BIOL 1020U Lecture Notes - Lecture 23: Library Classification, Tetrapod, Reference Group
Phylogenies and Fossils Lecture
Textbook Reference: Chapter 23 in Biology How Life Works (2nd ed.)
Sections 23.1 – 23.2; pp.464 to 474
Required Reading: Required Reading: Sections 23.3 and 23.4
(pages 474 to 483)
Systematics
What is systematics?
Study of biological diversity and its origins
What is the main difference between phylogenetics and taxonomy?
Phylogeny – study of evolutionary and genetic relationships among organisms uses
anatomical or molecular features to depict relationships as phylogenetic trees
Taxonomy – classification and naming of organisms provides hierarchical
classifications in more and more inclusive groups
Phylogeny
•The process of speciation can be depicted in a phylogenetic tree
Can be depicted in phylogenetic trees – order across top does not mean anything –
does not mean one came before the other more
interested in the branch points and the
relativeness to each other
On a phylogenetic tree:
•What do the branches
represent?
Diverging populations
•What do nodes represent?
Last common ancestors branch points
•What are descendent
species?
Plant or animal descending from particular
species
Phylogenetic Trees are Hypotheses
•What does the branching
order represent?
Hypothesizes the evolutionary relationships within a group
•The tree below proposes:
1.Closest living relatives of birds are crocodiles and alligators
2.Closet relatives of all tetrapod (4-legged) vertebrates are lungfish
Page | 1
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Sister Groups
•What are sister groups?
2 groups considered to be each other’s’ closest relatives if they share a common
ancestor not shared by any other group
How are sister groups determined?
By looking to see how recently 2 groups share a common ancestor (node) can
be rotated without changing evolutionary relationships
Explain why the three trees below are the same?
Each show that birds are closely related to alligators and crocodiles because
they are in the same node – nodes can be rotated without changing evolutionary
relationships
Page | 2
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Practice:
•Are these four trees the
same? Explain:
Ancestor group to everyone are frogs
Dogs and humans are sister groups to each
other
C and A – rotation of animals, but is stilling
telling you the same thing about relatedness
•Does either of these two trees
indicate that humans are more closely
related to lizards than mice? Explain.
No, both trees indicate that humans
are more closely related to mice, the
nodes are just rotated
Key point:
•Information about evolutionary relationships is found in the order of the
nodes over time, not the order of the groups along the tips
•Evolution is not progressive toward perfection or complexity
Monophyletic, Paraphyletic, and Polyphyletic Groups
•What is the goal in phylogenetics?
To integrate evolutionary history with taxonomy classification
•Only monophyletic groups reflect evolutionary relationships. Why?
only they include all descendants of a common ancestor
Page | 3
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Document Summary
Textbook reference: chapter 23 in biology how life works (2nd ed. ) Sections 23. 1 23. 2; pp. 464 to 474. Required reading: required reading: sections 23. 3 and 23. 4 (pages 474 to 483) Phylogeny study of evolutionary and genetic relationships among organisms uses anatomical or molecular features to depict relationships as phylogenetic trees. Taxonomy classification and naming of organisms provides hierarchical classifications in more and more inclusive groups. Phylogeny: the process of speciation can be depicted in a phylogenetic tree. Can be depicted in phylogenetic trees order across top does not mean anything does not mean one came before the other more interested in the branch points and the relativeness to each other. 1. closest living relatives of birds are crocodiles and alligators. 2. closet relatives of all tetrapod (4-legged) vertebrates are lungfish. 2 groups considered to be each other"s" closest relatives if they share a common ancestor not shared by any other group.
