1. Mrs. Ofelia Solano Saludar
COMPARATIVE ANATOMY: DEFINITIONS, CONCEPTS, PREMISES
Mrs. Ofelia Solano Saludar
Department of Natural Sciences
University of St. La Salle
Bacolod City

2. COMPARATIVE ANATOMY
Includes both descriptive and functional vertebrate morphology
Deals with patterns of similarity in terms of common structure, function and development, and the process that gave rise to this pattern.

3. TELEOLOGY Birds have wings in order that they may fly.
Implies a preconceived design or purpose of a supernatural intelligence

4. ORGANIC EVOLUTION Birds have wings therefore they can fly.
Implies role of fortuitous genetic changes induced by natural laws governing behavior of matter.

5. MUTABILITY vs. IMMUTABILITY OF THE SPECIES
Theory of Mutability- organisms are changing, and those here today are descendants of those that were here earlier
Theory of Immutability- de novo appearance of the species

6. EARLY NATURALISTS
Jean Baptiste Lamarcke- characteristics acquired through use and disuse of morphological characteristics are heritable
Charles Darwin and Alfred Wallace - individual variations are due to selection processes
da Vinci, Vesalius, Galen- Italian artists began anatomical observations
Georges Cuvier- French naturalist, founder of comparative anatomy and paleontology

7. Embryonic development vs. Evolutionary history of a taxon
ONTOGENY RECAPITULATES PHYLOGENY
Embryonic development vs. Evolutionary history of a taxon

8. Von BAER’S LAW- features common to all members of a major taxon develop earlier in ontogeny than do features that distinguish them from subdivisions of the group, e.g. notochord, dorsal nerve cord of chordates vs. skin, feathers of related groups
BIOGENETIC LAW- features that develop earliest in ontogeny are the oldest phylogenetically, having been inherited from early common ancestors
EVOLUTION- random chance mutations, coupled with geographic isolation leads to change in gene frequency in a population

9. HOMOLOGY- similarity of structure based from a common ancestor, e. g
HOMOLOGY- similarity of structure based from a common ancestor, e.g., stapes of mammalian middle ear and hyomandibular cartilage of sharks
SERIAL HOMOLOGY- segmental equivalence in metameric structures, however individual components may not be homologous, e.g., spinal nerves, vertebrae, muscles
HOMOPLASY (homoplastic structures)- all other similarities not derived from common ancestry, e.g., wings of butterfly and bird
ANALOGY- coincidental resemblance, e.g. flippers of a seal and fins of a fish

11. HOMOPLASY
ADAPTATION- hereditary modification of a phenotype with survival value, e.g. fish-like ichthyosaur, heterocercal and homocercal tails of fishes
EVOLUTIONARY CONVERGENCE- not closely related; dissimilar features evolved to become similar features based on environmental adaptations, e.g., webbed feet of frog, duck and platypus
PARALLEL EVOLUTION- related & isolated; corresponding features undergo equivalent changes in isolated environments

12. DIVERGENCE/ ADAPTIVE RADIATION- species evolved from common ancestor; morphological differences due to change in environment, e.g. streamlined bodies of sharks vs, flattened bodies of skates and rays

14. SPECIATION- isolation of a population from others of the same species; chance mutations, gene recombinations and genetic drift result to genetic incompatibilities
HETEROCHRONY- changes representing differences in timing or rate of developmental events, e.g. incomplete metamorphosis/ larval retention of urodeles
Paedogenesis- gonads develop quickly
Paedomorphosis immature features of ancestor become features of future SPECIES
Neoteny- immature features are retained as an adult in the INDIVIDUAL

15. If evolution had slowed the rate of shape change of a salamander, but kept everything else the same, we would have ended up with the axolotl!

16. SYSTEMATICS vs TAXONOMY
Process vs. Conventions with which organisms are named and grouped
Traditional (Linnean) systematics- hierarchical arrangement forming binomial system of taxonomy
Phylogenetic systematics- arrange organisms into groups based on a common ancestor and all of its descendants

17. PHYLOGENETIC SYSTEMATICS
Monophyletic- includes a common ancestor and all its descendants)
Paraphyletic- includes a common ancestor, but 1 or more descendants is omitted
Polyphyletic- no immediate common ancestor is shared

18. CLADISTICS
The method begins by grouping organisms based on a characteristic displayed by all the members of the group.
The larger group, or clade, will contain increasingly smaller groups (clades) that share the traits of the clades before them, but also exhibit distinct changes as the organism evolves.
To make a cladogram, scientists first collect data on the features of all the organisms they hope to classify.
This data is then analyzed to determine which characteristics were present in what could have been a common ancestor and which might have been developed in later times.

19. ANALYSIS OF DATA Characteristics: no (0), yes (1) 1 is eukaryotic
2 is multicellular
has segmented body
has jaws
has limbs
has hair
has placenta

20. EXAMPLE OF A CLADOGRAM

21. CLADISTICS TERMINOLOGIES
A node corresponds to a hypothetical ancestor.
A terminal node is the hypothetical last common ancestral interbreeding population of the taxon labeled at a tip of the cladogram.
An internal node is the hypothetical last common ancestral population that speciated (i.e., split) to give rise to two or more daughter taxa, which are thus sister taxon to each other.

22. Each internal node is also at the base of a clade, which includes the common ancestral population (node) plus all its descendents.
There are four terminal nodes in this example. These include members of the ingroup: Taxon 1, Taxon 2, and Taxon 3, and a single outgroup taxon.
The clade arising from node B includes all three ingroup taxa.

23. The “snip rule” determines which groupings of terminal nodes are clades, in a particular cladogram.
Whenever you "snip" a branch directly beneath an internal node, a clade falls off.
In the example, a grouping of Taxon 1 and Taxon 2 without Taxon 3 is not a clade, because there is no way to snip off the first two without Taxon 3 also falling off.

24. INGROUP- groups of interest in a clade
OUTGROUP- any group outside the clade of interest
SISTER GROUP immediate outgroup that shares a common ancestor with the ingroup
CROWN GROUP- includes all living members of a clade and its immediate ancestor
BASAL GROUP- lineages that diverge at a point close to the common ancestor within a clade
STEM GROUP- basal taxa not included in the crown group

25. A CASE OF SEMANTICS
PRIMITIVE- trait appears in an ancestor from which arose species retaining the trait, e.g. notochord
GENERALIZED- state of potential adaptability, e.g., mammalian hand evolved into bat’s wings, seals’ flipper
SPECIALIZED- represents an adaptive modification; e.g., beaks and claws of birds
DERIVED OR MODIFIED- state of change from an ancestral condition, e.g., loss of potential to form bone results to cartilaginous skeleton

26. HIGHER and LOWER- relative position of major taxa on a phylogenetic scale
SIMPLE- lack of complexity; however a simple skull is not primitive nor a primitive skull simple
ADVANCED and DEGENERATE- directional modification; employs value-judgment from its connotation of progression
VESTIGIAL- phylogenetic remnant that was better developed in the ancestor, e.g., avian yolk sac
RUDIMENTARY- underdeveloped structure such as the pelvic girdles of whales, or the male Mullerian ducts

27. QUESTIONS?

28. next...
The Protochordates