Comparative Anatomy Concepts

1
Comparative AnatomyConcepts Premises

• Note Set 1
• Chapters 1 2

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
3
Major Vertebrate Groups
Figure 2.2
4
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

5

• 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
• Ex Dog and gray wolf skull

Figure 2.4
6
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

7
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).
8
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

9

• Generalized- structure with broad function
• Ex human hand
• Specialized- structure with restricted function
• 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

10
Higher vs. Lower Vertebrates

• Amniotes- higher vertebrates with amniotic sac
• Ex reptiles, birds, mammals
• Anamniotes- lower vertebrates without amniotic
  sac
• Ex fish, amphibians
• Amnion- membrane sac that surrounds embryo
• Cleidoic egg- amniotic egg with shell

11

• Serial homology- serial repetition of body parts
  in single organism
• Ex Somites

Figure 2.7 Somite formation in 4 week old embryo.
12
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.
13
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

14

• Adaptive Radiation- diversification of species
  into different lines through adaptation to new
  ecological niches

Figure 2.9 Branching evolution increased
diversity.
15
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

16
Sea Squirt Sessile Adult
Figure 2.13 Adult sea squirt structures (see
book figure 3.4).
Figure 2.12 Adult sea squirt.

• Once larva attaches, notochord and nervous system
  disappear
• Resembles invertebrate

17
Literature Cited

• Figure 2.1- http//www.erin.utoronto.ca/w3bio356/
  lectures/early_amniote.html
• Figure 2.2- http//courses.lib.odu.edu/biology/kca
  rpent/less10nte.html
• Figure 2.3- Kardong, K. Vertebrates Comparative
  Anatomy, Function, Evolution. McGraw Hill, 2002.
  
• Figure 2.4- http//anthro.palomar.edu/animal/anima
  l_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/exhibi
  tions/lifecycle/12.asp
• Figure 2.8- http//www.edwardtbabinski.us/articles
  /snake_vestigial_limb.html
• Figure 2.9- http//anthro.palomar.edu/animal/anima
  l_1.htm
• Figure 2.10- http//www.umanitoba.ca/faculties/sci
  ence/biological_sciences/lab13/biolab13_3.html
• Figure 2.11- http//cas.bellarmine.edu/tietjen/ima
  ges/agnaths.htm
• Figure 2.12- http//www8.nos.noaa.gov/coris_glossa
  ry/index.aspx?lettera
• Figure 2.13- http//www.auburn.edu/academic/classe
  s/zy/0301/Topic3/Topic3.html