雅思阅读 096: The Cretaceous Kraken — Giant Octopuses of the Deep

Adapted from 'Kraken fossils show enormous, intelligent octopuses were top predators in Cretaceous seas', Scientific American, April 2026.

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Move over, megalodon. An analysis of fossil jaws belonging to octopuses that lived between 100 million and 72 million years ago shows these creatures may have been the largest animals in the sea and smart to boot, rivaling sharks and marine reptiles in predatory power.

Large vertebrates have occupied the top of the marine food chain for the past 370 million years: sharks, ichthyosaurs, plesiosaurs and whales. In contrast, soft-bodied invertebrates seemed to serve only as prey. In the Late Cretaceous, giant marine reptiles called mosasaurs were thought to rule the seas unchallenged.

The new study suggests mosasaurs had competition from invertebrates. Shin Ikegami of Hokkaido University and colleagues examined fossils of giant octopuses dubbed krakens, after the sea monsters of Norwegian legend. Like modern octopuses, these Cretaceous krakens had a beak composed of two jaws made of a tough material called chitin. The team studied fossilized jaws and their wear patterns to reconstruct sizes and feeding behaviors.

The fossils came from Japan and Vancouver Island, Canada. They represent two species: N. jeletzkyi and N. haggarti. The larger species, N. haggarti, reached a total body length of up to 18.6 metres, comparable to an articulated bus. Todays giant squid reaches about 13 metres at most. N. haggarti may have been the biggest creature in Cretaceous seas.

These octopuses were also formidable predators. Because their stomach contents were not preserved, researchers studied damage to the beak caused by eating. The wear on the fossil jaws suggests both species were carnivores that crushed shells and hard bones. Although they lacked the long jaws of mosasaurs, they could use their long, flexible arms to seize large prey while dismantling it with powerful beaks.

The asymmetry of the wear hints that different parts of the brain were specialized for different tasks, a sign of advanced cognition in these invertebrates.

Large marine vertebrates and cephalopods independently evolved similar adaptations: both evolved jaws, improved feeding efficiency, and lost heavy protective coverings for faster swimming. These changes boosted body size and cognition, producing top predators in both groups.

Questions 1-5

Choose the correct letter, A, B, C or D.

1. When did the krakens live? A. 10,000 years ago B. 100 to 72 million years ago C. 370 million years ago D. Last century
2. What were the krakens beaks made of? A. Bone B. Chitin C. Shell D. Teeth
3. How long could N. haggarti grow? A. 13 metres B. 18.6 metres C. 37 metres D. 100 metres
4. How did researchers determine the krakens diet? A. By finding fossil stomach contents B. By studying wear patterns on the beak C. By comparing with modern octopuses D. By DNA analysis
5. The asymmetry of beak wear suggests what? A. The octopuses were left-handed B. Different brain parts were specialized for different tasks C. The beaks were broken D. The octopuses ate only plants

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. For 370 million years, large vertebrates have topped the marine food chain.
7. The fossils were found in Africa.
8. Modern giant squid can grow up to 18.6 metres.
9. The krakens had flexible arms.
10. Vertebrates and cephalopods evolved similar adaptations independently.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

The krakens were soft-bodied 11 that reached 18.6 metres. They crushed shells with their 12. Both vertebrates and cephalopods independently lost heavy coverings for faster 13.

Answers

1. B 2. B 3. B 4. B 5. B
2. TRUE 7. FALSE 8. FALSE 9. TRUE 10. TRUE
3. invertebrates 12. beaks 13. swimming

Key Vocabulary

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