CVA - Unit 1. Vertebrate History and Lineages

Phylogeny

the evolutionary history of lineages

Ontogeny

the development of individuals

Metamerism

segmentation of body structures (along the anteroposterior axis)

Bilateral symmetry

distinct anterior / posterior regions; midsagittal plane can divide the body into mirrored halves

Cephalization

the increased localization of nerves and sensory structures into a distinct, dominant head

Adaptation

a hereditary modification of a phenotype that increases the probability of survival

Preadaptation

structure or behavior possesses the necessary form or function before the biological role arises

Morphologies can be similar based on which three criteria?

1. Homology

2. Analogy

3. Homoplasy

Homology

similarity based on common ancestry (often detected via embryology)

Analogy

similarity of function

Homoplasy

similarity of resemblance (usually refers to similarities in structure that do NOT result from common evolutionary origin)

_______ and ______ evolution often lead to homoplasy.

Convergent, parallel

Parallelism

closely related species that diverged relatively recently develop similar specializations

Convergent evolution (convergence)

distantly related and morphologically dissimilar species become more similar in descendants

Heterochrony

changes in the relative timing of developmental processes in descendants relative to ancestral species

Paedomorphosis

retention of embryonic or larval characteristics into adulthood

Peramorphosis

development of structures is extended, creating new morphologies

Clade

all the descendants of a common ancestor

Non-rank nomenclature

names assigned to lineages originating from each branch point (node)

Plesiomorphic traits

ancestral (“primitive”) traits

Symplesiomorphy

shared ancestral characteristics

Apomorphic traits

derived traits

Autapomorphy

unique derived characteristics

Synapomorphy

shared derived characteristics

(These are the ONLY traits that provide information re: phylogenetic relationships)

Parsimony

tendency towards the simplest explanation (“Occam’s razor”)

Principle of parsimony

fewest number of changes from ancestral to derived trait is most parsimonious

Monophyletic group

ALL descendants of a common ancestor are included

Paraphyletic group

includes common ancestor, but one or more descendants are omitted

Polyphyletic group

members do NOT share a common ancestor

Crown group

smallest clade that includes ALL living members of a group and any fossils (usually the top of the phylogenetic tree)

Stem group

extinct basal members of a clade not included in the crown group, (often lacking some synapomorphies) but are more closely related to the crown group than any other group

Why can phylogenies be considered “hypotheses”?

They are based on incomplete data and are subject to change with new evidence.

Remember: The fossil record is NOT complete. It takes a while to become a fossil. The information we have today could change tomorrow!

Why can traits be considered primitive, but not living organisms?

Organismal phenotypes are often a mosaic, or a mishmash, of ancestral and derived traits. We can use “primitive” or “ancestral” to describe the traits, but not the living organism.

A simple mono/pary/polyphyly diagram. :)