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Whales used to walk on land

A. Gennari

By Michael Le Page

A fossil of a 43-million-year-old whale that was still able to walk on land on four legs has been found in Peru. It is the first amphibious whale found in the southern hemisphere, and suggests that whales managed to swim across the South Atlantic early in their evolution.

The 3-metre-long animal looked a bit like an otter or a beaver, with four legs and a large tail for swimming.

“It was still capable of bearing its weight on its limbs,” says Olivier Lambert at the Royal Belgian Institute of Natural Sciences, a member of the team that made the discovery. “It was intermediate between fully walking and fully aquatic.”

Whales started evolving in South Asia around 50 million years ago, from a dog-like creature related to deer and hippos. As they became more aquatic, these early whales began spreading along coasts.

Fossils of semi-aquatic whales have recently been found in West Africa. The latest discovery suggests that these early whales managed to swim from there to South America at least 43 million years ago.

At the time, the West African coast was just 1200 kilometres from what is now Brazil, and there was a westward current. But it would still have taken a week or two to make the crossing. That may suggest that these whales were already capable of surviving without fresh water, and of sleeping at sea.

They soon reached North America too, where fossil teeth dating to around 41 million years ago have been found.

The last common ancestor of all modern whales and dolphins lived 37 million years ago, so the new discovery may be one of the ancestors of modern whales. However, it is far more likely to be a cousin – a member of a side branch that died off, says Lambert.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2019.02.050

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CRISPR has been used to make albino brown anole lizards

Doug Menke

By Michael Le Page

The CRISPR genome-editing technique has been used to make the world’s first genetically modified reptiles: four albino lizards. The breakthrough may have a wide variety of uses, from studying human eye disorders to tackling invasive pythons.

Our ability to tweak the genomes of animals like mice and zebrafish has been hugely useful for medical research. But there are some conditions that are hard to study in existing lab animals. For instance, people with albinism often have vision problems because the genetic variants that …

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For millions of years, Earth has provided water, oxygen and the key elements required by life

Kacper Kowalski/Panos Pictures

By Bob Holmes

IN 1948, cybernetics pioneer Ross Ashby built a curious machine. The Homeostat was constructed from four interconnected bomb-control units scavenged from the UK’s Royal Air Force. It featured four pivoting magnets, the position of each being determined by that of the others and guided by feedback mechanisms generated using a table of random settings. When Ashby turned the machine on, the magnets would start to oscillate wildly. Sometimes they would return to a stable equilibrium position. If not, Ashby had wired the Homeostat to reboot itself with a new selection of random settings. Over time, this basic algorithm – if unstable, try again – always eventually led to equilibrium. That was the machine’s sole purpose: to show that a simple, dynamic system would regain stability in response to changes in its environment.

Ashby believed this “ultrastability” to be a governing principle in nature, explaining, among other things, the adaptation of species to their niche – a process that appears purposeful, but actually arises from random processes. It may seem a stretch to describe the Homeostat’s change over time, from wild motion to stability, as “evolution”. After all, it lacks all the trappings we associate with Darwinian evolution – such as life and reproduction. Yet, there is a growing belief that the same forces driving Ashby’s machine hold the key to a wider concept of evolution, one that can encompass semi-living and even nonliving systems. This new view may prove essential to understanding the functioning of ecosystems and even the origin of life. Most intriguingly, it bolsters …

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The warty comb jelly has an anus like no other

imageBROKER / Alamy Stock Photo

By Michael Le Page

A jellyfish-like creature has a neat trick that makes it unique among animals: its anus forms only when it needs to defecate, then disappears without a trace.

“That is the really spectacular finding here,” says Sidney Tamm of the Marine Biological Laboratory in Woods Hole, Massachusetts, who made the discovery. “There is no documentation of a transient anus in any other animals that I know of.”

Tamm thinks the discovery might represent an intermediate stage in evolution.

In some simple animals, such as jellyfish, the gut has only one opening, which functions as the mouth and anus.

It has been known since 1850 that comb jellies – which superficially resemble jellyfish, but belong to a separate group called ctenophoreshave a through-gut, with a separate mouth and anus. Some even have more than one anus.

Missing anus

But when Tamm studied the warty comb jelly (Mnemiopsis leidyi), he could not find its anus. Only when the animals are actually defecating does a tiny opening appear – and it disappears again straight afterwards.

“It is not visible when the animal is not pooping,” says Tamm. “There’s no trace under the microscope. It’s invisible to me.”

His observations show there is no permanent connection between the gut and the rear of the body. Instead, as waste accumulates, part of the gut starts to balloon out until it touches the outer layer, or epidermis.

The gut then fuses with the epidermis, forming an anal opening. Once excretion is complete, the process is reversed and the anus vanishes.

Because both the gut and epidermis are just a single cell layer thick, this can happen relatively easily and quickly. The animals defecate at regular intervals: once an hour in the 5-centimetre-long adults, and once every 10 minutes or so in the larvae.

Tamm thinks this process of the gut bulging and fusing with the epidermis to form an anus is how the anus evolved in the first place. The intermittent anus may represent an intermediate stage in which the structure has yet to become permanent.

Today, the transient anus may be unique to the warty comb jelly. Tamm is now looking at other species of comb jelly, but so far they appear to have permanent anuses.

Journal reference: Invertebrate Biology, DOI: 10.1111/ivb.12236

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“How did I get my stripes? It’s a long story…”

Tim Caro/UC Davis

By Michael Marshall

When it comes to explaining why zebras have stripes, it’s best to remember that some issues are not black and white.

Biologists have been debating the puzzle since Darwin’s time, but a study published on Wednesday offers further evidence for one of the most promising explanations: that the stripes deter biting flies.

In the parts of Africa where zebras live, there are blood-sucking horseflies that carry lethal diseases such as trypanosomiasis. Clearly, zebras would do well to avoid being bitten. The idea is that the stripes somehow confuse the flies so that they don’t land on the zebras.

A team led by Tim Caro of the University of California, Davis tracked captive zebras and horses at a site in England. Horseflies circled round both, but they landed on horses significantly more often. Putting striped coats on the horses’ bodies meant the horseflies landed there less often – but still landed on their heads, which were uncovered. The implication is that the stripes were having a real effect.

The hypothesis backed by a lot of evidence, but does that mean it’s the only reason for a zebra’s stripes? Not necessarily. Some ideas don’t seem to stand up, notably the suggestion that the stripes help zebras cool down on hot days – if that were true, we would expect a lot more tropical animals to be stripy. But other ideas seem to have more to them.

Dazzle camouflage

One which at first seems ridiculous is that the stripes are a form of camouflage. Obviously, zebras are not inconspicuous. But the stripes could create “dazzle camouflage”: overwhelming the predator’s visual system and making it hard to track the zebra’s movement. Think about the experience of watching a herd of zebras all dashing in different directions, and imagine trying to pick out one of them to bring down.

The evidence here is mixed. A 2016 study suggested that the dazzle effect only really works if the stripes are parallel to the animal’s direction of travel, implying that zebra stripes don’t work this way. But this was based on tracking humans playing a computer game. A 2014 study, based on computer modelling of how moving zebras would appear to a predator, suggested that the stripes would be extremely confusing.

There is also the simple possibility that the stripes are a signal. The message may not be for other zebras: in 2017, researchers suggested that the stripes signal to other grazing animals, encouraging them to graze alongside the zebras. Such mixed-species herds offer more protection against predators. For now this is only a hypothesis.

Perhaps the most important point is that these studies can only tell us is why zebra stripes continue to exist today, not why they arose in the first place. Evolution is good at re-purposing things, so a body part may arise, be used for one purpose, and then end up being used for something entirely different.

An obvious example is the lens of the mammalian eye, which probably arose simply as a protective cover for the retina and only later developed the ability to focus light, creating a sharper image – which is now its most “obvious” function. It may be that zebra stripes have a similarly complex history.

There is something psychologically appealing about a single, clear explanation. That instinct doesn’t mean we are wrong to seek such things – sometimes just-so stories turn out to be correct – but this is one area where our biases can work against us.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0210831

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The world’s oldest burrows?

Abderrazak El Albani

By Michael Le Page

Burrow-like structures several millimetres in diameter have been found in 2.1-billion-year-old rocks in Gabon, Africa. The structures were made by a moving lifeform of some kind, claim geologist Abderrazak El Albani at the University of Poitiers in France and his team.

The team do not know what made the trace fossils, but they speculate that it could be something similar to colonial amoeba or slime moulds – organisms made of cells that normally live separately. The trace fossils were found near bacterial mats that the mysterious lifeforms may have been feeding on. “It’s truly amazing,” says El Albani.

Previously, the earliest evidence of moving lifeforms was just a half a billion years old. There are burrows and tiny footprints in rocks of this age, probably left by small animals.

The 2.1-billion year-old burrows are very unlikely to have been produced by organisms as complex as animals, which probably appeared only between about 850 and 650 million years ago. In fact, it’s not even clear that organisms as complex as amoeba were around 2.1 billion years ago: they are eukaryotes, and the oldest eukaryotic fossils found so far are about 1.7 billion years old. So if El Albani’s interpretation is correct, these finds challenge the conventional story of life’s evolution.

Multicellular organisms

On the other hand, it’s clear that multicellularity evolved on numerous different occasions. There are even multicellular organisms composed of simple – prokaryotic – cells. And lab experiments suggest it’s relatively easy for cells to evolve multicellularity.

In 2010, El Albani reporting finding what his team think are fossils of multicellular organisms in the same sedimentary rocks in the Franceville basin in Gabon, which formed in a warm, shallow ocean 2.1 billion years ago. “It’s a unique place in the world, where we have this preservation of the rocks,” he says. Most rocks are of this age have been metamorphosed by extreme heat and pressure.

Since then, his team have continued to make field trips and have collected more than 500 specimens – now including the apparent trace fossils. These organisms lived at the time when oxygen levels were relatively high, says El Albani.

Shortly after oxygen level plummeted and remained low for a billion years – the “Boring Billion”. So El Albani thinks complex lifeforms started to evolve much earlier than thought, but were then killed off. “These organisms disappeared,” he says.

But Nicholas Butterfield of the University of Cambridge is sceptical about the team’s new interpretations. “It’s such an extraordinary claim,” he says. “But they don’t give compelling data to support it.”

Journal reference: PNAS, DOI: 10.1073/pnas.1815721116

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We may have to rethink how kangaroos came to hop

Peter Shouten/Australian Geographic

By Sam Wong

An ancient group of kangaroo relatives called balbarids had multiple ways of getting around, including hopping, bounding and climbing. The finding may mean we have to rethink how modern day kangaroos came to hop.

Kangaroo evolution has been difficult to piece together because there are very few fossils older than one or two million years. The prevailing view of kangaroo evolution is that they began hopping when the climate in Australia became drier and wiped out many forests, but new fossil evidence suggests that their relatives were hopping much earlier.

The balbarids were distant cousins of modern kangaroos and lived in forests when the Australian climate was wetter. They went extinct around 10 to 15 million years ago when the climate dried out.

One of the most complete skeletons, from a species in the balbarid family called Nambaroo gillespieae, suggests that these animals moved on four legs and did not hop like true kangaroos.

Benjamin Kear at Uppsala University, Sweden, and colleagues have now analysed a set of more fragmentary remains, including ankle bones, a calf bone and a claw. They suggest that some balbarids galloped, some hopped, and some climbed in trees.

The fossil bones were found in Riversleigh in northeastern Australia

Benjamin Kear

That’s true of modern kangaroos too, if you look beyond the most famous among them. There are rat kangaroos that scurry in the undergrowth and burrow, and tree kangaroos that live in the forests of New Guinea. Short-faced giant kangaroos, which went extinct 30,000 years ago, walked on two legs like us.

This versatility has been key to kangaroos’ success, enabling them to exploit a huge range of terrestrial environments, says Kear. The origin of hopping goes all the way back to virtually the beginning of kangaroo evolution, he says.

That means we have to rethink how and when kangaroos came to hop. “Hopping didn’t evolve with the climate; hopping was already there and took advantage of environmental change when it occurred,” says Kear.

Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.181617

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By Colin Barras

BIOLOGY is a messy business. Witness these sage words: “It is really laughable to see what different ideas are prominent in various naturalists minds, when they speak of ‘species’… It all comes, I believe, from trying to define the undefinable.”

Strong stuff. And from a surprising source. Charles Darwin wrote those lines in a letter to fellow naturalist Joseph Hooker, just three years before the publication of On the Origin of Species. Darwin clearly had a problem with the word to which his name is now so intimately linked. It turns out he is not alone. Today, almost 160 years after he revolutionised biology, how to define a species is more problematic than ever.

You probably learned that a species is a group of individuals that can breed to produce fertile offspring, but this is just one of dozens of competing definitions. The lack of consensus on what a species is has big implications for how we think about the natural world and for our efforts to conserve it. But the problems go even deeper. Recent revelations about interbreeding between what some regard as separate species of ancient humans have left many of us wondering: who are “we”, who are “they” and are we actually all one and the same? In other words, how we define a species has become a question at the very heart of human identity. Perhaps it is time to rethink the whole concept.

The idea that the living world is divided into distinct species has deep roots. Frank Zachos at the Natural History Museum Vienna, Austria, suspects it predates the written …

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DIVIDE and conquer! This isn’t just a political or military strategy, it is a human imperative. Categorising is in our nature. It is how we make sense of the world, from personal identity to scientific investigation. But sometimes, something happens that illuminates the arbitrariness of our classifications – something like the discovery that our species, Homo sapiens, contains DNA from Neanderthals.

Most of us think of a species as a group of individuals that can interbreed to produce fertile offspring. In which case, either humans are hybrids or we have been mistaken in seeing Neanderthals as “other”. In fact, it isn’t that simple. This definition is just one of 34, all of which are valid ways of categorising the living world, depending on your viewpoint (see “Human or hybrid? The big debate over what a species really is”).

This taxonomic confusion goes far beyond human identity to the heart of how we value nature: using an alternative definition can instantaneously transform one species into several – or reclassify an endangered species as a hybrid. One solution is to ditch the idea of “species” altogether. Whatever would Darwin think?

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The oldest known animal looked like modern sea gooseberries

Ron Offermans, Buiten-beeld/FLPA

By Graham Lawton

MOVE over, Dickinsonia. This 558-million-year-old creature was named the earliest known animal last year, but New Scientist can now exclusively reveal one that existed even earlier – by more than 40 million years.

This previously unknown animal comes from 600-million-year-old rocks in China and doesn’t have a name yet. While Dickinsonia was an Ediacaran – a primitive group of organisms that went extinct about 541 million years ago – the unnamed animal seems to have belonged to a group of animals that still exists today: comb jellies. …

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