An ancient tusked creature that lived on Antarctica 250 million years ago was the first known animal to survive by hibernating, according to a new study.
Called Lystrosaurus, it looked like a cross between a giant pig and a lizard and slept for days, weeks or even months on end to get through the long, dark nights.
This is the earliest known example of hibernation ever found by palaeontologists in an animal and goes back to Pangea, according to a team from Harvard University.
Hibernation is a familiar feature today. Many animals living near or within polar regions do it to get through dark winter months when food is scarce.
The new discovery, involving taking a thin slice from Lystrosaurus tusk and looking at ‘stress rings’, proves that hibernation has been around since before the dinosaurs.
Called Lystrosaurus, it looked like a cross between a giant pig and a lizard and slept for days, weeks or even months on end to get through the long, dark nights
Megan Whitney, then a University of Washington doctoral student, excavating fossils in Antarctica in 2017. Whitney is now a palaeontologist at Harvard University
Paleontologists searching for fossils in Antarctica in 2017. Lystrosaurus was an early relative of mammals and it thrived in what is now Russia, China, India, Africa and Antarctica – which at the time may have been forested
Lead author Dr Megan Whitney said the stress marks in the tusks are similar to marks in teeth associated with hibernation in certain modern animals.
Lystrosaurus was an early relative of mammals and it thrived in what is now Russia, China, India, Africa and Antarctica – which at the time may have been forested.
HIBERNATION: A SLOWING OF THE METABOLISM
Certain animals are able to enter a state of minimal activity and metabolic depression for periods of time.
This is known as hibernation and it is characterised by low body-temperature, slow breathing and heart-rate, and low metabolic rate.
It most commonly occurs during winter months, allowing creatures to stave off food shortages and freezing temperatures.
A wide range of creatures from butterflies to bears use it to survive the cold without having to forage for food or migrate somewhere warmer.
New research has dated the earliest example of a hibernating creature back 250 million years to the pig/lizard-like Lystrosaurus.
The stout and squat four legged forager could reach eight feet long and had no internal teeth – just a pair of tusks protruding from its upper jaw.
These enabled it to dig for roots, tubers and other vegetation, according to the researchers writing in the Communications Biology journal.
Like those of elephants, the tusks grew continuously throughout their lives.
Fossilised remains can harbour information about metabolism, growth and stress or strain on the body, according to the Harvard team.
They compared cross-sections of tusks form six specimens in Antarctica and four from South Africa and they all showed similar growth patterns.
But they were thick and close together in the Antarctic fossils – a feature absent from the others taken from South Africa.
This indicated there was less of the hard, dense, bony tissue found in tusks and teeth – likely due to prolonged stress from longer days and colder nights.
Lystrosaurus may have undergone complete hibernation – a weeks-long reduction in metabolism, body temperature and activity, the team said.
‘Lystrosaurus in Antarctica likely needed some form of hibernation-like adaptation to cope with life near the South Pole,’ Whitney said.
Earth was much warmer during the Triassic than today – and parts of Antarctica may have been forested but there was still annual variations in the amount of daylight.
Dr Whitney said many other ancient vertebrates at high latitudes may also have used torpor – including full hibernation – to cope with the strains of winter.
But famous extinct animals – including the dinosaurs that evolved and spread after Lystrosaurus died out – don’t have teeth that grow continuously.
Co-author Professor Christian Sidor, of the University of Washington, Seattle, said this was an important requirement to find signs of hibernation in dead creatures.
LYSTROSAURUS: HERBIVOROUS CREATURES SIMILAR TO LIZARDS AND PIGS
Lystrosaurus is a type of dicynodont, a major group of primarily herbivorous vertebrates during the Triassic era.
They are characterised by their turtle-like beaks and ever-growing tusks.
They are distantly related to modern mammals – dating back 250 million years and range in size from a corgi to slightly smaller than a cow.
Fossils of Lystrosaurus are known from China, Russia, India, South Africa and Antarctica – once parts of Pangea.
Latest research from rings in their tusks show that they were the earliest known hibernating species.
‘To see the specific signs of stress and strain brought on by hibernation, you need to look at something that can fossilise and was growing continuously during the animal’s life. Many animals don’t have that, but luckily Lystrosaurus did,’ Sidor said.
Analysis of additional Lystrosaurus fossils may also settle another debate about these mysterious, prehistoric creatures, said Whitney.
‘Cold-blooded animals often shut down their metabolism entirely during a tough season but many warm blooded animals that hibernate frequently reactivate their metabolism during this period.
‘What we observed in the Antarctic Lystrosaurus tusks fits a pattern of small metabolic ‘reactivation events’ during a period of stress, which is most similar to what we see in warm-blooded hibernators today,’ the researcher said.
She added: ‘Animals that live at or near the poles have always had to cope with the more extreme environments present there.
‘These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one.’
If so, this distant cousin of mammals isn’t just an example of a hearty creature. It is also a reminder that many features of life today may have been around for hundreds of millions of years before humans evolved to observe them.
Lystrosaurus lived during a dynamic period of our planet’s history, arising just before the ‘Great Dying’ at the end of the Permian Period 252 million years ago.
It was triggered by a massive volcanic eruption that ran for almost one million years in what is today Siberia. Around 90 per cent of marine species were also wiped out.
This thin-section of the fossilised tusk from an Antarctic Lystrosaurus shows layers of dentine deposited in rings of growth. The tusk grew inward, with the oldest layers at the edge and the youngest layers near the center, where the pulp cavity would have been
University of Washington paleontologist Christian Sidor excavating fossils in Antarctica in 2017
Co-author Professor Christian Sidor (pictured), of the University of Washington, Seattle, said examining the rings from tusks that continuously grow is the best way to see signs of hibernation
At the time Earth’s land mass comprised one ‘supercontinent’ Pangaea – which included what is now Antarctica.
Back in the Triassic, the collection sites in Antarctica were at about 72 degrees south latitude – well within the Antarctic Circle, at 66.3 degrees south.
The collection sites in South Africa were more than 550 miles north during the Triassic at 58-61 degrees south latitude, far outside the Antarctic Circle.
Sidor added: ‘The fact Lystrosaurus survived the end-Permian mass extinction and had such a wide range in the early Triassic has made them a very well-studied group of animals for understanding survival and adaptation.’
The findings have been published in the journal Communications Biology.
A map of Pangea during the Early Triassic, showing the locations of the Antarctic (blue) and South African (orange) Lystrosaurus populations compared in this study
THE BIG FIVE MASS EXTINCTIONS
The first of the big five extinction events took place around 540 million years ago was the second biggest extinction event of marine life. There was only life in the seas at this time and more than one hundred families of marine invertebrates died.
Late Devonian extinction
About 375 million years ago, major environmental changes caused a drawn-out extinction event that wiped out 70% of marine species
Permian-Triassic extinction (the Great Dying)
The largest extinction event and the one that affected the Earth’s ecology most profoundly took place 251 million years ago. As much as 90-95% went extinct, and it took about 50 million years for life on land to fully recover its biodiversity – with the rise of many species of dinosaurs.
Dinosaurs first appeared in the Early Triassic, but large amphibians and mammal-like reptiles were the dominant land animals. The rapid mass extinction that occurred 205 million wiped out about 20% of all marine families, many reptiles and the last of the large amphibians – opening up niches for the dinosaurs of the Jurassic.
The Cretaceous-Tertiary (KT) extinction
Many researchers believe that an asteroid slammed down on Earth 65-66 million years ago at Chicxulub, Mexico. The impact is often blamed for ending the reign of the dinosaurs. It took 10 million years for biodiversity to recover from this mass extinction.
Many researchers believe that an asteroid slammed down on Earth 65-66 million years ago at Chicxulub, Mexico. The impact is often blamed for ending the reign of the dinosaurs. It took 10 million years for biodiversity to recover from this mass extinction
Source: University of California, Riverside