Bone Study Suggests Dinosaur Size not Linked to Growth Rate

A new study has found that a dinosaur's size was not necessarily linked to how quickly it grew.

The research results come from studying a group of dinosaurs¹ called theropods. Some theropods, like the meat-eating Tyrannosaurus rex, could grow to about the size of a bus. Others were much smaller, including some that grew to about the size of a cat.

Scientists have long believed that theropods generally followed a set pattern for growth. It was thought that dinosaurs that grew the fastest also got bigger than other theropods. And the ones that grew slower were believed to grow up to be smaller.

But the new study – which recently appeared in the publication Science – raises questions about that theory.

The researchers examined rings called "cortical growth marks" in different theropod species². The marks appeared inside the dinosaurs' bones each year. They are similar to rings inside a tree that can be counted to tell how old the tree is. Widely spaced rings suggest a faster growth rate, while closely spaced rings suggest slower growth.

The scientists found no common pattern linked to body size. Some huge theropods grew quickly and stopped growing, while some grew slower over a longer period of time to reach the same size. Some small theropods grew quickly and others grew slowly.

Mike D'Emic is a professor of biology at Adelphi University in New York City. He was the lead writer of the study. D'Emic told Reuters news agency the latest research "overturns³" past thinking about the growth of theropods.

He added that the study suggests other groups should also be studied to see if the research results hold up with other animals.

"It's equally likely that an animal evolved larger body size by growing at the same rate for longer, rather than just growing faster," D'Emic said. "It is surprising and important to know that animals are just as likely to evolve to gigantic⁴ sizes at slow rates."

The study found that Tyrannosaurus rex – which could grow to 12 meters long – was an example of a big and fast-growing theropod. Acrocanthosaurus – which is a bit smaller than T. rex – was an example of a big but slow-growing theropod.

The researchers said the 2-meter-long Coelophysis was a fast-growing, smaller theropod. Xixianykus, one of the tiniest dinosaurs at 50 centimeters long, was a small and slow-growing theropod.

The study found that Spinosaurus – a 15-meter theropod that spent time on land and in the water – grew much more slowly than Tyrannosaurus. And it found that Mapusaurus, which reached about 11.5 meters, grew even faster than Tyrannosaurus.

Patrick O'Connor is an evolutionary⁵ biologist and was a co-writer of the study. He told Reuters that the study should open the door to new research about how growth rates are connected to the size of many different animal groups.

Words in This Story

pattern – n. a regular and repeated way in which something happens

species – n. a group of animals or plants that are similar and can produce young animals or plants

evolve – v. to develop or make something develop over time

gigantic – adj. very large

tiny – adj. very small

evolution – n. the way in which living things gradually change and develop over millions of years

1 dinosaurs   

n.恐龙( dinosaur的名词复数 )；守旧落伍的人，过时落后的东西

参考例句：

• The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
• Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》

2 species   

n.物种，种群

参考例句：

• Are we the only thinking species in the whole of creation?我们是万物中惟一有思想的物种吗？
• This species of bird now exists only in Africa.这种鸟现在只存在于非洲。

3 overturns   

（使）翻倒( overturn的第三人称单数 )； 使垮台，推翻； 撤销（判决等）

参考例句：

• It overturns economic policies. 它无视经济政策。
• It overturns child-raising theory. 它推翻了儿童抚养理论。

4 gigantic   

adj.巨大的，巨人似的

参考例句：

• He has a gigantic appetite and eats gigantic meals.他有很大的食量，能吃很多的食物。
• The earth may be thought of as a gigantic magnet.整个地球可以想像为一块硕大无朋的磁石。

5 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• Life has its own evolutionary process.生命有其自身的进化过程。
• These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。