Dinosaurs are the biggest creatures to have ever walked on land, dominating Earth for over 130 million years. But how could such extraordinary creatures have simply vanished in the blink of a geological eye? For decades, we’ve assumed these prehistoric megafauna 鈥� a staple of our childhoods and Hollywood movies 鈥� went extinct for one simple reason: the asteroid that hit Earth was so unimaginably large that it changed everything in one single blow. But now, thanks to new research, an even more intriguing idea has emerged: size alone doesn’t explain what happened.

The real reason the impact was so devastating may have been its angle. Had the asteroid arrived a little steeper, the outcome might have been different. A little shallower, different again. And for life on Earth at the time, predominantly dinosaurs on land, marine creatures in the sea and pterosaurs in the air, it appears to have struck at almost the worst possible angle imaginable, launching vast quantities of rock, dust and climate-altering gases high into the atmosphere and triggering one of the greatest mass extinctions in Earth’s history.

A 555-million-year-old worm had a predilection for turning right, possibly indicating the oldest known example of handedness.

Although these worms lacked limbs and so couldn鈥檛 be considered left- or right-handed in the way that we understand, the development of a tendency to favour one side over another is evidence of an advanced nervous system.

It remains a feature of free-living mobile life today, but until this discovery, it wasn鈥檛 thought to have emerged until the Cambrian Period, which began around 541 million years ago.

at the American Museum of Natural History in New York and his colleagues analysed 100 fossil specimens of a small flatworm-like creature, Spriggina floundersi, collected in South Australia over recent decades.

These animals lived during the Ediacaran Period, when multicellular life first became widespread. It preceded the Cambrian explosion, when animal life diversified dramatically and many groups of animals first appeared.

Spriggina lived in what was, half a billion years ago, a shallow ocean and is thought to have foraged on or close to the seafloor, moving by wriggling to the left or right.

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鈥淲e have around 50 specimens of Spriggina that are clearly bent,鈥� says Evans. Twice as many of the fossilised worms are bent to the left than to the right, he says. This means the creature itself bent to the right, as the specimens are mirror-image impressions of the animals, made when storms buried them in sand.

鈥淭his appears to be statistically significant and matches what biologists find when they study handedness in different animals today,鈥� says Evans. 鈥淪ome specimens have multiple bends to both the right and left, suggesting that they all could bend both ways, which makes sense if you don鈥檛 want to be stuck moving in a circle.鈥�

While the majority seem to demonstrate right-handedness, it is hard to tell if any were left-handed, he says. 鈥淚 imagine it鈥檚 like taking a picture of 100 people waving with one hand today. You would likely be able to count that more people are waving with their right hand, but you wouldn鈥檛 be able to tell who is right- or left-handed.鈥�

Discoveries like this demonstrate that many foundational characteristics that are common to a variety of animals today, such as the ability to move around, bilateral symmetry and handedness, evolved in the Ediacaran, says Evans.

In the Cambrian, organisms built on that foundation to become more complex, for example adding legs to move more efficiently, becoming 鈥渓ess alien and more like the major groups of animals we know today鈥�, says Evans. 鈥淭his is cool because it suggests that, while the Cambrian was an amazing time in animal evolution, those organisms didn鈥檛 just come out of nowhere: they built on the foundations established in the Ediacaran.鈥�

鈥淭he presence of handedness in any kind of functional asymmetry, really deep into the fossil record, gives us important and interesting information about how these behaviours have evolved and how deeply in time they emerged,鈥� says at Flinders University in Adelaide, Australia.

A wide variety of fruits and seeds that were smothered in the ash from a volcanic eruption nearly 75 million years ago suggest flowering plants were diverse and thriving in the time of the dinosaurs, far earlier than previously known.

Researchers had thought the emergence of large seeds and fruits followed the end-Cretaceous extinction, 66 million years ago, and was tied to the rise of mammals and birds.

鈥淣ow, we have evidence that large fruit and seeds and the related ecological conditions can be traced back to 10 million years before the asteroid impact that wiped out the dinosaurs,鈥� says at the University of California, Berkeley.

Lee and his colleagues analysed ancient fossils collected from the Jose Creek Formation in New Mexico over the past three decades. They are so well preserved because, like the Roman city of Pompeii, the plant fossils were locked within a bed of ash from a volcanic eruption.

The team discovered an extraordinary 77 different kinds of fruits and seeds. Such a ready banquet of nutritious fruit would almost certainly have been eaten by herbivorous dinosaurs and other animals.

The findings show flowering plants that enclose their seeds in fruit, also known as angiosperms, were co-evolving with the animals that fed on them as a way of dispersing their seeds.

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鈥淲hile many Mesozoic animals, like dinosaurs, birds, pterosaurs and mammals, were suggested to have consumed angiosperm diaspores, we didn鈥檛 have the botanical evidence supporting this,鈥� says Lee. 鈥淣ow we have.鈥�

The first flowering plants emerge in the fossil record 136 million years ago, but, until now, it was thought early forms were mostly small and weedy and vastly different to the range of species that dominate Earth鈥檚 forests today.

In Cretaceous deposits elsewhere, the fruit and seeds are roughly the size of a poppy seed on average 鈥� far smaller than the blueberry-sized seeds at Jose Creek.

Of the 77 new types of seeds identified by the scientists, nearly a third are classified as fleshy while only 5 per cent are winged, which would imply dispersal by wind rather than animals.

Alongside the flowering plants, the tropical forest also contained several kinds of conifers, including a redwood relative, as well as palms.

While many of the seed shapes are familiar to us today, the forest structure would have been extremely different and unfamiliar, says team member , also at the University of California, Berkeley.

The larger fossils can be compared to blueberries and large acorns in size, she says. 鈥淲e don鈥檛 have a good idea which plant group produced these; for that, you have to find them attached to shoots with leaves,鈥� says Looy. 鈥淗owever, when they are fleshy they are likely dispersed by larger herbivores.鈥�

A set of exquisitely preserved 300-million-year-old fossils suggests that early four-limbed vertebrates did not undergo a metamorphosis between their juvenile and adult stages, challenging conventional ideas about the evolution of life on land.

鈥淲e have for a very long time assumed that these animals were broadly amphibian-like, and that this life cycle would have bridged the gap between life in the water and life on land,鈥� says at the Field Museum of Natural History in Chicago.

Today鈥檚 reptiles, birds, mammals and amphibians belong to a group called tetrapods, which evolved from lobe-finned fish around 390 million years ago. But almost nothing was known about the early developmental stages of these ancestral lobe-finned fish, says at Flinders University in Adelaide, Australia.

Pardo and his colleague , also at the Field Museum, examined a collection of fossils that were unearthed between the 1960s and 1990s at the Mazon Creek fossil site, south-west of Chicago. The preserved animals lived 307 million to 309 million years ago, during the Carboniferous Period.

Embolomeres, which had a body around 2 metres long in adulthood, were the largest tetrapods in the Carboniferous and one of the top predators. They spent most of their time in water, but had small legs with which they could have clambered onto the land.

The fossils included two 2-centimetre-long baby embolomeres, which were so well preserved that the scientists could see soft tissues and even egg yolk.

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In tadpoles, the yolk sac remains inside the body for a few days after hatching as a store of energy. But the young embolomeres had a yolk sac outside the body, similar to the case for some young fish such as lungfish.

Amphibian larvae, such as tadpoles, have external gills that enable them to breathe underwater, but the young embolomeres did not. 鈥淭he absence of external gills across early development in these animals is the smoking gun,鈥� says Pardo.

The skull and skeleton have 鈥渁ll the important parts seen in an adult embolomere鈥�, says Pardo. The fossils show that embolomeres remained more or less the same from the time they hatched from their eggs until they reached adulthood.

鈥淗uman bodies basically work the same way from birth through adulthood, but we get bigger and our proportions change, but we don鈥檛 undergo the sort of fast, rapid change you see in a frog or salamander,鈥� says Pardo. 鈥淥ur fossils show that this sort of life cycle was the norm for our earliest terrestrial ancestors, too.鈥�

Although embolomeres were aquatic, Pardo argues that the evidence available suggests our earliest terrestrial ancestors did not have a tadpole-like stage either. The team also studied the fossil remains of two other early tetrapod species that were alive at the same time and in the same place as the embolomeres.

鈥淣one of these show any evidence of a tadpole-like stage,鈥� says Pardo. 鈥淣either do other fishy tetrapod relatives such as early lungfishes and coelacanths. So is it impossible that a tadpole stage showed up somewhere and was subsequently lost? Maybe, but it seems vanishingly unlikely with the data we have.鈥�

This study fills in a much-needed knowledge gap, says Long. 鈥淚t shows how early tetrapod-like fishes living about 308 million years ago did not need to develop a tadpole phase in order to invade land, as was previously thought by some scientists.鈥�

Fossil hunting in the Australian outback

Join this extraordinary adventure through the heart of Australia鈥檚 fossil frontier. Once a shallow inland sea millions of years ago, eastern Australia is now a hotspot for fossils. Over 13 unforgettable days, you鈥檒l travel deep into the outback, tracing the footsteps of prehistoric giants and uncovering the secrets of Earth鈥檚 ancient history.

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A rich and complex ecosystem stretching back 700,000 years that included woolly mammoths, bison, horses and big cats has been unveiled thanks to DNA preserved in frozen faeces.

(鲍谤辞肠颈迟别濒濒耻蝉听辫补谤谤测颈颈) are rodents about 40 centimetres long, found in cold regions of both North America and Siberia. These areas were joined by a land bridge in the past, with the whole region being known as Beringia.

鈥淭he squirrels hibernate for about eight months of the year, and in the four months that they鈥檙e conscious, they really need to get out there and eat and bring as many resources as they can back to their burrow,鈥� says at the Hakai Institute in Campbell River, Canada.

This means their burrows often contain a wealth of faecal pellets and food caches, which makes the animals like 鈥渘atural archivists鈥�, says Murchie. To see what might be stored in this archive, he and his colleagues looked at preserved faeces 鈥� known as coprolites 鈥� from 13 Arctic ground squirrel burrows in the central Yukon in Canada that were frozen in permafrost.

The burrows dated to between about 700,000 and 30,000 years ago. From the droppings, each of which is about 1 to 2 centimetres long, the team extracted DNA belonging to a wide range of organisms.

These include microbes, more than 200 different plant groups and animals including insects, other rodents, woolly mammoths, horses, grey wolves, steppe bison and a big cat that was either an or a cougar. 鈥淚t鈥檚 the whole cast of organisms that lived in the Beringian ice-age ecosystem,鈥� says Murchie.

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You might assume that ground squirrels would primarily eat nuts and seeds, but that鈥檚 not the case, he says. 鈥淭hey鈥檙e actually quite omnivorous, almost like little bears. There are reports of ground squirrels eating carcasses of moose and lynx, so the fact that we find all of these large animals in their coprolites isn鈥檛 actually that surprising.鈥�

Murchie and his colleagues were able to use the DNA they found to reconstruct mitochondrial genomes of many animals from different points in time. These included 12 ground squirrels 鈥� one lineage of which dated back 700,000 years 鈥� three horses, two bison and one hare. They also found enough DNA to piece together six woolly mammoth genomes, but details of those will be published separately.

鈥淭hese are fantastically preserved samples that really showcase the ecological diversity of the Yukon through time,鈥� says at Clemson University in South Carolina.

She says it is hard to know whether DNA from a given species is present in a coprolite because it was eaten by a ground squirrel, or because it existed in the environment and leached in. But she does say it is feasible that the rodents consumed mammoth meat, given how much DNA was present in the samples and that ground squirrels are often scavengers.

The asteroid strike that wiped out the dinosaurs hit with such force that it took at least 8 million years for the impact site to cool down, creating a warm underground ecosystem where microscopic life thrived.

The Chicxulub asteroid, which collided with Earth 66 million years ago at what is now Mexico, is thought to have been as large as 15 kilometres in diameter. The strike caused so much climate chaos that it wiped out three-quarters of species on Earth. All the dinosaurs except the ancestors of birds became extinct and a nuclear winter gripped the planet for at least 15 years.

Its effects were also felt deep underground. 鈥淭he Chicxulub impact was big enough to cause deformation at least 35 kilometres under the surface of the Earth, detectable using geophysical surveys,鈥� says at the University of Glasgow, UK.

The impact melted about 10,000 cubic kilometres of rock, she says. The combination of melted rock and seawater created porous material filled with tiny pockets of hot water, known as a hydrothermal system.

Because of the presence of minerals that only form where there is liquid water and heat, we know that the asteroid would have created hydrothermal environments to depths of several kilometres. But the scale and lifespan of the heating and resulting hydrothermal system has, it seems, been massively underestimated.

Previously, it was thought it took only 2 million years for the impact site to cool down. Now, Pickersgill and her colleagues say it may have taken at least four times longer, giving hydrothermal life much more time to thrive.

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鈥淥ne of the biggest unknowns about all impact-generated hydrothermal systems, and Chicxulub in particular, is how long the heat keeps water circulating through the structure,鈥� says Pickersgill.

To figure this out, the team drilled 1 kilometre into the crater to obtain rock cores. Because potassium in the rocks has decayed into argon gas over time, the researchers could measure the amount of argon trapped in the samples to find out their age.

鈥淲e got a range of ages from the time of impact at 66 million years ago to about 58 million years ago,鈥� says Pickersgill. 鈥淭hat told us that hydrothermal activity was ongoing in at least part of the Chicxulub structure for 8 million years after the impact.鈥�

Sulphur isotopes in the cores provide evidence that microbial life existed in the hydrothermal system and recovered rapidly after the impact.

The results mean that the very earliest impact craters on the young Earth 鈥� and perhaps other worlds 鈥� may also have had habitable hydrothermal systems for longer than previously known.

鈥淭his provides more opportunity for life to develop, evolve and spread,鈥� says Pickersgill. 鈥淚t supports the concept that early life on Earth may have found a long-term home in impact craters, and possibly even life on other planets where these massive impact craters are dominant surface features.鈥�

at Curtin University in Perth, Australia, says while there is 鈥渘ot an entirely unambiguous record of continuous hydrothermal activity鈥� at Chicxulub, the evidence is strong that the impact site stayed hot for millions of years.

鈥淟arge impacts do not simply destroy environments,鈥� he says. 鈥淭hey can also create long-lived underground systems where hot fluids circulate through shattered rock. These chemically rich settings may provide sheltered habitats for microbes and perhaps even favourable conditions for some of the early chemical steps towards life.鈥�

With jaws like these, who needs big arms? A new analysis suggests dinosaurs like Tyrannosaurus rex had shrunken forelimbs because their massive, powerful heads became their primary tool for killing large prey, rendering their arms redundant. It is an evolutionary approach that five different lineages of large theropod dinosaurs took independently.

Researchers are well aware that a number of large, predatory theropods followed a trend towards bigger bodies, bigger heads and smaller, shorter arms over time. But it wasn鈥檛 known why this pattern repeated across multiple predatory dinosaur families, scattered across the globe and separated by many millions of years, says at University College London. There was also little understanding of how the bones in their ever-heftier skulls changed as their arms became proportionally smaller.

鈥淭his paper tackles one of the big evolutionary questions in theropod dinosaurs,鈥� says at the University of Bristol, UK, who wasn鈥檛 involved with the research.

Scherer and his colleagues compiled data on the proportions of the forelimbs and skulls of 85 theropod species, along with body-mass data. This allowed them to calculate a ratio between the skull dimensions and forelimb lengths, quantifying just how small the arms were compared with the head. The researchers then compared this ratio with other measurements of the dinosaurs鈥� bodies, along with a measure of the skulls鈥� strength based on factors such as bite force and skull rigidity.

The team found that skull durability was associated with smaller arms, regardless of where the species sat in the theropod evolutionary tree. 鈥淚f it鈥檚 a predatory theropod and has a very robust skull, it will most likely have relatively small forelimbs,鈥� says Scherer.

The researchers found this head-arm divergence evolved independently in five theropod groups: tyrannosaurids, the short-snouted abelisaurids, the knife-toothed carcharodontosaurids, ceratosaurids and megalosaurids. This evolutionary pattern hadn鈥檛 been identified in the last two groups until this study, points out at the Beipiao Pterosaur Museum of China, who wasn鈥檛 involved in the research. This shows how hidden evolutionary signals can be revealed when traits are quantified in this way, she says.

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The findings provide clues as to why the dinosaurs鈥� arms kept shrinking. These predators鈥� increasing skull strength and body size coincided with the rising mass of their quarries. The theropods evolved huge, sturdy skulls for subduing their large, difficult-to-control prey. Their heads were clearly doing the majority of the work, says Scherer, reducing the need for strong, grappling arms.

鈥淣ature doesn鈥檛 like to have everything all at once,鈥� he says. A big, powerful head plus strong forelimbs would require a lot of energy to maintain.

This creates a trade-off between jaws and claws. Other theropods like the megaraptorans and spinosaurs were also very large predators, but they took the opposite route to dinosaurs like T. rex, coupling聽long arms with slender skulls.

Rowe is curious about the mechanical function of the jaw-centric theropods鈥� arms, even in their shortened state. 鈥淵es, tyrannosaurs had tiny, vestigial arms, but that does not necessarily mean they were completely useless,鈥� he says.

He adds that the study emphasises the evolutionary diversity of dinosaurs. 鈥淚t reminds me of why I fell in love with dinosaurs in the first place,鈥� he says. 鈥淭hey were some of the most innovative and successful animals to ever exist.鈥�

Fossil hunting in the Australian outback

Join this extraordinary adventure through the heart of Australia鈥檚 fossil frontier. Once a shallow inland sea millions of years ago, eastern Australia is now a hotspot for fossils. Over 13 unforgettable days, you鈥檒l travel deep into the outback, tracing the footsteps of prehistoric giants and uncovering the secrets of Earth鈥檚 ancient history.

Read more

Australia was once home to a second species of koala that lived only in the west of the continent, where it became extinct around 30,000 years ago.

Today, there is only one koala species: Phascolarctos cinereus. It is found almost exclusively in eucalyptus forests in eastern Australia and is threatened by habitat loss, disease, collisions with cars and predation by introduced species.

Numerous koala fossils, aged between 137,000 and 31,000 years old, have been collected in Western Australian caves over the past century. Until now, however, there wasn鈥檛 enough material to conclude that the remains were from a different species.

In the past 25 years, more fossils have become available to researchers, including skulls donated by the family of late speleologist Lindsay Hatcher, who discovered numerous ancient remains during his expeditions in caves in the south-west of Western Australia.

鈥淎mongst the donation was a koala skull in very good condition,鈥� says at the Western Australian Museum. 鈥淯pon examination of that skull, we noticed differences with modern koalas that got us to start working on the fossil material in the collection.鈥�

To the untrained eye, the new species, named Phascolarctos sulcomaxilliaris, would have been difficult to distinguish from P. cinereus, but there are subtle differences.

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鈥淚n short, the Western Australian koalas were same-same but different,鈥� says Travouillon. 鈥淭hey had shorter heads, for sure, and they seem to have less-well-developed chewing muscles than the east-coast koalas. But they simply chewed in a different way by having larger teeth and having a more efficient, shorter jaw to break down the leaves.鈥�

A large groove on the cheek of P. sulcomaxilliaris suggests the animal had a larger muscle attached there that was used to either move a larger lip, with which it perhaps grabbed leaves, or inflate its nostrils to be able to smell leaves over a greater distance. Its skeleton was also less agile, suggesting it spent less time moving between trees.

When the climate dried and Western Australia鈥檚 forests disappeared about 30,000 years ago, P. sulcomaxilliaris vanished, along with many other animals that once shared its habitat. 鈥淭here would have been [Tasmanian] devils, thylacines, giant echidnas, short-faced kangaroos and the giant marsupial Zygomaturus,鈥� says Travouillon.

鈥淥ur first peoples in Western Australia would have lived amongst them and they would have been witness to their extinction.鈥�

at the Australian Museum in Sydney says the study makes a 鈥渃onvincing case for the distinctiveness of the Western Australia koalas as a unique species鈥�. 鈥淚 look forward to seeing if any DNA can be extracted from the fossils,鈥� he says.

Fossil hunting in the Australian outback

Join this extraordinary adventure through the heart of Australia鈥檚 fossil frontier. Once a shallow inland sea millions of years ago, eastern Australia is now a hotspot for fossils. Over 13 unforgettable days, you鈥檒l travel deep into the outback, tracing the footsteps of prehistoric giants and uncovering the secrets of Earth鈥檚 ancient history.

Read more

Birds today have dinosaur DNA. They have dinosaur blood in their veins. Birds evolved directly from Velociraptor-type animals and are the only true dinosaurs that still exist. Steve Brusatte is a palaeontologist at the University of Edinburgh, UK, and has been studying 150 million years’ worth of bird evolution, from surviving the asteroid that wiped out their contemporaries to today鈥檚 adaptation into almost every niche. Brusatte introduces elephant birds, terror birds, demon ducks and penguins the size of gorillas, and why “when gulls dive bomb you and try to steal your pasty or your chips鈥�, says Brusatte, “you really can sense in the nastiness, the cunning, the agility, the feistiness. You can sense that inner Velociraptor.鈥�

Read more: The evolving science of dinosaurs