New snake discovery rewrites history, points to North America's role in snake evolution

A new species of fossil snake unearthed in Wyoming is rewriting our understanding of snake evolution. The discovery, based on four remarkably well-preserved specimens found curled together in a burrow, reveals a new species named Hibernophis breithaupti. This snake lived in North America 34 million years ago and sheds light on the origin and diversification of boas and pythons.

Hibernophis breithaupti has unique anatomical features, in part because the specimens are articulated -- meaning they were found all in one piece with the bones still arranged in the proper order -- which is unusual for fossil snakes.

Researchers believe it may be an early member of Booidea, a group that includes modern boas and pythons.

Modern boas are widespread in the Americas, but their early evolution is not well understood.These new and very complete fossils add important new information, in particular, on the evolution of small, burrowing boas known as rubber boas.

Traditionally, there has been much debate on the evolution of small burrowing boas.

Hibernophis breithaupti shows that northern and more central parts of North America might have been a key hub for their development.

The discovery of these snakes curled together also hints at the oldest potential evidence for a behavior familiar to us today -- hibernation in groups.

"Modern garter snakes are famous for gathering by the thousands to hibernate together in dens and burrows," says Michael Caldwell, a U of A paleontologist who co-led the research along with his former graduate student Jasmine Croghan, and collaborators from Australia and Brazil. "They do this to conserve heat through the effect created by the ball of hibernating animals. It's fascinating to see possible evidence of such social behavior or hibernation dating back 34 million years."

From Science Daily

Giant new snake species identified in the Amazon

A team of scientists on location with a film crew in the remote Amazon has uncovered a previously undocumented species of giant anaconda.

Professor Bryan Fry from The University of Queensland led a team which captured and studied several specimens of the newly named northern green anaconda (Eunectes akayima), located in the Bameno region of Baihuaeri Waorani Territory in the Ecuadorian Amazon.

"Our team received a rare invitation from the Waorani people to explore the region and collect samples from a population of anacondas, rumoured to be the largest in existence," Professor Fry said.

"The indigenous hunters took us into the jungle on a 10-day expedition to search for these snakes, which they consider sacred.

"We paddled canoes down the river system and were lucky enough to find several anacondas lurking in the shallows, lying in wait for prey.

"The size of these magnificent creatures was incredible -- one female anaconda we encountered measured an astounding 6.3 metres long.

"There are anecdotal reports from the Waorani people of other anacondas in the area measuring more than 7.5 metres long and weighing around 500 kilograms."

Professor Fry said the northern green anaconda species diverged from the southern green anaconda almost 10 million years ago, and they differ genetically by 5.5 per cent.

"It's quite significant -- to put it in perspective, humans differ from chimpanzees by only about 2 per cent," he said.

"This discovery is the highlight of my career."

The new anaconda species was found while filming with National Geographic for their upcoming Disney+ series Pole to Pole with Will Smith, on which Professor Fry, a National Geographic Explorer, was the expedition's scientific leader.

"Our journey into the heart of the Amazon, facilitated by the invitation of Waorani Chief Penti Baihua, was a true cross-cultural endeavour," he said.

"The importance of our Waorani collaborators is recognised with them being co-authors on the paper."

The scientists also set out to compare the genetics of the green anaconda with specimens collected elsewhere by world-leading anaconda expert Dr Jesus Rivas from New Mexico Highlands University, and use them as an indicator species for ecosystem health.

Professor Fry said the Amazon continues to face alarming ecological threats.

"Deforestation of the Amazon basin from agricultural expansion has resulted in an estimated 20-31 per cent habitat loss, which may impact up to 40 per cent of its forests by 2050," he said.

"Another increasing problem is habitat degradation from land fragmentation, led by industrialised agriculture and heavy metal pollution associated with spills from oil extraction activities.

"Forest fires, drought and climate change are also notable threats.

"These rare anacondas, and the other species that share this remote ecosystem, face significant challenges."

Professor Fry said his next research project would focus on heavy metal pollution in the Amazon.

"It's not only these gigantic snakes that are facing environmental threats, but almost all living things in the region," he said.

"The discovery of a new species of anaconda is exciting, but it is critical to highlight the urgent need to further research these threatened species and ecosystems.

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Flying snakes help scientists design new robots

Robots have been designed to move in ways that mimic animal movements, such as walking and swimming. Scientists are now considering how to design robots that mimic the gliding motion exhibited by flying snakes.

In Physics of Fluids, by AIP Publishing, researchers from the University of Virginia and Virginia Tech explored the lift production mechanism of flying snakes, which undulate side-to-side as they move from the tops of trees to the ground to escape predators or to move around quickly and efficiently. The undulation allows snakes to glide for long distances, as much as 25 meters from a 15-meter tower.

To understand how the undulations provide lift, the investigators developed a computational model derived from data obtained through high-speed video of flying snakes. A key component of this model is the cross-sectional shape of the snake's body, which resembles an elongated frisbee or flying disc.

The cross-sectional shape is essential for understanding how the snake can glide so far. In a frisbee, the spinning disc creates increased air pressure below the disc and suction on its top, lifting the disc into the air. To help create the same type of pressure differential across its body, the snake undulates side to side, producing a low-pressure region above its back and a high-pressure region beneath its belly. This lifts the snake and allows it to glide through the air.

"The snake's horizontal undulation creates a series of major vortex structures, including leading edge vortices, LEV, and trailing edge vortices, TEV," said author Haibo Dong of the University of Virginia. "The formation and development of the LEV on the dorsal, or back, surface of the snake body plays an important role in producing lift."

The LEVs form near the head and move back along the body. The investigators found that the LEVs hold for longer intervals at the curves in the snake's body before being shed. These curves form during the undulation and are key to understanding the lift mechanism.

The group considered several features, such as the angle of attack that the snake forms with the oncoming airflow and the frequency of its undulations, to determine which were important in producing glide. In their natural setting, flying snakes typically undulate at a frequency between 1-2 times per second. Surprisingly, the researchers found that more rapid undulation decreases aerodynamic performance.

"The general trend we see is that a frequency increase leads to an instability in the vortex structure, causing some vortex tubes to spin. The spinning vortex tubes tend to detach from the surface, leading to a decrease in lift," said Dong.

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Rising numbers of exotic snakebites reported in the UK

Exotic snakebites recorded in the UK have "soared" over the course of a decade, as numbers of the exotic pet increase -- a peer-reviewed study in Clinical Toxicologyreveals.

In 11-years, 300 patients with exotic snakebite were registered by the UK National Poisons Information Service (NPIS). This included 72 children aged 17 years or under and among those, 13 were aged just 5 years or less. No children had severe injuries.

Nine patients were bitten twice and one patient, some three times.

The new study, which included an audit of enquiries registered by the NPIS between 2009 and 2020 by experts from leading institutions across the UK, shows a total of 321 exotic snakebites from 68 different species.

Of those bitten, 15 had severe symptoms. This included a reptile conservationist who had previously survived a bite from an eastern green mamba but died after being bitten by a king cobra.

The World Health Organisation (WHO) considers more than 250 species of poisonous snake worldwide as medically important -- most native to Asia, Africa, Latin America and Oceania. But the possibility of encountering these dangerous species is no longer limited by geography. In recent years, snake ownership has increased in popularity in the UK. It is estimated that around one in 100 households now own a pet snake.

"The prospect of being bitten by an exotic (non-native) snake (in the UK) is still remote, with bites typically occurring in those keeping such snakes as part of their occupation or hobby," states lead author Pardeep Jagpal, from the National Poisons Information Service (Birmingham Unit). "Rapid access to expert clinical advice and the availability of appropriate anti-venom are important considerations when these accidents occur."

Advice to NHS healthcare professionals on managing exotic snakebites is available in the UK on a 24-hour basis through the NPIS. The authors examined all telephone calls involving snakebites that were received by the service between January 2009 and December 2020. They excluded enquiries about the European adder -- the only species of poisonous snake native to the UK -- or where the identity of the snake was unknown.

Of the 321 exotic snakebites in 300 patients:
 

• 207 (64.5%) of bites occurred in males -- and 10 people were bitten on more than one occasion.
• 72 (22.5%) of bites occurred in children -- 13 of whom were aged five or under.
• 184 (57.3%) of bites were inflicted by snakes of the family Colubridae, including hognose snakes, king snakes and false water cobras.
• 30 (9.3%) of bites were by Viperidae species, including western diamondback rattlesnakes and copperheads.
• 14 (4.3%) of bites were by Elapidae species -- most commonly by Indian cobras, monocled cobras and king cobras.

The majority of these exotic snakebites resulted in either no symptoms or mild to moderate symptoms. However, fifteen bites caused severe symptoms -- all of which were caused by front-fanged Viperidae or Elapidae. In total, seventeen people received antivenom treatment.

"Our results show an overall increase in the number of exotic snakebites reported to the NPIS compared to previous figures," says co-author the University of Oxford's Professor David Warrell, a world leading figure in tropical medicine, and the founding director of the Centre for Tropical Medicine and Wellcome Trust-Mahidol University Oxford Tropical Medicine Research Programme, Thailand.

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To keep up with evolving prey, rattlesnakes tap genetically diverse venom toolbox

In the evolutionary arms race between rattlesnakes and their prey, rodents, birds and other reptiles develop resistance to the snakes' deadly venom to survive. But new research led by the University of Colorado Boulder and University of Texas at Arlington sheds light on how snakes manage to keep the upper hand: They maintain a broad and diverse toolkit of genes that encode snake venom, allowing them to adapt as local prey and conditions change.

The findings, published today in Nature Ecology and Evolution, help explain how rattlesnakes have kept up with prey species evolving resistance to their venoms over millions of years. This research overturns decades of thought on what factors shape venom gene evolution and venom variation, and sheds new light on why developing effective antivenom treatments for snakebites remains so challenging.

"We found these rattlesnakes had a more diverse venom repertoire, more genetic tools in the toolkit, than their venom composition alone might suggest," said Drew Schield, lead author on the paper and postdoctoral fellow in Ecology and Evolutionary Biology at CU Boulder.

Snake venom, an evolutionary adaptation, is made up of different enzymes and toxins that enable snakes to capture their prey. For decades, biologists have thought that co-evolution between predator and prey would drive snake venom to become highly specialized: the venom evolving to effectively kill specific prey and unused venom gene genetic diversity disappearing along the way. Known in evolutionary biology as "directional selection" this process is like the sharpening of a knife -- while the weapon gets more deadly, it loses a bit of itself in the process.

The new study proposes that instead, "balancing selection" is the mechanism at play, an evolutionary process where multiple versions of a gene -- in this case, genes that encode venom proteins -- are maintained instead of eliminated. This could be the key to how snakes prevent themselves from going down evolutionary dead ends.

"The existence of these resistance mechanisms in prey led us to wonder: If there's selection pressure imposed back on the snakes, then it might make sense evolutionarily to have a more expanded venom arsenal," said Schield.

As rattlesnakes prey on a variety of animals, including mice, voles, birds and lizards, selection over time may not only maintain, but proactively select for a greater venom gene diversity, something no research has shown before.

"Our findings help explain decades of seemingly contradictory theory and evidence for what drives the extreme variation observed in snake venoms. It turns out that the arms-race between snakes and prey ends up favoring the constant re-shuffling of venom variants that are favored, leading to the retention of lots of venom variants over time, some of which are ancient," said Todd Castoe, co-author on the study and professor of biology at the University of Texas at Arlington.

Population level insights

During his work as a graduate student and postdoctoral researcher at the University of Texas at Arlington in 2019, Schield and his colleagues figured out where the venom genes reside in the rattlesnake genome, which up until that point was mostly a mystery. Now knowing the genetic architecture of venom as a trait (published in Genome Research), he realized scientists could investigate what evolutionary mechanisms have been operating on the venom genes.

Snake venom is a popular study subject, a promising model for understanding the origins of gene novelty. But previous studies in this field have not explored how selection has shaped this trait within closely related populations, so the researchers focused on select populations of rattlesnakes in Colorado, Montana, California and Idaho.

After scouting out locations where these snakes live, Schield and his co-authors traveled to a series of sites over several years in late spring and early summer from 2017 to 2020, where they collected 68 rattlesnakes belonging to two different species occupying the western United States in order to sample their blood, venom and take physical measurements.

They sequenced and analyzed genomes from these rattlesnake species, investigating genetic variation in regions of the genome housing venom genes. They found striking genetic diversity and strong evidence for natural selection maintaining multiple forms of different venom genes, adding to a growing body of evidence that balancing selection is more pervasive in nature than previously thought.

Based on the new study, Schield suspects that while directional selection may have driven the origins of venom, in more recent timescales, there may be an equilibrium shift towards balancing selection favoring diverse venom repertoires.

This may be one reason that snakebite is notoriously difficult to treat.

"These evolutionary mechanisms ramp up the complexity that you're contending with when you develop antivenoms, as venom composition within the same species but in different geographic regions might be totally different," said Schield.

Understanding how diverse venomous snake genomes truly are -- from rattlesnakes to cobras and coral snakes -- can inform advances in anti-venom therapeutics and save lives around the world, Schield said.

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Paleontologists debunk fossil thought to be missing link between lizards and first snakes

Filling in the links of the evolutionary chain with a fossil record of a ''snake with four legs" connecting lizards and early snakes would be a dream come true for paleontologists. But a specimen formerly thought to fit the bill is not the missing piece of the puzzle, according to a new Journal of Systematic Palaeontology study led by University of Alberta paleontologist Michael Caldwell.

"It has long been understood that snakes are members of a lineage of four-legged vertebrates that, as a result of evolutionary specializations, lost their limbs," said Caldwell, lead author of the study and professor in the departments of biological sciences and earth and atmospheric sciences.

"Somewhere in the fossil record of ancient snakes is an ancestral form that still had four legs. It has thus long been predicted that a snake with four legs would be found as a fossil."

Missing link discovered?

In a paper published in the journal Sciencein 2015, a team of researchers reported the discovery of what was believed to be an example of the first known four-legged snake fossil, an animal they named Tetrapodophis amplectus.

"If correctly interpreted based on the preserved anatomy, this would be a very important discovery," said Caldwell.

Caldwell explained that the new study of Tetrapodophis revealed a number of mischaracterizations of the anatomy and morphology of the specimen -- traits that initially seemed to be shared most closely with snakes, suggesting this might be the long-sought-after snake with four legs.

"There are many evolutionary questions that could be answered by finding a four-legged snake fossil, but only if it is the real deal. The major conclusion of our team is that Tetrapodophis amplectus is not in fact a snake and was misclassified," said Caldwell. "Rather, all aspects of its anatomy are consistent with the anatomy observed in a group of extinct marine lizards from the Cretaceous period known as dolichosaurs."

The clues to this conclusion, Caldwell noted, were hiding in the rock the fossil was extracted from.

"When the rock containing the specimen was split and it was discovered, the skeleton and skull ended up on opposite sides of the slab, with a natural mould preserving the shape of each on the opposite side," said Caldwell. "The original study only described the skull and overlooked the natural mould, which preserved several features that make it clear that Tetrapodophis did not have the skull of a snake -- not even of a primitive one."

A controversial specimen

Although Tetrapodophis may not be the snake with four legs that paleontologists prize, it still has much to teach us, said study coauthor Tiago Simões, a former U of A PhD student, Harvard post- doctoral fellow and Brazilian paleontologist, who pointed out some of the features that make it unique.

"One of the greatest challenges of studying Tetrapodophis is that it is one of the smallest fossil squamates ever found," said Simões. "It is comparable to the smallest squamates alive today that also have reduced limbs."

An additional challenge to studying the Tetrapodophis is access to the specimen itself.

"There were no appropriate permits for the specimen's original removal from Brazil and, since its original publication, it has been housed in a private collection with limited access to researchers. The situation was met with a large backlash from the scientific community," said Simões.

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Mammals on the menu: Snake dietary diversity exploded after mass extinction 66 million years ago

Modern snakes evolved from ancestors that lived side by side with the dinosaurs and that likely fed mainly on insects and lizards.

Then a miles-wide asteroid wiped out nearly all the dinosaurs and roughly three-quarters of the planet's plant and animal species 66 million years ago, setting the stage for the spectacular diversification of mammals and birds that followed in the early Cenozoic Era.

A new University of Michigan study shows that early snakes capitalized on that ecological opportunity and the smorgasbord that it presented, rapidly and repeatedly evolving novel dietary adaptations and prey preferences.

The study, which combines genetic evidence with ecological information extracted from preserved museum specimens, is scheduled for online publication Oct. 14 in the journal PLOS Biology.

"We found a major burst of snake dietary diversification after the dinosaur extinction -- species were evolving quickly and rapidly acquiring the ability to eat new types of prey," said study lead author Michael Grundler, who did the work for his doctoral dissertation at U-M and who is now a postdoctoral researcher at UCLA.

Mammals and birds, which were also diversifying in the wake of the extinction, began to appear in snake diets at that time. Specialized diets also emerged, such as snakes that feed only on slugs or snails, or snakes that eat only lizard eggs.

Similar outbursts of dietary diversification were also seen when snakes arrived in new places, as when they colonized the New World.

"What this suggests is that snakes are taking advantage of opportunities in ecosystems," said U-M evolutionary biologist and study co-author Daniel Rabosky, who was Grundler's doctoral adviser. "Sometimes those opportunities are created by extinctions and sometimes they are caused by an ancient snake dispersing to a new land mass."

Those repeated transformational shifts in dietary ecology were important drivers of what evolutionary biologists call adaptive radiation, the development of a variety of new forms adapted for different habitats and ways of life, according to Grundler and Rabosky.

Modern snakes are impressively diverse, with more than 3,700 species worldwide. And they display a stunning variety of diets, from tiny leaf-litter snakes that feed only on invertebrates such as ants and earthworms to giant constrictors like boas and pythons that eat mammals as big as antelope.

So, how did legless reptiles that can't chew come to be such important predators on land and sea? To find out, Grundler and Rabosky first assembled a dataset on the diets of 882 modern-day snake species.

The dataset includes more than 34,000 direct observations of snake diets, from published accounts of scientists' encounters with snakes in the field and from the analysis of the stomach contents of preserved museum specimens. Many of those specimens came from the U-M Museum of Zoology, home to the world's second-largest collection of reptiles and amphibians.

All species living today are descended from other species that lived in the past. But because snake fossils are rare, direct observation of the ancient ancestors of modern snakes -- and the evolutionary relationships among them -- is mostly hidden from view.

However, those relationships are preserved in the DNA of living snakes. Biologists can extract that genetic information and use it to construct family trees, which biologists call phylogenies.

Grundler and Rabosky merged their dietary dataset with previously published snake phylogenetic data in a new mathematical model that allowed them to infer what long-extinct snake species were like.

"You might think it would be impossible to know things about species that lived long ago and for which we have no fossil information," said Rabosky, an associate professor in the U-M Department of Ecology and Evolutionary Biology and an associate curator at the Museum of Zoology.

"But provided that we have information about evolutionary relationships and data about species that are now living, we can use these sophisticated models to estimate what their long-ago ancestors were like."

In addition to showing a major burst of snake dietary diversification following the demise of the dinosaurs in what's known as the K-Pg mass extinction, the new study revealed similar explosive dietary shifts when groups of snakes colonized new locations.

For example, some of the fastest rates of dietary change -- including an increase of roughly 200% for one subfamily -- occurred when the Colubroidea superfamily of snakes made it to the New World.

The colubroids account for most of the world's current snake diversity, with representatives found on every continent except Antarctica. They include all venomous snakes and most other familiar snakes; the group does not include boas, pythons and several obscure snakes such as blind snakes and pipe snakes.

Grundler and Rabosky also found a tremendous amount of variability in how fast snakes evolve new diets. Some groups, such as blind snakes, evolved more slowly and maintained similar diets -- mostly ants and termite larvae -- for tens of millions of years.

On the other extreme are the dipsadine snakes, a large subfamily of colubroid snakes that includes more than 700 species. Since arriving in the New World roughly 20 million years ago, they have experienced a sustained burst of dietary diversification, according to the new study.

The dipsadines include goo-eaters, false water cobras, forest flame snakes and hognose snakes. Many of them imitate deadly coral snakes to ward off predators and are known locally as false coral snakes.

"In a relatively short period of time, they've had species evolve to specialize on earthworms, on fishes, on frogs, on slugs, on snakelike eels -- even other snakes themselves," Grundlersaid.

"A lot of the stories of evolutionary success that make it into the textbooks -- such as Darwin's famous finches -- are nowhere near as impressive as some groups of snakes. The dipsadines of South and Central America have just exploded in all aspects of their diversity, and yet they are almost completely unknown outside the community of snake biologists."

Rabosky and Grundler stressed that their study could not have been done without the information gleaned from preserved museum specimens.

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