Introduction

Updated 17 January 2005

DEFINE Vertebrate Morphology

A. Morphology - form, structure (external and internal); descriptive and analytical (cf anatomy; course = comparative anatomy) - vertebrate morphology seeks to explain vertebrate design by elucidating the reasons for and processes that produce the basic structural plan of an organism; interested in both what and why

Define Vertebrate

A. Phylum Chordata (defined by specific body plan): slide 1

1. Dorsal hollow nerve cord

2. Notochord

3. Coelom (tube-within-a-tube); visceral vs. somatic

4. Pharyngeal arches/slits

5. Postanal tail

B. Subphylum Vertebrata: define by vertebrae (various degrees of development); non-vertebrate chordates

C. Recent vertebrates (7 major groups), brief survey – slide 2

Approach

A. Survey structure by organ system (n=10)

B. Objectives

a. Learn basic descriptive vertebrate structure; spend much time observing and memorizing

b. Comparative approach (vertebrates diverse; look for patterns, interpretation); must apply principles (especially phylogeny)

C. Subject matter is highly visually oriented; must spend time studying both specimens and figures (both text and online). To learn vertebrate morphology, you must have a visual image in your mind of the structures being discussed.

Evolution - major process of vertebrate morphology; must understand framework from which vertebrate morphology is understood (cf world religions course)

A. Distinguish three major facets of evolution

1. Fact of evolution (it has occurred; evidence ranges from molecular-fossil record)

2. Mechanism of evolution (microevolution, directly demonstrable)

3. Course of evolution (scientifically controversial primarily because of the problems associated with piecing together historical events with very little evidence)

B. Course of evolution may cause problems with faith

1. How do you harmonize evolutionary thinking with faith?

2. Important to distinguish between evolution (scientific theory) and evolutionism (philosophical extension)

3. In this course, “evolution” always refers to the scientific theory

C. Important evolutionary concepts and terms

1. Evolution is limited and opportunistic; works with existing raw material in a given environment

2. The benefits of a distant future do not drive evolutionary change (cannot anticipate tomorrow); the only things that shape animal design are the immediate demands of the current environment (opportunistic; suboptimal design)

3. How well adapted a species is only makes sense in context of its niche; continual improvement only in a constant environment

4. Species (basic unit) - A group of interbreeding individuals on a common evolutionary trajectory

5. Speciation - dividing of one species into two different species due to:

a. changing allele frequencies in populations of a species due to violations of any of the assumptions of H-W Equilibrium

b. changing genetic composition of the species due to polyploidy, chromosome rearrangement, etc.

6. Phylogeny - history of descent of a group of taxa (such as species) from their common ancestors, including the order of branching and sometimes absolute ages of divergence (hypothetical e.g., slides 3-5)

-importance of phylogenies:

a. explains how the diversity of life present today could have diverged from a few common ancestors

b. provides a basis for organizing life currently present on earth (taxonomic classification)

c. provides a basis for predicting patterns that should be found among extant organisms

d. provides a basis for making predictions about what we should see in the fossil record

7. View course of evolution as a 3-D branching bush where at any level all organisms are adapted to their specific environments; vs. scale of nature concept (2D ladder of progress - a commonly mistaken view of how evolution is thought to work)

8. Terms

a. homologous (structures with similar embryonic origins, e.g., notochord); reflects common ancestry

b. analogous (structures with similar functions, e.g., egg teeth of lizard/snake, crocodilian); reflects functional convergence

1) structures may be: analogous and homologous, analogous but not homologous, homologous but not analogous (e.g., lizard tongues), neither analogous nor homologous

2) how determine homology? - similarity in position to other structures (e.g., muscle inervation in bird wing), developmental history (embryology)

b. primitive (ancestral) vs. advanced (derived) - re origin

c. generalized vs. specialized - relative breadth of function; e.g., feeding

d. clade (=phylogenetic line or lineage); ancestral group and all its descendents; monophyletic

e. grade (adaptive level reached by a group); can be monophyletic or polyphyletic (unatural group)

f. paraphyletic (ancestral group and some of its descendents); e.g., Class Reptilia

Phylogeny and taxonomic classification

1. Assumption - similarity of structure reflects similarity of evolutionary history

2. Evolutionary problems

a. convergence - similarity of unrelated forms (e.g., moloch)

b. adaptive radiation - dissimilarity of related forms (e.g., Darwin's finches)

3. Taxonomic characters - not all structures have equal weight in classification; use conservative derived characteristics (e.g., hair, mammary gland define mammals)

4. Methodological problems

a. traditional (Linnaean) taxonomy (phenetics) - often does not reflect evolutionary history (artificial); governed by the International Code of Zoological Nomenclature (ICZN); concept used for the last 250 years

b. proposed taxonomy (phylogenetic systematics/cladistics – What is Cladistics?) – better reflects evolutionary history (governed by the proposed Phylocode)

5. Classification examples

a. Linnaean – Kardong, Appendix D, part 1

b. Cladistic – Kardong, Appendix D, part 2

6. Phylogenetic vs. traditional classification (Pough et al. 2002, slide 6)

Phylogenetic patterns of life on earth (historical)

A. Most phyletic lines appear/disappear suddenly in fossil record

1. Slow start, flourish, decline; most (>90%) spp extinct

2. Few intermediates, gaps; if continuum, how classify? e.g., ruler (colubrids)

B. Why gaps? (difficult question) If assume that the greatest evolutionary change comes with strong selection pressures (often concurrent with unstable/harsh environments):

1. Rapid change leaves relatively few fossils (temporal and small population size)

2. Disrupted fossilization sites (fewer fossils)

3. Special creation (“kinds” = taxa, not necessarily species); attributed to God but ignores the “how”