Comparative Anatomy
Concepts & Premises
Note Set 1
Chapters 1 & 2
Phylogeny



Historical relationship
between organisms or
lineages
Ancestry shown by
phylogenetic tree
Phylogenetic
Systematics- shows
relationships from past
to present

Shows evolutionary
relationships
Figure 2.1
Major Vertebrate Groups
Figure 2.2
Cladistics


Method for studying
phylogeny
Shows ancestry of
derived features
Figure 2.3


Advanced structures are derived, synapomorphic
Primitive structures are not derived, ancestral,
symplesiomorphic

Convergence- organism response to similar
environment

Similar structures yet distantly related organisms


Ex: limbs of fishes and marine mammals
Parallelism- structure similarities in closely related
organisms

Similar morphology due to parallel evolution

Figure 2.4
Ex: Dog and gray wolf skull
Paedomorphosis
Figure 2.5 - (Left) larval state salamander with external, feathery gills; (Center) adult
salamander that lost gills; (Right) adult axolotl salamander retains juvenile external gills.


Paedomorphosis- Ontogenetic changes where
larval features of ancestor becomes morphological
features of descendant
Juvenile character stage of ancestor is retained
Paedomorphosis (cont.)
Figure 2.6: Natural selection pressures on the wolf may have lead to the formation of a new
species, the domestic dog. The prehistoric adult dog skull (center) can be compared to the
adult wolf skull (left) and particularly the juvenile wolf skull (right).
Paedomorphosis (cont.)



Neoteny- delayed rate of somatic development
Progenesis- precocious sexual maturation in
morphological juvenile
Behavioral Paedomorphology- juvenile
behavioral stage retained


Ex: wolf pup and domestic dog
Heterochrony- change in rates of character
development during phylogeny

Generalized- structure with broad function


Specialized- structure with restricted function



Ex: human hand
Ex: single digit hand
Modification- change from previous state, may
be preadaptive
Preadaptation- current trait that will be useful in
future

Ex: binocular vision and thumb
Higher vs. Lower Vertebrates

Amniotes- higher vertebrates with amniotic sac


Anamniotes- lower vertebrates without amniotic
sac


Ex: reptiles, birds, mammals
Ex: fish, amphibians
Amnion- membrane sac that surrounds embryo

Cleidoic egg- amniotic egg with shell

Serial homology- serial repetition of body parts
in single organism

Ex: Somites
Figure 2.7: Somite formation
in 4 week old embryo.
Vestigial

Vestigial- phylogenetic remnant that was better
developed in ancestor.
(e.g., human appendix, fruit fly wings,
python leg spurs)
Figure 2.8: Ball python spurs.
Rudimentary

Phylogenetic sense- structure is fully exploited by a
descendant


Ex: rudimentary lagena in fish (sac of semicircular canals) develops
into organ of Corti in mammals
Ontogenetic sense- structure is underdeveloped or not
fully developed from embryo to adult


Ex: Muellerian tract in females develops into reproductive tract; yet
in males, duct is rudimentary
Ex: Woffian duct in males develops into sperm duct; yet in females,
duct is rudimentary
Adaptive
Radiation- diversification of species
into different lines through adaptation to new
ecological niches
Figure 2.9: Branching evolution; increased diversity.
Sea Squirt
Free Swimming Larva
Figure 2.10: Larval form of sea squirt.

Figure 2.11: Lamprey larval structures.
Larval stage of sea squirt resembles vertebrate
tadpole
Developed notochord and dorsal nerve cord
 Rudimentary brain and sense organs

Sea Squirt
Sessile Adult
Figure 2.12: Adult sea squirt.

Figure 2.13: Adult sea squirt
structures (see book figure 3.4).
Once larva attaches, notochord and nervous
system disappear

Resembles invertebrate
Literature Cited
Figure 2.1- http://www.erin.utoronto.ca/~w3bio356/lectures/early_amniote.html
Figure 2.2- http://courses.lib.odu.edu/biology/kcarpent/less10nte.html
Figure 2.3- Kardong, K. Vertebrates: Comparative Anatomy, Function, Evolution.
McGraw Hill, 2002.
Figure 2.4- http://anthro.palomar.edu/animal/animal_2.htm
Figure 2.5- http://evolution.berkeley.edu/evosite/evo101/IIIC6dDevochange2.shtml
Figure 2.6- Morey, Darcy F. The Early Evolution of the Domestic Dog. American
Scientist, Vol. 82, No. 4, p342.
Figure 2.7- http://www.sciencemuseum.org.uk/exhibitions/lifecycle/12.asp
Figure 2.8- http://www.edwardtbabinski.us/articles/snake_vestigial_limb.html
Figure 2.9- http://anthro.palomar.edu/animal/animal_1.htm
Figure 2.10http://www.umanitoba.ca/faculties/science/biological_sciences/lab13/biolab13_3.ht
ml
Figure 2.11- http://cas.bellarmine.edu/tietjen/images/agnaths.htm
Figure 2.12- http://www8.nos.noaa.gov/coris_glossary/index.aspx?letter=a
Figure 2.13- http://www.auburn.edu/academic/classes/zy/0301/Topic3/Topic3.html