Groups of organisms

Question 1

A taxon is…

Answer 1

A named group of organisms of any rank. For example, a taxon may be a kingdom or (if you believe in them), a species, a subspecies, etc.

Question 2

A monophyletic group is…

Answer 2

A group that contains a common ancestor and all of its descendants, e.g.
the Amniota.

Question 3

What is a paraphyletic group?

Answer 3

A group that contains a common ancestor but not all of its descendants. For example, reptiles – the ancestral amniote would be included but those descendants classified as mammals and birds are not. Paraphyletic groups are bad.

Question 4

What is a polyphyletic group?

Answer 4

A group that does not contain a common ancestor. For example, the supposed taxon Haemothermia – birds and mammals combined into one taxon on the basis of one character – warm bloodedness. Their common ancestor was an early amniote and was cold blooded; consequently, warm bloodedness arose polyphyletically. Polyphyletic groups are the work of the devil.

Question 5

Ingroup vs outgroup

Answer 5

A group actually being studied by the investigator – the clade whose members are being subjected to phylogenetic analysis.

vs.

Any group used in an analysis that is not included in the ingroup. Outgroups are used to assess the polarity of character state change in the ingroup.

Question 6

What are sister groups?

Answer 6

Two monophyletic groups who are their own closest relatives