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POSSIBLE ANSWERS FOR HOMEWORK ASSIGNMENT # 1

VERTEBRATE ZOOLOGY SPRING 2000 DR. CRONE

Topics: Introduction to Animals and Chordates

These possible answers are on reserve at the library, the Biology Study Center, AMZ 219, and my web site. You may want to review Homework # 1 for the first lecture exam.

  1. In the laboratory portion of Vertebrate Zoology, which of the following approaches will be the most appropriate for dissection: anterior, posterior, dorsal, or ventral? Discuss in terms of your understanding of overall vertebrate structure.

    2. Anterior represents the head, posterior the tail, dorsal the back, and ventral the belly aspects of animal orientation. A major goal of dissection is to see the relationship of internal organs clearly. A ventral approach to vertebrate dissection will accompany this most easily, by not having to cut through or around the spine.

    (Resources: Week 1 lecture notes and lecture handout; lab manual--check any vertebrate dissection!; text [7th ed.], Fig. 27-13, p. 592, Fig. 29-5, p. 627)

  2. What are the four distinctive structural features of the phylum Chordata found during some part of the life cycle of any chordate? Where are they found in the life cycle of a sea squirt? Where are they found in the life cycle of a lancelet? Please be as specific as you can.

The"four favorite phylum features" of the chordates are:

  1. notochord (internal dorsal stiffening rod)
  2. dorsal, hollow nerve cord (dorsal to the notochord and usually enlarged anteriorly as a brain)
  3. postanal tail
  4. pharyngeal slits/pouches (in the neck region)

To be a member of Phylum Chordata, these four features have to be present at some time during the life cycle. A sea squirt (tunicate) of the Subphylum Urochordata has all four features only in its short-lived larval form. After a dramatic metamorphosis, the adult sea squirt has only the pharyngeal slits modified into a large filter feeding structure as a key feature. The other three structures are not visible in the adult (or in the case of the nerve cord, have degenerated to a large ganglion or nerve cell cluster). In contrast, the larval lancelet (amphioxus) of Subphylum Cephalochordata is similar to the adult. Throughout its life cycle, the lancelet shows clearly these four features.

(Resources: Week 2 lecture notes and lecture handout; text [7th ed.], Ch. 26, pp. 569-573)

  1. An important part of the course is developing a sense of time scale when different events occurred in the evolution of the vertebrates. This question, based on material you saw in the video,"Eyewitness: Dinosaur," will help to reinforce that sense of time. During what geologic periods did the dinosaurs live--name them and give them approximate dates. What were conditions like back then (in each of these periods)? What other major forms of life (vertebrate or otherwise) were appearing in the fossil record at that time? You may find that other sources (document if you are using them) will have this more laid out than the 7th edition of the Hickman et al. text. I want you to know enough about geologic history so that when I mention periods in lecture, they'll make sense to you.

The dinosaurs were the dominant land vertebrates of the Mesozoic Era and its included Triassic (250 to 180 million years ago), Jurassic (180 to 150 million years ago), and Cretaceous (150 to 65 million years ago) Periods. Geologically, the Triassic and Jurassic periods were dominated by Pangaea, where the land continents as we know them were fused together into one large land mass. Pangaea began to break up during the Cretaceous Periods into the continental patterns we are more familiar with. The major plant life of the periods varied as well. The Triassic Period was a time of steamy jungle of fern and fern ally plants. The Jurassic Period was also humid and moist, but with conifer-type plants predominating. The Cretaceous Period was more a period of flowering plants, while cycads and relatives still remained. The other major land-dwelling vertebrate groups derived from the reptiles, the birds and the mammals, also made their first appearance in the fossil record during the Mesozoic Era.

(Resources: Study guide to"Eyewitness: Dinosaur; text [7th ed.], Ch. 29, pp. 623, 630-631; AG Collins et al., UCMP Web Time Machine, http://www.ucmp.berkeley.edu/help/timeform.html, accessed 1/13/00)

 

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

 

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This web page last updated on February 3, 2000