1. Lecture 14: Reconstructing Phylogenies
1) homoplasy (analogy) : character not present in RCA
- convergent evolution
- parallel evolution
2) homology : character inherited from CA
a) ancestral (symplesiomorphy)
- little change from distant ancestor
b) derived (synapomorphy)
- recent change
Start with some terminology

2. Homology vs. Analogy Same fundamental structure
Same relationship to surrounding characters
Similarities in embryology
humerus
radius
ulna
carpals
phalanges
Human, dog, whale, bat.

3. Embryology Haeckel’s (1886) biogenetic “law” :
“ontogeny recapitulates phylogeny”
each embryonic stage = adult stage
of ancestor
WRONG!
Von Baer’s (1828) law:
among related spp., early stages are more similar than later stages
examination of early dev’t can reveal close relationships
What are these examples??

4. Examples Successive stages of vertebrate embryos: Cattle: metacarpals
fish
                                                                      
chicken
pig
human
Cattle: metacarpals
start off separate; fuse
during development
Anteaters: teeth present early in development; resorbed

5. Von Baer’s Law
Sometimes useful to distinguish b/w ancestral & derived traits, not always:
e.g. fused cannon bone – derived
toothlessness in Edentates – derived
But, early stages may be special adaptations
- “beak” of tadpole
- milk teeth of bats
- cotyledons in plants
What do tadpoles use their beaks for?? Scrape food off rocks to filter
Milk teeth are for? Because jaw too small
Cotyledons are for? Contains food for early growth until seedling established

6. terminal stages of ancestor’s ontogeny may be lost
e.g. paedomorphosis:
(retention of juvenile characters in adult)
- in salamanders is derived, not ancestral

7. Reconstruction continues…
distinguish homologies from analogies
distinguish ancestral homologies from derived homologies
- need to determine polarity of change (ancestral → recent)

8. Strategies to Distinguish b/w Ancestral & Derived
1) morphocline or transformation series:
e.g. chromosome inversions in Drosophila
ABCDEFG ↔ AEDCBFG ↔ AEDFBCG
- can infer sequence, but which is ancestral?
a ↔ b

9. Outgroup Analysis
outgroup = taxon that diverged from a group before they diverged from each other
principle of parsimony: fewest changes
consider: 3 spp + outgroup sp.
- 1 character, 2 states
sp. 1 : b
sp. 2 : b
sp. 3 : a
sp. O: a
A B C D
Continued on next page…

10. the character state present in the outgroup is assumed to be ancestral
2 hypotheses: 1 : a → b (a = ancestral; b derived) : b → a (b = ancestral; a derived) O b a
b → a
a → b
vs.
the character state present in the outgroup is
assumed to be ancestral

11. Butterflies brush-footed, monarchs → 2 reduced legs
swallowtails, sulphurs → 6 functional legs
which state is ancestral ?
Moths diverged from butterflies before they diverged from each other (moths = outgroup)
moths → 6 functional legs
most parsimonious : 6 functional legs = ancestral

12. 5 Characters Character 1: shared by A, B, C (synapomorphy)
separates them from
outgroup
Synapomorphy – shared derived character.

13. Character 2:
unique derived trait in taxon B
no info about relationships
Character 3:
unique derived trait in taxon C

14. Character 4:
synapomorphy
unites B & C
Character 5:
unique derived trait in taxon A
no info

15. Fused cannon bones in cattle;
Toothlessness in adult anteaters:
Derived traits b/c:
unfused metacarpals & adult teeth are widespread in other mammals

16. Primitive characters
primitive condition in an ingroup is that which is found in outgroups
Common characters are not necessarily primitive!
Often true: owl monkeys are only nocturnal
primate; nocturnal habit is derived
However…

17. Primitive vs. Derived
Few vertebrates lack jaws, but jawlessness in lampreys is primitive, not derived
Distribution, not number of spp. with the trait, is important

18. Complete Fossil Record
Can aid in analysis
e.g. Progressive reduction in # of digits in horses
one-toed condition is derived
same info from outgroup analysis : rhinos & tapirs
But…

19. Litopterna Extinct horse-like mammals: 3 – toed observed later than
Outgroup analysis necessary
In fact, more detailed fossil record shows
3 – toed both before & after 1 – toed