Answers-1, BIO 3220, Introduction to Comparative Anatomy and the Vertebrates


1. Define comparative vertebrate anatomy, morphology, phylogeny, embryology.
Anatomy – description and observation of structures
Morphology – relating and interpreting structures
Phylogeny – evolutionary history of a group or structure
Embryology – study of development of structures in embryos

2. Contrast homology and analogy. Give an example of homoplasty.
Homology – shared common ancestry; related
Analogy – shared common function
Homoplasty – shared anatomy, but not homologous; for example, the wing of a bird and the wing of a grasshopper

3. Discuss adaptation and preadaptation. Briefly discuss Darwin’s theory of natural selection.
Adaptation – function first, then form; for example, there was food on land, so a fish with “funny fins” crawled to it
Preadaptation – form first, then function; for example, fish with “funny fins” had fins first and came to land
Theory of natural selection – natural selection is often described as “survival of the fittest;” it maintains that the organisms best suited to survive in their environment are more likely to reproduce and pass their genetic material to the next generation, while those with less advantageous traits are less likely to survive long enough to reproduce

4. Compare and contrast divergent, convergent, parallel and organic evolution.
Divergent – the evolutionary pattern in which two related species gradually become increasingly different; often occurs when closely related species diversify to new habitats
Convergent – the pattern that takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure; for example, whales and fish have some similar characteristics since both had to evolve methods of moving through the same medium, water
Parallel – the pattern that occurs when two species evolve independently of each other, maintaining the same level of similarity; usually occurs between species that do not occupy the same or similar niches in a given habitat
Organic – a concept that embodies the belief that existing animals and plants developed by a process of gradual, continuous change from previously existing forms

5. What is a vestigial structure? A rudimentary structure?
Vestigial – structures better developed in ancestors
Rudimentary – structures better developed in descendents

6. Define ontogeny.
Ontogeny – an individual’s life history from fertilization to death

7. Describe heterochrony – specifically paedogenesis, neoteny, and paedomorphosis.
Heterochrony – changes in relative rates of development
Paedogenesis – gonads develop fast
Paedomorphosis – immature features of ancestor become characteristics of future species; for example, the gills of mudpuppies
Neoteny – type of paedomorphosis in which larval features are retained in the individual

1. Review the vertebrate taxonomy from your zoology course.

2. Name four main chordate features.
Dorsal hollow nerve cord, notocord, pharyngeal gill slits/arches, postanal tail

3. Theorize the origin of the vertebrates.
Through comparative embryology, scientists now believe that the chordates arose from a primitive sessile-benthic arm-feeding echinoderm. Tunicates are small marine invertebrate chordates quite common today; they may hold the key to vertebrate origins. Tunicates have a sessile adult stage in which they are filter-feeders with gill slits but no notochord or dorsal nerve tube. Tunicate larvae, though, are free-swimming filter-feeders; they are characterized by a notochord and dorsal nerve tube lost later when they metamorphose into sessile adults. It is possible that a tunicate-like organism evolved by way of neoteny into a free-swimming adult chordate. In this case, the juvenile features of tunicate-like organisms (notochord, dorsal nerve tube, and swimming ability) may have been evolutionarily retained in the succeeding chordates. The lancelet is a chordate with a free-swimming adult stage, and also a filter-feeding bottom-dweller. We may predict, then, that the first vertebrates were free-swimming, bottom-dwelling filter feeders, probably during the Ordovician Period, 500 million years ago.

4. Discuss vertebrate characteristics.
Vertebral column – bone or cartilaginous vertebrae
Bilateral symmetry – characteristic features on both sides
Ventral chambered heart – “closed” heart
Closed circulatory system – blood in heart or tubes; for example, veins and arteries
Complete digestive tract – from mouth to anus
Cephalization – sensory/nerve structures on “head” end

5. Review Vertebrate Classification Handout.

6. Define tetrapod, fish, agnathostome, and gnathostome.
Tetrapod – four-limbed animal
Fish – any of numerous cold-blooded aquatic vertebrates, characteristically having fins, gills, and a streamlined body and including specifically any of the Osteichthyes, having a bony skeleton and any of the class Chondrichthyes, having a cartilaginous skeleton and including the sharks, rays, and skates; any of various primitive aquatic vertebrates of Cyclostomata, lacking jaws and including the lampreys and hagfishes.
Agnathosotme – jawless vertebrates
Gnathostome – jawed vertebrates

7. Define and give an example of endothermic/homeothermic and ectothermic/poikilothermic animals.
Endothermic – generate own heat
Homeothermic – maintain steady temperature
Example – mammals, birds
Ectothermic – heat from environment
Poikilothermic – temperature varies
Example – snakes, fish

8. Examine the relative time periods of vertebrate classes; i.e. when did they originate/dominate. Review Geologic Period Handout.

9. What is an amniote and anamniote?
Amniote – an animal whose eggs contain an amnion, a membrane that surrounds the embryo and helps retain fluids and cushions embryo
Anamniote – an animal whose eggs lacking embryonic membranes or amnion