L4 Speaking Task # 3

Opened: Thursday, 7 April 2016, 1:00 AM
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L4 Speaking Task # 3

Directions: (read first)

  1. Begin by reading the passage in the box below. Do not exceed 45 seconds. You can use the clock on the right to time yourself.

  2. Next listen to a lecture about the topic in the passage by clicking the start button in the recording section below. You may take notes as you listen.

  3. Then record your response by clicking the "Add Submission" button at the bottom of the page.

  4. If you get a Flash permission message, check "Allow" and "Close".

  5. Next, click the "Record" button and begin speaking. You will have 60 seconds for your response. You may need to click "Stop" when you have finished.

  6. Finally, click the "Save Changes" button at the bottom to upload your recording for grading and teacher comments.

When you are ready, put on your headset and click the start button on the audio player here to begin this speaking task.

The History of Sharks

The earliest known sharks date from more than 420 million years ago. Since that time, sharks have diversified into over 400 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 ft).

Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark that can survive in both seawater and freshwater. They breathe through five to seven gill slits.

Evidence for the existence of sharks dates from the Ordovician period, over 450–420 million years ago, before land vertebrates existed and before many plants had colonized the continents. Only scales have been recovered from the first sharks and not all paleontologists agree that these are from true sharks. The oldest generally accepted shark scales are from about 420 million years ago, in the Silurian period.

The first sharks looked very different from modern sharks. The majority of modern sharks can be traced back to around 100 million years ago. Most fossils are of teeth, often in large numbers. Partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils.

Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark are apex predators—organisms at the top of their underwater food chain. Their predatory skill fascinates and frightens humans, even though their survival is threatened by human-related activities.