Humans do not act symmetrically. Most of us prefer, and are better at, using one hand rather than the other; balancing on one leg rather than the other; and for those of us who spin (gymnasts, dancers or divers, for example), spinning in one direction rather than the other.

Brains also do not function symmetrically. A version of this idea has long lived in pop psychology, where people are sometimes characterized as being either left-brained (analytical) or right-brained (creative). And although the pop-psych version of this may rest on questionable data, the underlying idea of asymmetrical brain function (what scientists call lateralization) is well-established. For example, in humans, language is typically processed in the left hemisphere, while spatial information is processed in the right.

Because each side of the brain controls a different side of the body, studying asymmetrical behaviors can provide us with information about asymmetrical brain function. And if we study this in animals, it may give us insights into brain evolution.

Handedness without hands

The type of lateralization most familiar to people is undoubtedly handedness. This has been studied in animals by looking at things like which hand monkeys use to grab something, which paw dogs use to knock food out of a container, and so on. But what do you do when the animal you're studying doesn't have hands (or paws)? How do you study lateralization in an animal like a dolphin?

It turns out that behavioral asymmetries come in various types, not just limb biases like handedness and footedness, but also sensory asymmetries, in which we do better on different types of tasks depending on which eye (or visual field) we use; and turning biases, where we prefer turning in one direction rather than the other.

Because different types of biases may come from different underlying causes, studying many different behavior types, across many different animals, can provide us with a fuller understanding of brain lateralization and its evolution.

A new spin on spinning

This is where it gets tricky. When comparing across animals, we have to take account of the fact that body plans and typical ways of moving may be different. For example, if the animal walks upright (like humans and birds) the long axis of its body is vertical, but if it walks on all fours, the long axis of its body is horizontal. This means that “turning” can involve very different types of movements. For an animal on all fours, turning involves crunching the long axis of its body to one side or the other. For an animal on two legs, turning involves spinning around the long axis of its body, which is kept straight. And for an animal like a dolphin who locomotes in three-dimensional space, either type of turning is possible.

When we set out to study lateralization in dolphins, we were careful to separate these two different types of turning, but we ran into another problem when our researchers kept disagreeing about what counts as a spin “to the right” (or left). After a lot of discussion (and sometimes argument), we realized that we had stumbled upon a weird quirk of human perception. Apparently, humans interpret the direction of spinning in opposite ways depending on the orientation of the animal.

To get a feel for this, try the following: First, stand up and spin “right.” Then lie down face-down on the floor and roll “right.” If you are like most people, in the upright case your right shoulder moved toward your back, while in the horizontal case your right shoulder moved toward your belly. That is, you made the exact opposite rotation. (And in case you’re wondering, no, you can't get around this by describing spins as clockwise/counterclockwise instead of right/left. You get the same results if you substitute “clockwise” for “right” in the examples above.)

Before this, almost all scientific studies of lateralization of turning or spinning motions had studied a single species in a single orientation, like a human turning (upright) or a whale breaching (horizontal)—so the issue had never come up. However, this meant that published research studies had in fact been using opposite coding systems for different animals, depending on their orientation. A spinning turn in which the animal’s right side moved towards its front was typically coded as left/ counterclockwise in studies of humans and walking birds, but as right/clockwise in studies of dolphins and whales. But of course, if we want to look at turning lateralization across different species, we all need to agree on the direction of a turn. This meant we needed a new coding system.

Remember that thing from physics class?

The system we came up with was actually inspired by the “right-hand rule” of electromagnetism that many of us learned in high-school or college physics. According to that rule, if you point your right thumb in the direction in which an electrical current flows through a wire, the curve of your fingers shows you the direction of the magnetic field flowing around that wire. We adopted the general outline of this schematic model to create the Right-Fingered Spin (RiFS) versus Left-Fingered Spin (LeFS) coding system. In this system, when a coder’s outstretched thumb is oriented along the animal’s long axis, pointed toward its head, the curled fingers of the relevant hand describe the direction of rotation. This allowed us to quickly and unambiguously code spinning/turning behaviors no matter the animal’s orientation or direction of movement.

So, what did we find?

Some previous scientific papers had claimed that dolphins show strong rightward behavioral asymmetries, similar to human right-handedness, and therefore had a left-hemisphere specialization for action. But since “right” didn't always mean the same thing in the earlier coding systems, it wasn’t clear if this claim was really true. To test it, we examined different types of behavioral asymmetries in a group of 26 dolphins, such as “Which direction do they swim around a lagoon?,” “Which side of their body do they touch things with?” and “Which direction do they spin if they dive up and to the side?” By making sure to separate out the different types of motion, and using the unambiguous RiFS/LeFS coding system, we found that—contrary to previous claims—dolphins do not have a general rightward asymmetry after all.

People often think that scientific progress happens when we learn something new that we didn't know before. But another kind of scientific progress happens when we realize that there is a problem with the way we’ve been looking at things all along. In those cases, figuring out a different way of looking can lead to seeing things more clearly. And as science fiction writer Isaac Asimov once pointed out, “The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka!’ but ‘That’s funny...’”

A wildlife expert has dismissed claims of a sighting of the extinct Tasmanian tiger, declaring the animals photographed were most likely pademelons.

Devotees of the extinct Tasmanian tiger, or thylacine, were abuzz this week with the potential new discovery that, if confirmed would have brought the animal back from the dead.

The Thylacine Awareness Group of Australia, an amateur not-for-profit organisation dedicated to the elusive creature, claimed it had photographic evidence of three thylacines living happily in north-east Tasmania.

In a video posted to YouTube, the group’s president, Neil Waters, said a camera trap had captured photos of a family of three thylacines, including a baby, which was “proof of breeding”.

But Nick Mooney, honorary curator of vertebrate zoology at the Tasmanian Museum and Art Gallery reviewed and assessed the material provided by Waters.

In a statement, TMAG said Mooney had “concluded that based on the physical characteristics shown in the photos provided, the animals are very unlikely to be thylacines, and most likely Tasmanian pademelons”.

“TMAG regularly receives requests for verification from members of the public who hope that the thylacine is still with us. However, sadly there have been no confirmed sightings documented of the thylacine since 1936.”

The thylacine is believed to have been extinct since 1936, when the last living thylacine, Benjamin, died in Hobart zoo. But unconfirmed sightings have regularly been reported for decades.

In 2017, scientists from James Cook University in Queensland also conducted a search for the marsupial after multiple “plausible” sightings.

A 2019 document from Tasmania’s Department of Primary Industries, Parks, Water and Environment revealed there had been eight claimed sightings of the thylacine between 2016 and 2019.

Forrest Galante, an American television host with the Animal Planet channel, added to the earlier hype when he shared the video about the potential “wildlife rediscovery of the century” on Twitter.

Mooney’s conclusion will come as a blow to thylacine enthusiasts who were convinced they finally had the evidence they needed.

In his announcement video, Waters said he and the “committee” of the thylacine group had discovered the photographs from a camera in north-east Tasmania.

“The last 10 days, I’ve probably been acting a bit weird to everybody in the group and online,” Waters said. “That’s because when I was checking the SD cards I found some photos that were pretty damn good.

“We believe that the first image is the mum, we know the second image is the baby, because it’s so tiny, and the third image is the dad.”

Waters said the picture of the supposed mother and father “are ambiguous”, but that the baby was definitely a thylacine.

“The baby is not ambiguous, the baby has stripes, a stiff tail, the hock, the coarse hair, it’s the right colour, it’s a quadruped, stocky, and it’s got the right shaped ears,” he said.

“Looking at the baby, not only we do we have a family walking through the bush but we have proof of breeding.”

Waters said this would put the “thylacine in a much stronger position than it’s been in for the last 30-something years” – referring to the 1990s for some reason.

He signed off: “Congratulations everyone. We’ve done it, cheers!”

Waters told Guardian Australia in 2016 that he saw a thylacine in 2014 when he was doing work on his house and it walked past his bedroom window.

In 2018, two people from Western Australia reported seeing a thylacine while visiting Tasmania, according to the state environment department’s report.

“The animal walked from the right hand side of the road … turned and looked at the vehicle a couple of times,” it said. “It was in clear view for 12-15 seconds.

“The animal had a stiff and firm tail, that was thick at the base. It had stripes down its back. It was the size of a large Kelpie (bigger than a fox, smaller than a German shepherd).

“The animal was calm and did not act scared at all. Both are 100% certain that the animal they saw was a thylacine. It appeared to be in good condition.”

Decompression sickness, or the bends, is a threat humans face if we ascend too swiftly from the ocean’s depths. If divers don’t take proper care when returning to the surface, dissolved gases can enter their joints, skin, and brain, forming damaging bubbles—sometimes with lethal consequences. But decompression sickness is not restricted to people, nor, as it turns out, is it a new problem. A recent analysis of the fossil record reveals that even prehistoric sea monsters were laid low by bubbles.

Bruce Rothschild, a physician based at Northeast Ohio Medical University, moonlights as a paleopathologist, investigating the effects of disease on ancient animals. While studying fossilized vertebrae of the mosasaur Platecarpus—a four-meter-long marine reptile that lived around 84 million years ago—for signs of infection, he and his colleagues sliced open the bone to examine the internal architecture. What they found surprised him: a strip of dead tissue in an otherwise healthy bone.

The diagnosis was avascular bone necrosis. Something had blocked the blood flow to the tissue, which killed the cells. The same condition can affect bends-stricken divers when gas bubbles block the flow of blood. After ruling out other potential causes for the dead tissue, such as bismuth poisoning and radiation damage, Rothschild concluded that decompression sickness was the only explanation that made sense.

Soon enough, Rothschild was finding bone necrosis in all sorts of prehistoric reptiles. Snake-necked plesiosaurs and fish-like ichthyosaurs, for instance, had the same symptoms. But mosasaurs were the most affected.

“Avascular necrosis was universal in half a dozen genera of mosasaurs, and it didn’t matter whether they came from Alabama or Belgium,” Rothschild says.

The reason why these ancient reptiles, otherwise so well adapted to underwater life, succumbed to the bends was a mystery.

Paul Jepson, a veterinarian at the Zoological Society of London, says that decompression sickness was widespread in the fossil record of ancestral marine animals but became less prevalent as time went on. Perhaps reptiles just needed time to evolve out of this affliction, he says.

Yet the bends has not vanished completely. The condition is rarely seen in modern reptiles, but the most conclusive cases come from turtles. In 2014, Daniel García Párraga, a veterinarian at Oceanogràfic, an aquarium in Valencia, Spain, documented the first known cases of the bends in loggerhead turtles, in a paper coauthored by Jepson. Out of 67 turtles brought into García Párraga’s surgery after having been accidentally caught by local fishermen, 29 showed signs of decompression sickness.

That there is evidence for the bends in both ancient and modern reptiles, yet few known cases in mammals, prompted Agnete Carlsen, a medical doctor working with the Natural History Museum of Denmark, to suggest a possible explanation: a flaw in the reptilian heart that predisposes it to decompression sickness.

“In the reptile heart, there is a connection between the right and the left heart chambers,” Carlsen explains. When an animal dives, blood is shunted from right to left; during fast decompression, this allows bubbles to cross the arterial circuit and cause damage.

People born with a reptile-like opening between their heart chambers face the same problem. That disorder, called patent foramen ovale, is unlikely to cause serious health problems on land, but makes people far more susceptible to decompression sickness.

If prehistoric marine reptiles had hearts like modern turtles—something that can be inferred from their place in the reptile family tree—this could explain the prevalence of decompression sickness in the fossil record.

That said, the decompression sickness in the turtles García Párraga examined likely had more to do with them being dragged up in fishing nets than the susceptibility of their prehistoric hearts.