Note: The lecture you just listened to provides one professor’s interpretation of evidence related to the evolution of whales. You might be interested to know that the evolution of whales is still being studied, and as new evidence becomes available, alternative inter-pretations may be more accurate.
Directions: Now answer the questions.
1. What is the lecture mainly about?
A. Recent fossil evidence connecting whales and the hippopotamus
B. Difficulties in determining the evolutionary history of whales
C. Similarities among ancient ancestors of whales
D. Similarities between whales and other modern-day animals
2. According to the professor, what three aspects of the Ambulocetus fossil make Ambulocetus a likely bridge between land mammals and sea mammals? Choose 3 answers.
A. It had an elongated skeletal structure.
B. It strongly resembled a modern hippopotamus.
C. It had an unusually long and thin tail for a whale.
D. It had limbs that could have been used for walking.
E. Its skull had ear bones characteristic of land mammals.
3. According to the professor, what does the discovery of Ambulocetus mean to researchers?
A. it fills a gap in the fossil evidence for whale evolution.
B. It has become less significant since the discovery of Basilosaurus.
C. It calls into doubt the theory that whales evolved from land mammals.
D. It suggests that whales evolved more recently than was previously believed.
4. What evidence suggests that whales are descendants of the hippopotamus?
A. Similarities between hippopotamus fossils and the Ambulocetus fossil
B. Similarities in the genes of hippopotamuses and whales
C. Similarities in the habitats of modern hippopotamuses and ancient whales
D. Similarities in the skeletal structures of modern hippopotamuses and ancient whales
5. What is the professor’s opinion about recent genetic studies relating to whale evolution?
A. They solve a long-standing mystery involving fossil evidence.
B. They contain significant errors.
C. They present evidence that conflicts with fossil evidence.
D. The findings of the various studies should not have surprised researchers.
6. What does DNA evidence indicate about relationships among whales?
A. All modern whales descend from sperm whales.
B. Differences among toothed whales are less significant that was previously thought.
D. Not all toothed whales are closely related.
E. Sperm whales are more closely related to killer whales than was previously thought.
Listen to part of a lecture in a marine biology class.
We know whales are mammals and that they evolved from land creatures. So the mystery is figuring out how they became ocean dwellers. Because, until recently, there was no fossil record of what we call “the missing link,” that is, evidence of species that show the transition between land-dwelling mammals and today’s whales.
Fortunately, some recent fossil discoveries have made the picture a little bit clearer. For example, a few years back, in Pakistan, they found the skull of a wolflike creature; it was about 50 million years old. Scientists’d seen this wolflike creature before, but this skull was different; the ear area of the skull had characteristics seen only in aquatic mammals, specifically whales. Uh, then—also in Pakistan—they found the fossil of another creature, which we call Ambulocetus batons.
That’s a mouthful, eh? The name Ambulocetus natans comes from Latin, of course, and means “walking whale that swims”; it clearly had four limbs that could have been used for walking. It also had a long, thin tail typical of mammals, something we don’t see in today’s whales. But: it also had a long skeletal structure, and that long skeletal structure suggests that it was aquatic…
And very recently, In Egypt, they found a skeleton of Basilosaurus.
Basilosaurus was a creature that we had already known about for over 100 years, and it has been linked to modern whales because of its long whalelike body, but this new fos-sil find showed a full set of leg bones, something we didn’t have before. The legs were too small to be useful—they weren’t even connected to its pelvis and couldn’t have sup-ported its weight—but it clearly shows Basilosaurus’ evolution from land creatures, so that’s a giant step in the right direction. Even better, it establishes Ambulocetus as a clear link between the wolflike creature and Basilosaurus.
Now, these discoveries don’t completely solve the mystery. I mean, Ambulocetus is a mammal that shows a sort of bridge between walking on land and swimming, but it also is very different from the whales we know today. So really, we are working with just a few pieces of a big puzzle.
Uh, a related debate involves some recent DNA studies. Remember, DNA is the genetic code for any organism, and when the DNA from two different species is similar, it sug-gests that those two species are related … And when we compared some whale DNA with DNA from some other species, we got quite a surprise: the DNA suggests that
whales are descendants of the hippopotamus!
Yes, the hippopotamus! Well, that came as a bit of a shock, I mean, that a four-legged land and river dweller could be the evolutionary source of a completely aquatic creature up to 25 times its size? Unfortunately, this revelation about the hippopotamus apparently contradicts the fossil record, which suggests that the hippopotamus is only a very distant relative of the whale, not an ancestor, and, of course, as I mentioned, that whales are descended not from hippos but from that distant wolflike creature. So we have contra-dictory evidence. And more research might just raise more questions and create more controversies. At any rate, we have a choice: we can believe the molecular data, the DNA, or we can believe the skeleton trail, but, unfortunately, probably not both …
Uh, and there have been some other interesting findings from DNA research: For a long time, we assumed that all whales that had teeth, including sperm whales and killer whales, were closely related to one another. And the same for the toothless whales, like the blue whale and other baleen whales—we assumed that they’d be closely related. But recent DNA studies suggest that that’s not the case at all; the sperm whale is actually closely related to the baleen whale, and it’s only distantly related to the toothed whales.
So that was a real surprise to all of us.
Note: The lecture above provides one professor’s interpretation of evidence related to the evolution of whales. You might be interested to know that the evolution of whales is still being studied, and as new evidence becomes available, alternative interpretations may be more accurate.