TOPIC 2

PHYLOGENY & CLASSIFICATION

I. SYNTHETIC CLASSIFICATION

II. PHENETIC CLASSIFICATION

III. CLADISTIC CLASSIFICATION

A. CLADISTIC TERMINOLOGY

B. CONSTRUCTING A CLADOGRAM

 

HOW DO THE 3 SYSTEMS OF CLASSIFICATION DIFFER?

I. SYNTHETIC OR EVOLUTIONARY SYSTEMATICS

A. USES HOMOLOGOUS CHARACTERS IN DEFINING TAXA

B. USES BOTH ANCESTORAL & DERIVED CHARACTERS IN DEFINING TAXA

C. WEIGHS CHARACTERS IN DEFINING TAXA

( = SUBJECTIVE)

CONCEPT OF "ADAPTIVE ZONE"

 

II. PHENETICS OR NUMERICAL TAXONOMY

A. USES OVERALL SIMILARITY IN DEFINING TAXA & CONSTRUCTING TREES

B. INCORPORATES AS MANY CHARACTERS AS POSSIBLE IN CONSTRUCTING TREES

C. DOES NOT DISTINGUISH BETWEEN HOMOLOGOUS & ANALAGOUS CHARACTERS IN DEFINING TAXA

= ALL CHARACTERS ARE OF EQUAL VALUE

(= OBJECTIVE)

 

III. CLADISTIC OR PHYLOGENETIC SYSTEMATICS

A. CLASSIFIES ORGANISMS BASED ON THE ORDER INTIME THAT BRANCHES DIVERGED ALONG A DICHOTOMOUS PHYLOGENETIC TREE

= A CLADOGRAM

B. USES ONLY "SHARED DERIVED CHARACTERS" (= NOVEL HOMOLOGIES = SYNAPOMORPHIES) IN DEFINING TAXA & CONSTRUCTING TREES

 

C. DEGREE OF DIVERGENCE IS NOT IMPORTANT IN DEFINING TAXA= ALL "SHARED DERIVED CHARACTERS" ARE OF EQUAL VALUE

(= OBJECTIVE)

D. RECOGNIZES (= NAMES) MONOPHYLETIC TAXA ONLY

REJECTS:

POLYPHYLETIC TAXA

PARAPHYLETIC TAXA

 

CLADISTIC TERMINOLOGY

CLADE = EVOLUTIONARY BRANCH

APOMORPHY = DERIVED CHARACTER

SYNAPOMORPHY = SHARED DERIVED (NEW) CHARACTER

PLEISOMORPHY = ANCESTORAL (PRIMITIVE) CHARACTER

OUTGROUP = A TAXON THAT IS RELATED TO THE GROUP UNDER STUDY, BUT NOT AS CLOSELY RELATED AS GROUP MEMBERS ARE TO EACH OTHER

(USED TO RECOGNIZE ANCESTORAL CHARACTERS)

PARSIMONY = ACCEPTANCE OF THE SIMPLEST (THUS MOST PROBABLE) EXPLANATION FOR AN OBSERVED PATTERN

MONOPHYLY

1. A TAXON CONTAINS ALL DESCENDENTS OF A COMMON ANCESTOR

2. A TAXON CONTAINS ONLY DESCENDENTS OF THAT COMMON ANCESTOR

3. A TAXON CONTAINS THE COMMON ANCESTOR ITSELF

PARAPHYLY

A TAXON INCLUDES SOME DESCENDENTS OF A BASAL COMMON ANCESTOR & EXCLUDES OTHER DESCENDENTS

POLYPHYLY

A TAXON INCLUDES MEMBERS DESCENDED FROM 2 DIFFERENT IMMEDIATE ANCESTORS