1. LON-CAPA Logo
  2. Help
  3. Log In
 

POSSIBLE ANSWERS TO HOMEWORK ASSIGNMENT # 2 VERTEBRATE ZOOLOGY

SPRING 2000 DR. CRONE

Topics: Cartilaginous fish, bony fish, and amphibians

  1. You're off sport fishing in the Caribbean, when there's a strong tug on your line. After a long fight, you haul in a fish you've never seen before. Before you use your knife to gut it, what types of external features would you look for to indicate that it's a cartilaginous and not a bony fish?

    2. The cartilaginous fish have many distinctive external features that help to distinguish them from other fish. In the overall shark outline, a rostrum or snout is prominent, accompanied by a ventrally-placed mouth. The snout is covered with small pores or organs of Lorenzini for the sensing of electrical fields from other organisms. Uncovered gill slits are visible in the pharyngeal region. At the posterior end, the tail is heterocercal, with the dorsal caudal fin larger than the ventral caudal fin. The placement and attachment of the paired pectoral and pelvic fins is also distinctive. The pairs of fins are set apart from each other with broad attachments that do not allow reverse swimming. Furthermore, the pelvic fins of male cartilaginous fish are partly modified into claspers for internal fertilization. Finally, the texture of shark skin is distinctive, as microscopic, backward aiming placoid scales make stroking from tail to hard rough on the hands. In summary, cartilaginous fish appear sufficiently different from other fish to be able to identify them on sight.

    (Sources: week 4 lecture notes and handout; text (7th ed.), Ch.27, pp. 588-590)

  2. The Pacific salmon has a definite impact on the economies of Washington, British Columbia, and Alaska. What is the life cycle of the salmon? What human impacts interfere with this pattern?

    3. The Pacific salmon is one of few anadromous fishes that live in both fresh and salt water sometime during its life cycle. The new hatchlings (so-called alevin stage) will mature to a smolt stage in freshwater before the migration downstream to the ocean. Several years of saltwater living will add bulk and sexual maturity to the salmon before it begins its migration back to spawn. Swimming upstream, the salmon will return to the stream of its birth before egg-laying, externally fertilizing, and dying. Human interventions have a dramatic effect on the number of salmon. Run-off pollution compromises the spawning grounds. Dams interfere with migration both upstream and downstream. High levels of ocean salmon fishing lead to greatly reduced numbers of adults returning to spawn. In summary, the involved life cycle of the salmon allows a variety of human impacts to lessen the number of Pacific salmon.

    (Sources: week 5 lecture notes and handout; text (7th ed.), Ch.27, pp. 599-601)

  3. A major feature of the amphibians and other tetrapods are limbs. What are the major limb bones off of both the pectoral and pelvic girdles? What are examples of fossil evidence in the evolution of limbs from fins? What were (presumably) major influences on this pattern of change?

The limbs of all tetrapods have consistent features, from a large anchoring bone to increasing numbers of bony elements from proximal to distal. As examples, the major bones of the tetrapod forelimb//hindlimb include the anchoring flat bone of the scapula//hip bone (respectively), the humerus//femur, the radius//tibia, the ulna//fibula, the carpals//tarsals, the metacarpals//metatarsals, and the phalanges in a proximal to distal ordering. These patterns appear to be ancient, as indicated by a series of fossils from the Devonian Period (400 to 360 million years ago). Eusphenopteran, a lobe-finned fish, Acanthostega, an amphibian with gills and limbs too weak to walk on, and Ichthyostega, a land-worthy amphibian with a large fish-like tail, all show modifications of these basic limb patterns. Presumably, environmental conditions selected for limbs and the ability to crawl onto land. Shallow water that occasionally dried up was the presumptive habitat of these organisms, with the shallowness providing protection against large predators. Shallow water warms more quickly than deep water, so that it is more prone to evaporation and carries less oxygen dissolved in it. As a result, the combination of limbs strong enough to travel on land, and lungs (modified swim bladders) to supplement gills would have been useful features in this setting. Given that the bones of the lobe-finned fish"worked" in this setting, it probably is not surprising that the basic limb bone plan is still seen today, even in human beings.

(Sources: week 6 lecture notes and handout; text (7th ed.), Ch.28, pp. 607-609)

|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|

Please send comments and questions to: cronewil@hvcc.edu

 

HVCC home page

Copyright 1999, 2000 by Wilson Crone

External and unofficial links are not endorsed by Hudson Valley Community College

This web page last updated on March 3, 2000