Mammals developed arms before dinosaurs even existed! Forelimbs such as flippers on dolphins and wings on bats emerged 270 million years ago
- Mammal forelimbs began to diversify 30 million years before the first dinosaurs
- Researchers studied the earliest fossil relics of our mammal ancestors
- The synapsids were land dwelling and the sauropids went on to be dinosaurs
- Synapsids eventually branched into the therapsids, the group we’re in today
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Human arms and other mammal forelimbs began to diversify 270 million years ago, 30 million years before the first dinosaurs.
No other group of vertibrates, or all animals with spinal cords, has evolved so many different kinds of arms as mammals tailored for the varying habitats and lifestyles.
Examples of the different types of mammal forelimbs include flippers on dolphins, wings on birds, and practically all lizards walk on all fours.
Scientists have discovered that our early relatives started evolving diverse forelimbs before the earliest dinosaurs existed.
Prior to this, the earliest that paleontologists had been able to definitively trace back mammals’ diverse forelimbs was 160 million years ago.
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Photographs of the upper arm bones from seven kinds of early mammal relatives. The three bones on the left are from an early group called pelycosaurs and the four bones on the right are from therapsids, the group that includes today’s mammals. The black bars represent 2cm
The study helps explain how mammals evolved traits and a variety of different forelimb shapes that have make each mammal what they are today.
The team, from the University of Chicago, studied the earliest fossil relics of our mammal ancestors the synapsids and the sauropids.
Synapsids, which were land dwelling vertebrates, split away from the sauropsids, which went on to include dinosaurs, birds, crocodiles, and lizards.
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Splitting about 312 million years ago, the synapsids eventually branched into therapsids who began evolving diverse forelimbs 270 million years ago.
Study author Jacqueline Lungmus, a research assistant at Chicago’s Field Museum and a doctoral candidate at the University of Chicago said: ‘Aside from fur, diverse forelimb shape is one of the most iconic characteristics of mammals.
‘We were trying to understand where that comes from, if it’s a recent trait or if this has been something special about the group of animals that we belong to from the beginning.’
A key difference between sauropsids and synapsids is the pattern of openings in the skull where jaw muscles attach.
While the earliest synapsids, called pelycosaurs, were more closely related to humans than to dinosaurs, they looked like hulking reptiles.
Ophiacodon, an early mammal relative from before the group began developing diverse forelimbs. Scientists have discovered that our early relatives started evolving diverse forelimbs before the earliest dinosaurs existed
Study co-author and Field Museum curator Ken Angielczyk, said: ‘If you saw a pelycosaur walking down the street, you wouldn’t think it looked like a mammal – you’d say, ‘That’s a weird-looking crocodile.’
Ms Lungmus explained how it was the sometime furry therapsids who began to branch out.
She said: ‘Modern mammals are the only surviving therapsids. This is the group that we’re part of today.
‘Therapsids were the first members of our family to really branch out. Instead of just croc-like pelycosaurs, the therapsids included lithe carnivores, burly-armed burrowers, and tree-dwelling plant-eaters.’
The research says it might have been the forelimb that drove this diversification.
Ms Lungmus continued: ‘This is the first study to quantify forelimb shape across a big sample of these animals.’
The team examined the upper arm bones of hundreds of fossil specimens representing 73 kinds of pelycosaurs and therapsids, taking measurements near where the bones joined the shoulder and the elbow.
When they compared the shapes of arm bones, the researchers found a lot more variation in the bones of the therapsids than the pelycosaurs.
This is Thrinaxodon, a therapsid animal related to today’s mammals. The therapsids are the group where mammal relatives began developing diverse forelimbs. The study says it might have been the forelimb that drove the diversification
They also noted that the upper part of the arm, near the shoulder, was especially varied in therapsids allowing them to move more freely than the bulky pelycosaurs.
They found that a wide variety of different forelimb shapes evolved within the therapsids 270 million years ago.
Ms Lungmus said: ‘The therapsids are the first synapsids to increase the variability of their forelimbs. This study dramatically pushes that trait back in time.
‘Prior to this study, the earliest that paleontologists had been able to definitively trace back mammals’ diverse forelimbs was 160 million years ago.
‘Our work has pushed this back by more than a hundred million years.’
‘This is something that’s so cool about our evolutionary lineage.
‘These animals are in the same group as us. Part of what makes this research compelling is that these are our relatives.’
The findings are published in the Proceedings of the National Academy of Sciences.
WHY DID THE DINOSAURS GO EXTINCT?
Dinosaurs ruled and dominated Earth around 66 million years ago, before they suddenly went extinct.
The Cretaceous-Tertiary extinction event is the name given to this mass extinction.
It was believed for many years that the changing climate destroyed the food chain of the huge reptiles.
In the 1980s, paleontologists discovered a layer of iridium.
This is an element that is rare on Earth but is found in vast quantities in space.
When this was dated, it coincided precisely with when the dinosaurs disappeared from the fossil record.
A decade later, scientists uncovered the massive Chicxulub Crater at the tip of Mexico’s Yucatán Peninsula, which dates to the period in question.
Scientific consensus now says that these two factors are linked and they were both probably caused by an enormous asteroid crashing to Earth.
With the projected size and impact velocity, the collision would have caused an enormous shock-wave and likely triggered seismic activity.
The fallout would have created plumes of ash that likely covered all of the planet and made it impossible for dinosaurs to survive.
Other animals and plant species had a shorter time-span between generations which allowed them to survive.
There are several other theories as to what caused the demise of the famous animals.
One early theory was that small mammals ate dinosaur eggs and another proposes that toxic angiosperms (flowering plants) killed them off.
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