Comparative anatomy concepts premises
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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.

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Comparative Anatomy Concepts & Premises

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Comparative AnatomyConcepts & Premises

Note Set 1

Chapters 1 & 2


  • 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


  • 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

      • Ex: Dog and gray wolf skull

Figure 2.4


  • Paedomorphosis- Ontogenetic changes where larval features of ancestor becomes morphological features of descendant

  • Juvenile character stage of ancestor is retained

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 (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

      • 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

  • 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

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

      • Ex: Somites

    Figure 2.7: Somite formation in 4 week old embryo.


    • 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.


    • 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-

    Figure 2.2-

    Figure 2.3- Kardong, K. Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, 2002.

    Figure 2.4-

    Figure 2.5-

    Figure 2.6- Morey, Darcy F. The Early Evolution of the Domestic Dog. American Scientist, Vol. 82, No. 4, p342.

    Figure 2.7-

    Figure 2.8-

    Figure 2.9-

    Figure 2.10-

    Figure 2.11-

    Figure 2.12-

    Figure 2.13-

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