In a small office north of London, Stephanie Pierce from the Royal Veterinary College is watching a movement that hasn’t been seen for 360 million years. On her computer, she has resurrected the long-extinct Ichthyostega – one of the earliest four-legged animals to creep about on land. By recreating this iconic beast as a virtual skeleton, Pierce has shown that while it looked like a giant salamander, it couldn’t possibly have walked like one. It had some of the planet’s earliest bony legs, but they weren’t very good at taking steps.

Ichthyostega hails from the Devonian period, a time in Earth’s history when swimming transformed into walking. Fish invaded the land and evolved into the first tetrapods—four-limbed animals that include amphibians, reptiles, birds and mammals.  Muscular fins used for steering and balance evolved into legs for walking.

Since its discovery over 50 years ago, Ichthyostega has been an icon of this pivotal transition. Some 300 specimens have been found but many are incomplete, flattened or distorted. Pierce’s new model provides the best look yet at the animal’s skeleton. “It makes Ichthyostega a bit more tangible,” she says. “It’s not just a fossil laying in a rock now. It’s an animal that’s coming to life.”

Pierce built her virtual skeleton by putting dozens of Ichthyostega specimens in powerful CT-scanners, choosing only the best preserved ones out of the 300 or so in existence. “The front end of the animal was mainly composed from one beautifully preserved specimen called ‘Mr Magic’,” she says.

It was painstaking work. These fossils are so old that chemically, they are almost identical to the rocks around them. By eye, the bones stand out. To the scanners, they blend in. Pierce spent over two years scanning the specimens and building her model, but the results were worth it. “This has been on the wish-list for years,” says Michael Coates, who studies tetrapod evolution at the University of Chicago.

Those boots weren’t made for walking…

The model showed that Ichthyostega’s shoulders and hips were oddly restricted. They could move back and forth, and up and down, but they couldn’t rotate about their long axis. Hold your arm out and rotate your palm so it faces up then down—Ichthyostega’s shoulder couldn’t do that.

Most modern tetrapods need long-axis rotation in order to walk. Without it, their legs can’t be thrown forward or pulled backward. Ichthyostega’s limitations meant that despite having four limbs, it probably couldn’t have taken a step. It hind feet would never have been planted flat against the ground or supported its weight. It had invaded the land, but it wasn’t striding across it.

“It highlights the fact that the earliest tetrapods are not just ‘gigantic salamanders’, despite a vague similarity in outline,” says Per Ahlberg from Uppsala University. “The limbs and girdles are very different from anything now living.”

Pierce thinks that Ichthyostega moved by paddle with its front limbs, using powerful muscles and flexible elbows to make rowing motions. The closest living analogue is probably the mudskipper – a fish that drags itself along muddy land with its front fins (as in the video below).

Pierce also compared Ichthyostega’s joints and limbs to those of other living animals with sinuous bodies and interesting gaits, including a salamander, crocodile, seal, otter and platypus. Compared to these modern species, Ichthyostega’s hips and shoulders were similarly flexible in most planes of movements, but along their long axis, they could barely rotate.

Some scientists think that the tetrapods evolved limbs before they could walk, and their first members lived in shallow water. Others think that it’s the other way round, and that muscular limbs, hips and shoulders evolved while fish still had fins. The virtual Ichthyostega supports the former idea, since it had limbs but couldn’t walk. But Coates cautions against “fitting a smooth transition from swimmers to walkers.” He says, “Evolutionary transitions needn’t follow linear routes. Ichthyostega probably represents one of multiple experiments among the first tetrapods with limbs, trying-out life in the shallows.”

So… what made those tracks?

Other early tetrapods had similar shoulders and hips, so they probably had the same limitations too. John Hutchinson, who led the new study, plans to find out. His lab is busy reconstructing other early tetrapods including Acanthostega, one of Ichthyostega’s contemporaries, and Pederpes, a later model.

But Ahlberg notes that Ichthyostega had a very unusual and rigid spine, and may not have been representative of other early tetrapods. “Other tetrapods are known to have had more flexible spines” he says, “and this probably allowed them to overcome the limitations of their shoulders and hips”.

This might explain why Ahlberg and others have discovered tracks that pre-date Ichthyostega by around 20 million years, and had become fairly common by the time it evolved. Many of these tracks showed precisely the kind of salamander-like movements that Ichthyostega was apparently incapable of making. They were clearly made by early four-legged tetrapods, and to this date, we don’t know what made them.

Pierce agrees that the final word on Ichthyostega’s movements will have to wait until she can animate its entire skeleton. “The ultimate goal would be to try and create some sort of dynamic movement,” she says. She has applied for a grant to do just that, to model the motions of the entire animal, and compare them to salamanders or crocodiles. “That’s going to take so much time, but it’ll be very interesting,” she says.

PS: I want to point out that in researching this story, I spent a good minute on my living room floor trying to walk without long-axis rotation. It was really hard, and I looked like an idiot. I did a similar thing when I was writing about hummingbird wing movements for Nature. I’m going to christen this Method Science Journalism.

Reference: Pierce, Clack & Hutchinson. 2012. Three-dimensional limb joint mobility in the early tetrapod Ichthyostega. Nature http://dx.doi.org/10.1038/nature11124

Image by Julie Molnar

More on tetrapods:

Fossil tracks push back the invasion of land by 18 million years

Fish fins and mouse feet controlled by the same ancient genetic switch

The world’s largest animals have been hiding something. The bodies of the giant rorqual whales—including the blue, fin and humpback—have been regularly displayed in museums, filmed by documentary makers, and harpooned by hunters. Despite this attention, no one noticed the volleyball-sized sense organ at the tips of their lower jaws. Nicholas Pyenson from the Smithsonian Institution is the first, and he thinks that the whales use this structure to coordinate the planet’s biggest mouthfuls.

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Imagine a world of two dimensions, a world with no up or down… just across. No climbing, falling, jumping, or ducking… just shimmying and sidling. Welcome to the world of the sea skater.

Sea skaters, or ocean striders, are small bugs. They’re relatives of the pond skaters or water striders that zip spread-eagled across the surface of ponds and lakes. Except they skate over the open ocean, eating plankton at the surface. “They skate through storms and wind and waves,” says Miriam Goldstein from the University of California San Diego and the Deep Sea News blog. “They even have a little ‘life jacket’ – the hairs on their body trap air so if they get sunk by a wave, they pop back up. They’re amazing!”

There are only five species of sea skaters, all belonging to the Halobates group. Of all the millions of insect species, these five are the only ones to live out at sea. Now, Goldstein has discovered that one sea skater Halobates sericeus actually benefits from what most people would regard as an ecological disaster – the circling mass of plastic and debris known as the Great Pacific Garbage Patch.

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The worst sex you have ever had pales in comparison to what female water striders have to put up with. Put it this way: you have never been held down by your eyes.

As the female skates over the surface of ponds and lakes, males will try to force themselves upon her. She resists by struggling vigorously. But in some species, males can avoid being thrown off with antennae that have evolved into antler-shaped restraints. They bend in on themselves and are loaded with an array of prongs and spikes that perfectly fit to the shape of a female’s head.

Locke Rowe from the University of Toronto has been studying water striders for almost 20 years. In many species, males have evolved structures that give them an edge in their indelicate liaisons with females. “But the traits I studied before were rather simple – a spine here or there,” says Rowe. The subject of his latest study, a species called Rheumatobates rileyi – is… well, the opposite of simple.

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In the coastal waters of Laguna, Brazil, a shoal of mullet is in serious trouble. Two of the most intelligent species on the planet – humans and bottlenose dolphins – are conspiring to kill them. The dolphins drive the mullet towards the fishermen, who stand waist-deep in water holding nets. The humans cannot see the fish through the turbid water. They must wait for their accomplices.

As the fish approach, the dolphins signal to the humans by rolling at the surface, or slapping the water with their heads or tails. The nets are cast, and the mullet are snared. Some manage to escape, but in breaking formation, they are easy prey for the dolphins.

http://youtu.be/sVinWYmu5lQ

According to town records, this alliance began in 1847, and involves at least three generations of both humans and dolphins. Today, there are around 55 dolphins in the neighbourhood, and around 45 per cent of them interact with the fishermen.

Now, Fabio Daura-Jorge from the Federal University of Santa Catarina, Brazil studied Laguna’s dolphins to learn how their unusual collaboration has shaped their social networks. He spent two years taking photographs of the local dolphins, and noting where they travelled and who they were associated with. As is typical for bottlenose dolphins, the Laguna individuals formed a ‘fission-fusion’ society – they all belonged to the same large group, but they had specific ‘friends’ whom they would spend more time with.

The dolphins roughly split into two separate groups, based on their tendency to hunt with humans. Those that co-operated with the fishermen were more likely to spend time with each other than the uncooperative individuals. Likewise, the uncooperative dolphins showed a tendency to stick to their own clique.

One individual even seemed to act as a “social broker”, and spent time with individuals from both groups.

Of the two groups, the human-helpers seemed to form stronger social ties. It is not clear if helping humans means they spend more time together, or vice versa. But certainly, their close associations increase the odds that one dolphin will learn the hunting technique from its peers.

This fits with what we know about bottlenose dolphins. They are extremely intelligent animals and different populations have developed their own quirky foraging traditions by learning from one another. Some use sponges to guard their snouts when they root about the ocean floor for food. Others can prepare a cuttlefish meal by sequentially killing and stripping them.

Daura-Jorge now wants to understand why only some of the dolphins help the fishermen, given that doing so clearly provides them with benefits, and all of them have the opportunity to help. By analysing the dolphins’ genes, he hopes to piece together their family trees, and work out if mothers pass on the behaviour to their calves.

Reference: Daura-Jorge, Cantor, Ingram, Lusseau & Simoes-Lopes. 2012. The structure of a bottlenose dolphin society is coupled to a unique foraging cooperation with artisanal fishermen. Biology Letters http://dx.doi.org/10.1098/rsbl.2012.0174

Bonus: There are several cases around the world where dolphins feed on the discarded remains of fish thrown away by humans. But the Laguna animals do far more than that – the fisherman wouldn’t catch any fish at all without their help. A similar alliance takes place half a world away in Burma, where Irrawaddy dolphins also fish cooperatively with humans.

More on dolphin behaviour:

• Will we ever… talk to dolphins?
• When meeting up at sea, bottlenose dolphins exchange name-like whistles
• Dolphin detects electric fields with ex-whisker pits
• Dolphins stay alert after five straight days of round-the-clock vigilance
• How dolphins prepare the perfect cuttlefish meal
• Sponging dolphins keep it in the family
• Boto dolphins woo females with chat-up vines

The Amazonian tree known Hirtella physophora looks rather unassuming, but it is the site of several grisly spectacles. Amid its leaves and branches, an animal, a plant and a fungus conspire to create a nightmarish trap where trespassers become meals, robbers get the death penalty, and assassins are assassinated.

The tree is home to ants called Allomerus decemarticulatus, which defend it from hungry insects. In return, the tree provides the ants with leaf pouches and swollen thorns as shelter, and feeds them with nectar and sugary nodules. These food sources are rich in carbohydrates but low in proteins. To supplement their diets, the ants need flesh, and they get it by shaping the tree into traps.

The ants cut hairs from the plant and weave them together into a hollow gallery, which extends down the side of the tree’s branches. Within the gallery, the ants hide inside small holes, jaws agape. From the outside, nothing can see them. If an insect lands on the trap, hundreds of lurking jaws seize its legs and pull it spread-eagled, as if on a medieval ‘torture rack’. The victim is overpowered and dismembered.

http://www.youtube.com/watch?v=zrL5BYRqrTI

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In retrospect, the helmet should have been a clue…

Of all the super-senses that animals possess, the ability to sense the Earth’s magnetic field must be the most puzzling. We’ve known that birds can do it since the 1960s, but every new attempt to understand this ability – known as magnetoreception – just seems to complicate matters even further.

Take the latest discovery. Le-Qing Wu and David Dickman from the Baylor College of Medicine have found neurons in a pigeon’s brain that encode the properties of a magnetic field. They buzz in different ways depending on how strong the field is, and which direction it’s pointing in.

This is a big step. Scientists have identified parts of the brain that are important for magnetoreception, but no one has managed to nail down the actual neurons responsible for the sense. Miriam Liedvogel, who studies magnetic senses, calls it “a milestone in the field”.  It’s a key puzzle piece that has been unavailable for a very long time.

But Wu and Dickman’s discovery doesn’t solve the magnetoreception puzzle. If anything, it makes it more complex. Until recently, scientists thought that birds had two separate magnetic detectors – one in the eye and one in the beak. And it looks like the new magnetic neurons don’t hook up to either of these. “We can’t say where the signals come from,” says Dickman.

If these neurons are responding to magnetic fields, which part of the bird is feeding them their information? Is there a third sensor?

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On an uneventful day, five passers-by in busy Oxford shopping street suddenly stop and look upwards. They have spotted a camera mounted on a nearby roof, pointed straight at them. But these aren’t strangers who have suddenly realised that Big Brother is watching them. They are actors, who are taking part in a natural experiment that looks at how information spreads through crowds of people.

Andrew Gallup from Princeton University is behind the camera. Using its lens, and technology based on the video-gaming graphics cards, he can track the movement of each pedestrian, and calculate where they’re looking. With this set-up confirmed that people have a natural tendency to look where others are looking. But this contagion of glancing is much weaker than popular psychology books would have us believe.

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The sexual success of the male spotted bowerbird depends on his gardening skills. In his patch of forest, where he displays to mates, he cultivates a small fruiting shrub called the ‘bush tomato’, with purple flowers and green fruit.

It’s not clear if his actions are deliberate or inadvertent, but it is clear that he doesn’t eat the fruit. The plant is there to provide him with decorations, to make his boudoir that much more enticing to a female. Aside from humans, the spotted bowerbird is the only other animal that grows a plant for purposes other than food.

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For some scientists, an academic career can feel like crawling into a tower of crap. For other scientists, an academic career actually involves crawling into a tower of crap.

Since 1928, thousands of chimney swifts have roosted at Fleming Hall, a university building in Kingston, Ontario. For decades, they fed on local insects, and excreted the remains down one of the building’s chimneys. Around 2 centimetres of droppings, or ‘guano’, built up every year until the chimney was finally capped in 1992. To this date, Fleming Hall contains a hardened guano tower, two metres tall and 64 years in the making, which preserves a layered record of the swifts’ meals.

Now, a team of scientists, led by Joseph Nocera, have used this archive of historical poo to explain why the swift populations have fallen by 90 per cent since their heyday.

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