COMPARATIVE ANATOMY: DEFINITIONS, CONCEPTS, PREMISES Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City
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.
TELEOLOGY • Birds have wings in order that they may fly. • Implies a preconceived design or purpose of a supernatural intelligence
ORGANIC EVOLUTION • Birds have wings therefore they can fly. • Implies role of fortuitous genetic changes induced by natural laws governing behavior of matter.
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
EARLY NATURALISTS • Jean BaptisteLamarcke- 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
ONTOGENY RECAPITULATES PHYLOGENY Embryonic development vs.Evolutionary history of a taxon
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
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
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
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
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
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!
SYSTEMATICS vs TAXONOMY • Process vs. Conventions with which organisms are named and grouped • Traditional (Linnean) systematics- hierarchical arrangement forming binomial system of taxonomy • Phylogeneticsystematics- arrange organisms into groups based on a common ancestor and all of its descendants
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
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.
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
CLADISTICS TERMINOLOGIES • A nodecorresponds 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 taxonto each other.
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 outgrouptaxon. • The clade arising from node B includes all three ingrouptaxa.
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.
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
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
HIGHER and LOWER- relative position of major taxa on a phylogeneticscale 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
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