How is it that crocodiles have survived long after the dinosaurs perished?<\/p>\n
Researchers believe they may know how the apex predators* survived a mass extinction event 66 million years ago that wiped out three quarters of Earth\u2019s species, including the dinosaurs.<\/p>\n
And it has to do with keeping warm.<\/p>\n
RESEARCH TRACKS PREHISTORIC CROC MOVEMENT
Crocodilians \u2014 today\u2019s crocodiles, alligators, caimans and gharials and their many extinct<\/p>\n
relatives \u2014 have been a roaring success since coming into existence more than 240 million years ago. And new research identifies one important factor in their success \u2014 sticking to warm climates throughout their history.<\/p>\n
In fact, the researchers said, this trait may help explain why crocs as a group survived the asteroid strike 66 million years ago that doomed the dinosaurs, along with certain physiological* characteristics that make them one tough bunch of reptiles.<\/p>\n
The crocodilian evolutionary lineage*, called Pseudosuchia, arose during the Triassic* Period in the aftermath of Earth\u2019s worst mass extinction event at the end of the Permian*, known as \u201cthe Great Dying\u201d (about 250 million years ago).<\/p>\n
In fact, early crocs appeared on the scene millions of years before the first dinosaurs and mammals.<\/p>\n
The researchers tracked the geographic range for crocs during their entire history, guided by an evolutionary tree of more than 400 extinct and living species. They used data from more than 7,000 fossils and geographic records of modern crocs such as the alligators of Florida, saltwater crocodiles of Australia, gharials of India, caimans of Brazil and more.<\/p>\n
They combined this information with 52 global palaeoclimate* reconstructions to determine the climatic conditions under which crocs lived over time. While other groups such as dinosaurs and mammals conquered a variety of climates, the study showed that crocs consistently kept to warm climates.<\/p>\n
\u201cRather than continually adapting to new climatic conditions, they largely tracked suitable environments as these shifted geographically, expanding towards the poles during<\/p>\n
warmer periods and retreating towards the equator during cooler ones,\u201d said University College London vertebrate palaeontologist* Alfio Alessandro Chiarenza, lead author of the research published in the journal Science Advances.<\/p>\n
For example, during an exceptionally warm moment in Earth\u2019s history around 50 million years ago, Dr Chiarenza said, crocs inhabited high-latitude* regions of North America, Europe and even Antarctica.<\/p>\n
\u201cOne of the most striking patterns is the repeated expansion* and contraction* of suitable habitat in response to global temperature changes,\u201d Dr Chiarenza said.<\/p>\n
DIFFERENT TYPES OF PREHISTORIC CROCS
While living crocs are primarily semiaquatic* ambush predators*, their extinct relatives included a broad variety of forms, University College London palaeontologist and study co-author Philip Mannion said.<\/p>\n
\u201cThey have occupied almost every conceivable* ecological* role,\u201d Dr Chiarenza said.<\/p>\n
There were fully land-dwelling apex predators like 9m long Fasolasuchus, pug-snouted herbivores like Simosuchus, armoured plant-eaters like Aetosaurus, mollusc-eaters like Kuttanacaiman, filter-feeders like Mourasuchus and ocean-going types like Metriorhynchus.<\/p>\n
And if you thought modern-day crocodiles were scary enough, during the age of dinosaurs, there also were semiaquatic crocs like Deinosuchus, which measured up to 12m long and may have rivalled the Tyrannosaurus in mass.<\/p>\n
\u201cModern crocodilians are only the surviving remnants of a once extraordinarily diverse evolutionary group,\u201d Dr Chiarenza said.<\/p>\n
DINOSAUR APOCALYPSE
The asteroid strike at a site called Chicxulub off the coast of Mexico\u2019s Yucat\u00e1n Peninsula at the end of the Cretaceous* period unleashed a global environmental cataclysm*. Three-quarters of Earth\u2019s species including the dinosaurs, aside from their bird descendants, vanished.<\/p>\n
The crocs survived.<\/p>\n
\u201cThe Chicxulub impact caused a dramatic reduction in incoming sunlight, producing an impact winter* and widespread environmental disruption. However, our climate simulations<\/p>\n
suggest that this cooling did not affect the availability of suitable climatic conditions* equally for all groups,\u201d Dr Chiarenza said.<\/p>\n
\u201cUnder all but the most extreme impact scenario we tested, tropical and subtropical regions retained climatic conditions suitable\u201d for the crocs, Dr Chiarenza said, explaining that there were likely still warm areas inhabited by crocs after the asteroid strike.<\/p>\n
The findings suggest that the longstanding preference of crocs for warm and low-latitude* environments may have placed some surviving populations in areas that were sheltered from the freezing, dark conditions caused by the impact. These regions would have been near the equator and in the subtropics where climatic conditions stayed warm and within the range the crocs were accustomed to, Dr Chiarenza said.<\/p>\n
For dinosaurs, however, the impact caused a collapse of suitable habitat.<\/p>\n
OTHER REASONS CROCS SURVIVED
Crocs also possess physiological traits beneficial for times of environmental stress. They can enter states of dormancy* to cope with harsh conditions, such as aestivation* to survive extreme heat or drought, and brumation* to withstand extreme cold. Crocs today, for instance, may dig burrows or encase themselves in hardened mud during severe droughts, slowing their heartbeat and breathing.<\/p>\n
Dr Chiarenza said the ability to conserve energy using these states of dormancy could have been very beneficial following the Chicxulub impact, when sunlight was scarce and there were less species to feed on.<\/p>\n
Crocs are also cold-blooded, while recent research suggests that at least some dinosaurs, such as the Tyrannosaurus, were warm-blooded. Bodily requirements for cold-blooded animals are much lower than for comparably sized warm-blooded animals.<\/p>\n
\u201cThat can become a significant advantage when food becomes scarce. Crocodilians can survive extended periods without feeding,\u201d Dr Chiarenza said. \u201cBut even if an animal can survive prolonged starvation, it still needs environmental conditions that remain within its physiological limits.\u201d<\/p>\n
Minor edits have been made to this story for Kids News. Reuters reporting by Will Dunham in Washington; Editing by Daniel Wallis<\/p>\n
POLL <\/p>\n
GLOSSARY<\/p>\n
apex predators: an animal at the top of a food chain that has no predators hunting it physiological: relating to the way the bodies of living things function lineage: direct line of descent from a common ancestor Triassic: the Triassic period was from about 252 million years ago to 201 million years ago, following the mass extinction event at the end of the Permian called \u201cthe Great Dying\u201d which was the largest mass extinction Earth has ever known, and leading to the Jurassic period Permian: the Permian period was from about 298.9 million years ago to about 251.9 million years ago and was the final period of the Paleozoic Era. During this period, all of Earth\u2019s major landmasses came together to form the supercontinent Pangaea palaeoclimate: the climate during a past geological age, before the invention of weather instruments and meteorological records palaeontologist: a scientist who studies the history of life on Earth through the examination of fossils high-latitude: regions that are situated far from the equator, stretching from subpolar areas towards the North and South Poles expansion: widening contraction: shrinking semiaquatic: living on both land and in water ambush predators: a meat-eating animal that catches prey by using camouflage, patience or luring rather than chasing them over long distances conceivable: possible to imagine, think of or believe ecological: the relationships between living creatures and their physical environment Cretaceous: the final period of the Mesozoic Era (lasting from about 145 to 66 million years ago), in which dinosaurs like the Tyrannosaurus rex and Triceratops roamed the Earth and the supercontinent Pangaea continued to break apart, sending continents toward the positions they are in today while raising global sea levels cataclysm: a sudden, violent event that causes great destruction impact winter: a potential period of prolonged global cooling that scientists think was caused by the impact of an asteroid or comet striking the Earth climatic conditions: the long term weather patterns and atmospheric conditions in a geographical region over a period of time, typically 30 years or more low-latitude: the geographic region on Earth that lies closest to the equator, between 0 and 30 degrees north or south latitude. These regions are typically describes as the tropics or subtropics and feature warm to hot weather year-round because the sun hits this part of the Earth consistently dormancy: a state of temporary inactivity, reduced metabolic function or slowed growth that helps an animal conserve energy and survive harsh conditions aestivation: a state of dormancy in animals to survive extreme heat brumation: a state of sluggishness or winter dormancy in animals exhibited by cold-blooded animals during cold weather <\/p>\n
EXTRA READING QUICK QUIZ LISTEN TO THIS STORY<\/p>\n CLASSROOM ACTIVITIES Time: allow 45 minutes to complete this activity 2. Extension Time: allow 15 minutes to complete this activity VCOP ACTIVITY Then back up the main idea with two to four key points to support what you first stated.<\/p>\n What would you put as the main idea and supporting points to back up this article?<\/p>\n Once you have had a go at note-taking.<\/p>\n Share your results with a peer to see if you identified the same information or different.<\/p>\n Discuss the finding if you came up with different information.<\/p>\n","protected":false},"excerpt":{"rendered":"How is it that crocodiles have survived long after the dinosaurs perished? 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\u2018Drop crocs\u2019 roamed Australia<\/a>
Young dinosaur was crocodile\u2019s last meal<\/a>
T-rex eye evolved for bigger bite<\/a><\/p>\n
1. How long ago did the crocodilian family come into existence?
2. What was the mass extinction event that wiped out the dinosaurs but not the crocodiles?
3. When did this event occur?
4. What is one reason crocodiles are thought to have survived the extinction event?
5. What effect did the mass extinction event have on Earth\u2019s climate?<\/p>\n
1. What\u2019s the difference?
Australians will probably be familiar with crocodiles, as we have them here in our country. But we might be less familiar with alligators, gharials and caimans. Research to find out about the four types of crocodilians, then make a one-page \u2018cheat sheet\u2019 that will help readers understand the similarities and differences between these creatures. You might include key information such as where they live, their size, what they eat, etc. as well as pictures or diagrams.<\/p>\n
Curriculum Links: English; Science<\/p>\n
Based on what you now know about why crocodilians have survived for 240 million years while other species have been wiped out, name another animal that you think could survive another asteroid strike like the one 66 million years ago. Explain your reasons for believing this animal could survive.<\/p>\n
Curriculum Links: English; Science<\/p>\n
Let\u2019s practise taking notes
When note-taking, we want to be able to extract the key pieces of information from the text or presentation. You start with determining the main idea: if you had to explain to someone in a sentence what the article is about, what would you say?<\/p>\n