and so on.

Question 20

fossil record

Answer 20

All of the fossils that have been found anywhere on Earth and that have been formally described in the scientific literature.

Question 21

paleontologists

Answer 21

Scientists who study the fossil record and the history of life.

Question 22

Precambrian

Answer 22

The interval between the formation of the Earth, about 4.6 billion years ago, and the appearance of most animal groups about 542 million years ago. Unicellular organisms were dominant for most of the era, and oxygen was virtually absent for the first 2 billion years.

Question 23

Paleozoic era

Answer 23

The interval of geological time, from 542 million to 251 million years ago, during which fungi, land plants, and animals first appeared and diversified. Began with the Cambrian explosion and ended with the extinction of many invertebrates and vertebrates at the end of the Permian period.

Question 24

Mesozoic era

Answer 24

The interval of geologic time, from 251 million to 65.5 million years ago, during which gymnosperms were the dominant plants and dinosaurs the dominant vertebrates. Ended with extinction of the dinosaurs (except birds).

Question 25

Cenozoic era

Answer 25

The most recent interval of geologic time, beginning 65.5 million years ago, during which mammals became the dominant vertebrates and angiosperms became the dominant plants.

Question 26

adaptive radiation

Answer 26

Rapid evolutionary diversification within one lineage, producing many descendant species with a wide range of adaptive forms.

Question 27

Cambrian explosion

Answer 27

The rapid diversification of animal body types and lineages that occurred between the species present in the Doushantuo faunas (around 570 mya), Ediacaran faunas (565-542 mya), and the Early Cambrian faunas (525-515 mya).

Question 28

fauna

Answer 28

All the animal species characteristic of a particular region, period, or environment.

Question 29

mass extinction

Answer 29

The extinction of a large number of diverse evolutionary groups during a relatively short period of geologic time (about 1 million years). May occur due to sudden and extraordinary environmental changes.

Question 30

background extinction

Answer 30

The average rate of low-level extinction that has occurred continuously throughout much of evolutionary history.