Ever wondered how many Tyrannosaurus rex (霸王龙) ever walked around the Earth? The answer is 2.5 billion over the two million or so years in which the species existed, according to a calculation published today in Science. The figure has allowed researchers to estimate just how rare it is for animals to fossilize.
Researchers led by Charles Marshall used a method employed by ecologists studying contemporary creatures to estimate the population of T. rex during the late Cretaceous period.
The team used their estimates of the total range of T. rex across modern North America, combined with their estimates of the dinosaur’s weight, to calculate that, at one time, around 20,000 T. rex would have been alive on the planet. That translates to around 3,800 T. rex in an area the size of California, or just 2 T. rex moving around Washington DC. Calculating that T. rex survived for about 127,000 generations before disappearing, the researchers came up with a figure of 2.5 billion individuals over the species’ entire existence. Only 32 adult T. rex have been discovered as fossils, so the fossil record accounts for just 1 in about every 80 million T. rex. This means that the chances of being fossilized were small.
These numbers suggest that fossils in general are rare, and that many species that were less widespread than T. rex were probably never preserved, says Marshall, who adds, “The fossil record is our only direct knowledge of these past histories of our planet.”
Thomas Holtz, a researcher, says that “we always knew that the chance of any individual becoming a fossil was rare, but we lacked the calculation to figure out how rare”.
But he says it would be good “to see someone ground-truth these kinds of estimates against living species to get a better sense of accuracy”. He’d also like to see comparable studies made on disappearing species with more abundant fossils, which might allow us to better understand historic ecosystems.
12. Which of the following was used to figure out the population of T. rex?
A.The method used by researchers to study fossils. |
B.The approach to calculate kinds of wildlife. |
C.The way applied by ecologists to study modern creatures. |
D.The system to compare various studies on disappearing species. |
13. How does the author develop the third paragraph?
A.By making a comparison. | B.By listing the figures. |
C.By giving an explanation. | D.By presenting examples. |
14. What can we infer from paragraph 4?
A.T. rex owns quite a few fossils. |
B.The fossils record all the past of our planet. |
C.Many species lived together in their whole life. |
D.Fossils of some species may never be stored. |
15. Which of the following could be the best title for the text?
A.The Figure of T. rex Helps Calculate How Rare Their Fossils Are |
B.Scientists Applied Fossils to Understand Past Ecosystems |
C.A New Method to Figure out the Number of T. rex |
D.The Fossil Record to Uncover the History of Our Planet |