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Giant bones change scientists’ thinking on why dinosaurs learned to walk on four legs

Jamie Seidel, October 21, 2018 6:42PM AP

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An illustration of the dinosaur named Ledumahadi Mafube. Picture: AFP media_cameraAn illustration of the dinosaur named Ledumahadi Mafube. Picture: AFP

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A newly described species of dinosaur described as “a giant thunderclap at dawn” could hold the answer to the age-old* question of why dinosaurs ended up walking on all fours*.

Tests on dinosaur bones found 30 years ago have led scientists to believe the move to four legs was because they became too heavy for their hind* legs to carry them.

An international team of scientists is studying Ledumahadi mafube, whose name means “a giant thunderclap at dawn” in the African Sesotho language. It weighed 12 tonnes and lived in southern Africa 200 million years ago. It was the largest land animal on Earth at the time and

an early example of the group that includes the great sauropod dinosaurs, the most famous of which is the Brontosaurus.

Four legs are visible on the dinosaur named Ledumahadi Mafube. Picture: AFP
media_cameraFour legs are visible on the dinosaur named Ledumahadi Mafube. Picture: AFP

Sauropods were the dominant plant-eating animal on Earth for 135 million years, and it is generally believed their success was due to their enormous size and ability to walk on all fours.

They were helped by specialised* column-like* legs, making them very good at carrying heavy weights — think of an elephant’s legs.

But when dinosaurs first evolved 240 million years ago, they were bipedal, meaning they walked on two legs.

Illustrations showing the differences in forelimb morphology between Ledumahadi and a normal sauropod. Beneath is a detail of the discovered fossilised remains and where they were placed. Source: supplied
media_cameraIllustrations showing the differences in forelimb morphology between Ledumahadi and a normal sauropod. Beneath is a detail of the discovered fossilised remains and where they were placed. Source: supplied

Palaeontologists* don’t know when and why some started walking on four legs — or, became quadrupedal — like the giant sauropods.

The researchers thought Ledumahadi could offer some clues because, while it was the size of a true sauropod, it came from an earlier lineage*, generally assumed to be two-legged.

Based on the thickness and weight-bearing capacity of its limbs, the palaeontologists determined this dinosaur was something of an oddity*: it was only “experimenting” with walking on all fours. It didn’t have the elephant-like posture of later dinosaurs.

The forelimbs on Ledumahadi were still highly flexible, however, making it crouch like a cat..

The position of Ledumahadi mafube in the evolutionary chain and, bottom, aa simplified geological map of the Elliot Formation in the Republic of South Africa and Lesotho, and the landscape of the Ledumahadi discovery site. Source: supplied
media_cameraThe position of Ledumahadi mafube in the evolutionary chain and, bottom, aa simplified geological map of the Elliot Formation in the Republic of South Africa and Lesotho, and the landscape of the Ledumahadi discovery site. Source: supplied

“This was the animal that wanted to have everything,” the study’s lead author, Blair McPhee of the University of São Paulo, told National Geographic.

“It wanted to be really big, like a sauropod, and wanted to walk predominantly quadrupedally, like a sauropod. But when it came to relinquishing* that primitive mobile forelimb, it didn’t want to do that.”

Professor Jonah Choiniere shows a fossilised rib head of the newly discovered species of dinosaur named Ledumahadi Mafub. Picture: AFP
media_cameraProfessor Jonah Choiniere shows a fossilised rib head of the newly discovered species of dinosaur named Ledumahadi Mafub. Picture: AFP

Jonah Choiniere, a palaeontologist at the University of Witwatersrand in Johannesburg and leader of the study published in Current Biology, said walking on all fours would have allowed dinosaurs like Ledumahadi to support a bigger gut size by distributing its weight over two sets of limbs.

And a bigger gut size, in turn, supports a bigger body.

“If you evolve the ability to walk on four legs, it actually facilitates* the evolution of large body mass,” Professor Choiniere said..

He said Ledumahadi would have been the giant of its time.

“If they were walking next to you, the ground would be thundering with their footsteps,” Professor Choiniere said.

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GLOSSARY

age-old: around for a long time

all fours: hands and feet

hind: back

specialised: expert in a particular subject or skill

column-like: like a thick pillar that supports weight

palaeontologists: scientists who study fossils

lineage: line of ancestors

oddity: something strange or peculiar

relinquishing: giving up

primitive: early stage of evolution

facilitates: allows

LISTEN TO TODAY’S STORY

QUICK QUIZ

1. What does Ledumahadi mafube mean?

2. How much did it weight?

3. What does bipedal mean?

4. Ledumahadi mafube had a posture similar to what other animal?

5. Which publication was the study published in?

CLASSROOM ACTIVITIES

1. Walking on all fours

Design and create a diagram or set of diagrams that will help another student understand how and why dinosaurs ended up walking on all fours. Don’t forget to use labels to make your diagram as clear and interesting as possible.

Time: Allow 25 minutes

Curriculum Links: Science, English.

2. Extension

Write an acrostic about dinosaurs using the words “ a giant thunderclap at dawn”. An acrostic is a poem where the first word in each line starts with the letter in the words.

Time: Allow 25 minutes.

Curriculum Links: English, Science.

VCOP ACTIVITY

The glossary of terms helps you to understand and learn the ambitious vocabulary being used in the article. Can you use the words outlined in the glossary to create new sentences? Challenge yourself to include other VCOP (vocabulary, connectives, openers and punctuation) elements in your sentence/s. Have another look through the article, can you find any other Wow Words not outlined in the glossary?

HAVE YOUR SAY: What is your favourite dinosaur and why?

No one-word answers. Use full sentences to explain your thinking.

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