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Comparative Anatomy Concepts & Premises

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1 Comparative Anatomy Concepts & 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 (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 2.12: 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

17 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 Figure Figure Figure

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