The Evolutionary Mystery: Crocodile Survives
Read The Evolutionary Mystery: Crocodile Survives and check the IELTS Reading answers. Even though crocodiles have existed for 200 million years, they're anything but primitive. As crocodiles' ancestors, crocodilia came to adapt to an aquatic lifestyle. When most of the other contemporary reptiles…
Passage preview
Even though crocodiles have existed for 200 million years, they're anything but primitive. As crocodiles' ancestors, crocodilia came to adapt to an aquatic lifestyle. When most of the other contemporary reptiles went extinct, crocodiles were able to make it because their bodies changed and they adapted better to the climate. They witnessed the rise and fall of the dinosaurs, which once ruled the planet, and even the 65 million years of alleged mammalian dominance didn't wipe them off. Nowadays, the crocodiles and alligators are not that different from their prehistoric ancestors, which proves that they were (and still are) incredibly adaptive.
Vocabulary from this passage
9 words worth learning before you sit the test, each with the sentence it appears in.
- aestivation noun
Prolonged dormancy of an animal during a hot or dry period to avoid heat and desiccation
Aestivation is a critical survival strategy for crocodiles living in regions with a distinct dry season.
- contemporary adjective
Living or occurring at the same time; belonging to the same period as something else
While many contemporary reptiles went extinct, the crocodilian lineage managed to survive various climate shifts.
- electrolyte concentration noun
The amount of essential minerals, such as sodium or potassium, present in a fluid or tissue
The study tracked electrolyte concentrations to ensure the animals were not suffering from severe dehydration.
- metabolism noun
The chemical processes within a living organism that are necessary to maintain life and provide energy
A slow metabolism enables large reptiles to survive for months in environments with scarce food.
- nitrogenous waste noun
Waste products containing nitrogen, such as urea or ammonia, produced during the metabolism of proteins
Researchers monitored the accumulation of nitrogenous waste in the blood during the animal's dormant period.
- poikilothermal adjective
An organism whose internal body temperature varies considerably with the temperature of its surrounding environment
Being poikilothermal, the crocodile must bask in the sun to regulate its internal body heat.
- proportional adjective
Corresponding in size or amount to something else; maintaining a constant ratio between two variables
The loss of water during dormancy was proportional to the decrease in overall body weight.
- quiescent state noun
A period of inactivity or dormancy during which biological processes are significantly slowed or suspended
During periods of extreme drought, the animal enters a quiescent state to conserve vital energy.
- volatile environment noun
A habitat characterized by rapid, unpredictable changes, especially in climate or resource availability
The species evolved unique physiological traits to survive in the volatile environments of the tropical wetlands.
Answers with explanations
- 14. ix
Paragraph A discusses how crocodiles have existed for 200 million years, outliving dinosaurs and mammals due to adaptation. This focuses on their historical timeline and ability to endure, perfectly matching heading **ix** (A historical story for the supreme survivors).
- 15. iv
Paragraph B details the physical features of crocodiles (streamlined body, long tail, webbed legs) and explicitly states not to underestimate their capacity to **move on the ground**. This points directly to heading **iv** (The perfectly designed body for a great land roamer).
- 16. iii
Paragraph C focuses entirely on the crocodile's body temperature regulation and specifically highlights their **slower metabolism**, allowing them to survive extreme food shortages. This clearly aligns with heading **iii** (Slow metabolism which makes crocodile a unique reptile).
- 17. v
Paragraph D discusses the crocodile's efficient hunting techniques and explicitly states they are capable of **switching feeding methods** (chasing fish, snatching birds, ambushing). This matches heading **v** (Shifting eating habits and food intake).
- 18. i
Paragraph E explains how crocodiles survive the drought by digging holes and entering a state called aestivation. It shows how they turn the negative **impact of a drought** into a survival mechanism, corresponding to heading **i** (The favourable feature in the impact of a drought).
- 19. vi
Paragraph F introduces a specific **six-year study** by Kennett and Christian tracking the aestivation mechanism. The focus is entirely on the methodology of this research project, matching heading **vi** (A project on a special mechanism).
- 20. ii
Paragraph G details the results of the aforementioned study, noting the unexpected discovery that aestivating animals had no dehydration or harmful effects despite long starvation. This unique biological discovery aligns perfectly with heading **ii** (A unique finding that was recently achieved).
- 21. ["hot season","dry season"]
The summary needs a noun phrase detailing what brings the drought. The passage mentions that the **hot season** (or dry season in para F) brings drought to their habitats. 'Hot season' perfectly fits the requirement.
- 22. four months
The sentence requires a timeframe indicating how long aestivating crocodiles spend underground. The text explicitly states they spent **four months** a year underground, making it the correct answer.
- 23. water resources
The blank requires a noun phrase describing what the crocodiles had no access to while underground. The text states they were underground without access to **water resources**. It fits both grammatically and factually.
- 24. body weight
The sentence explains that water decline is proportional to something else. The text confirms that the loss of water reserves is proportional to the loss of **body weight**. 'Body weight' perfectly fills the conceptual and grammatical blank.
- 25. dehydration
The blank asks what negative sign is missing after aestivation. The text explicitly states that upon emerging, the animals had no **dehydration** and displayed no other harmful effects. The noun fits the sentence perfectly.
- 26. growth
The summary notes the crocodiles endured drought without slowing their speed of something. The text mentions they displayed no harmful effects such as a slowed-down **growth** rate. The noun 'growth' fits the blank perfectly.