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Explosion in snake diversity after dinosaur extinction
Snakes saw an explosion in diversity after the dinosaurs were wiped out by an asteroid, researchers have found.
Following the mass extinction of many dinosaurs, as well as flying and aquatic reptiles, snakes rapidly diversified from as few as six lineages to include many ancestors of the species we see today. This is probably due to the reptiles taking up many of the ecological roles that small dinosaurs had before their extinction.
Research led by the University of Bath also found a similar event taking place around 34 million years ago, when another large extinction event is known to have taken place.
Their findings, published in Nature Communications, further reinforce the role of mass extinctions in shaping the natural world as we know it today as the planet goes through a potential sixth event.
Dr Nick Longrich, from the Milner Centre for Evolution at the University of Bath, says, 'Our research suggests that extinction acted as a form of "creative destruction"- by wiping out old species, it allowed survivors to exploit the gaps in the ecosystem, experimenting with new lifestyles and habitats.
'This seems to be a general feature of evolution - it's the periods immediately after major extinctions where we see evolution at its most wildly experimental and innovative.
'The destruction of biodiversity makes room for new things to emerge and colonize new landmasses. Ultimately life becomes even more diverse than before.'
The line between the dark and light rocks marks the KT event. Image by Glenlarson, licensed via Wikimedia Commons.
Here today, gone tomorrow
Extinctions are nothing new and are a fundamental part of life on Earth. As conditions change, species adapt as best they can to their changing circumstances. If they can't adapt quickly enough, they die out and other species will eventually move in to take up their role in the environment.
Animals and plants are coming into existence and going extinct all the time. But at certain points in Earth's history, the rate of extinction has shot up. The largest of these are mass extinction events, where at least 75% of the planet's species are lost within a few million years.
To date there have been five of these, with support among some scientists that the current impact of human activity on the world is creating a sixth. The last commonly agreed mass extinction event was the Cretaceous mass extinction event, when a large meteor around 10 kilometres in diameter struck Earth off the coast of Mexico.
This caused shockwaves, tsunamis and a wave of heat that instantly killed many animals. Dust entering the atmosphere would have blocked out the Sun and caused photosynthesis to plummet, leaving many of the survivors to starve.
With many dinosaurs wiped out, the ancestors of modern mammals, birds and fish had a chance to flourish. Reptiles were in a similar position, with the generally smaller survivors able to take advantage of shelter and scarce food in the wake of the disaster.
Researchers found that at least six snake lineages were able to persevere through the event and radiate into a variety of new species. Among the survivors are burrowing snakes, who were able to find shelter underground, and those that lived in freshwater habitats.
The newly emptied environments then allowed snakes to specialise in a range of roles, such as marine snakes, as well as taking over from dinosaurs and other now-extinct predators to target small prey.
The snakes expanded into new areas of the world, including Asia.
Developments included the evolution of snakes which burrow. Image by Ltshears, licensed via Wikimedia Commons CC BY-SA 3.0.
The second extinction
Other subsequent large extinction events were also found to have impacted snake diversity. At the start of the Oligocene period 33.9 million years ago global temperatures dropped significantly, hitting cold-blooded animals like snakes.
The researchers suggest that the caenophidians, the group which contains about 80% of modern snakes, adapted to being active during the day around this time after their ancestors had been mostly nocturnal. This change allowed them to maximise the amount of heat gained from the Sun.
As the planet warmed over the following years, snakes could also move further north, allowing them to move to the Americas over the ancient land bridge that once linked Russia and Alaska.
However, while the research appears to correlate well with known events and other studies on snake diversity, the scientists faced a number of issues when assembling their model.
For instance, the snake fossil record is particularly patchy in places, especially in the period after the Cretaceous mass extinction event. It is also hard to identify the relationships between different snake fossil species as they often share homoplasies, which are characteristics that weren’t present in their ancestors, but have evolved separately.
To combat these issues, the researchers excluded some snake lineages whose classifications are controversial. They also used the timings of other groups, such as birds when radiated into a variety of species, to help calibrate the timeline of their snake family tree.
The researchers' work points to the importance of mass extinctions in producing the diversity of life as we know it today, particularly in the aftermath of the catastrophic Cretaceous mass extinction event.
