cladistics making and testing hypotheses of relationship. 28 may 2015 cladistics2108.ppt1

Cladistics

Making and testing hypotheses of relationship.

28 May 2015 Cladistics2108.ppt 1

HYPOTHESIS of relationship



Cladistics

• Grouping by common descent.

• 3-taxon statement: A and B are more

closely related to each other than either is to C.


MONOPHYLETIC group(s):

• Grouping of species including all descendants of a common ancestor and the common ancestor.


POLYPHYLETIC group

• [Linnaeus] states as follows: “On account of their warm bilocular heart, their lungs, their moveable eyelids, their hollow ears, penem intrantem feminam mammis lactantem, …”

• “I take the good old-fashioned ground that the whale is a fish… a whale is a spouting fish with a horizontal tail.” o Melville, H. 1851. Moby Dick, Chapter XXXII.


POLYPHYLETIC group(s)

• Include one or more species not descended from the same ancestor as the other members.

• TO BE AVOIDED!!!!!!!


• BUT, lineages, true common ancestors, are unknown. ALL we really know are modern species.

• Fossil specimens could be ancestors, or extinct side branches, of the family tree.


HOW TO RECOGNIZE A MONOPHYLETIC GROUP:

• Classification by shared derived characters only. • primitive &/or convergent similarities will

mislead.


Shared derived character:

= Homology

= “Distinguishing character.” Trait, characteristic, or feature of a group found in every member of the group and not in any other group.


Cladistics

• Avoids bias of researcher, authority.

• Grouping (classification) = scientific hypothesis.Testable by congruence of charactersRepeatable.

Cladistics

• Reading a cladogram• X-axis

• Y-axis

• Line, line segment

• Node, branching point

• Line end


Cladistics


cladistics making and testing hypotheses of relationship. 28 may 2015 cladistics2108.ppt1

Documents

ppt1 slide

ppt11 slide

ppt2 slide

ppt10 cladistics

ppt3 cladistics

common descent

true common ancestors

derived characters