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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

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


  • 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
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 cont1
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
    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

  • Figure 2.7: Somite formation in 4 week old embryo.

    Vestigial organism

    • 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 organism

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

    Figure 2.9: Branching evolution; increased diversity.

    Sea squirt free swimming larva
    Sea Squirt organismFree 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
    Sea Squirt organismSessile 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
    Literature Cited organism

    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-