A nondescript 115-million-year-old fragment of leg bone has yielded spectacularly preserved red blood cells, which may be the earliest ever found in dinosaurs.

Red blood cells have previously been found in dinosaur remains, including 75-million-year-old bone fragments collected in Canada in 2015 and the femur of a Tyrannosaurus rex that died 68 million years ago, found in Montana in 2005.

Now, at Curtin University in Perth, Australia, and her colleagues say they have isolated the oldest-ever dinosaur red blood cells from the hind-limb of a theropod dinosaur, Aratasaurus museunacionali, found in Brazil in 2008.

The Aratasaurus individual studied by the team wasn’t yet fully grown, with an estimated body length of just over 3 metres, and weighed about 34 kilograms.

“The fossils we worked on are not display specimens by any means, so they don’t look very interesting,” says Grice. ���� you look at them, you think there’s just a bunch of bones and there’s probably not much in there.”

Grice cut thin sections of bone, mounted them onto glass slides and used hydrochloric acid to remove surrounding rock – and she was shocked at what she saw.

“I was jumping up and down,” says Grice. “I ran up to my head of school’s office and was so excited that he gave me a whisky to calm me down. No one has ever seen dinosaur red blood cells in high resolution before.”

The cells she found were abundant: in a single slide, just a fifth of a millimetre wide, there were 20 blood cells. All of the cells were within fossilised blood vessels, providing further evidence that they really were red blood cells.

Liquid chromatography–mass spectrometry analysis revealed the presence of haem B, a constituent of haemoglobin that binds to oxygen, adding molecular evidence of the type of cell.

The team also had to rule out the possibility of any contamination, especially from the sediments in which the fossil was preserved, which were dominated by algae.

The cells found outside the bone were dominated by chlorophyll-derived compounds, whereas those inside contained haem-derived molecules, which strongly suggests that the latter cells weren’t a result of contamination.

The researchers also compared the blood cells to those of the closest living relatives of the dinosaur fossil, birds and crocodiles. The Aratasaurus red blood cells are significantly larger. This could indicate that the cells swelled during fossilisation, or that the species grew much bigger than the fossilised specimen.

at the Natural History Museum in London says previous studies reporting red blood cells in fossils tens of millions of years old are contentious, with some researchers suggesting they could be the result of bacteria or artefacts of the fossilisation process. “This paper is further evidence that fossilised soft tissues such as red blood cells can preserve over geological timescales,” she says.

Grice says the discovery may mean that other nondescript dinosaur fossils that have been locked away in museum collections may hold profound secrets. “There’s drawers and drawers of fossil material, which don’t look very nice,” she says. “This kind of work opens up a whole new opportunity to unlock those collections and bring modern technology and molecular techniques to these specimens.”

Meet Invictibellatrix amberina, the unconquered female warrior – a new species of predatory dinosaur related to Tyrannosaurus rex that hails from the Isle of Wight in southern England.

The fossil used to identify it – a partial braincase – has been lying in the archives of the Natural History Museum in London since it was acquired from a Reverend Reginald Hooley in 1924. “It was sitting unstudied in the museum for about 100 years, which is very surreal,” says , now at the University of Leeds, UK.

Morrison and his colleagues used CT scans to create a 3D scan of the fossil and compared it with features of other dinosaurs.

The closest match was the Argentinian megaraptoran from about 80 million years ago. So, the researchers suggest that the skull, originally found in 120-million-year-old rocks from the Lower Cretaceous Wessex Formation on the south-west coast of the Isle of Wight, is from a new species belonging to the Megaraptora group of carnivorous dinosaurs. If so, it is the first time a megaraptoran has been discovered in Europe.

A similar-looking dinosaur is known from a few million years earlier in the Wessex Formation: the 5-metre-long . However, the parts we have hint that it belonged to the sister group of tyrannosaurs and none of the fossilised remains of the two individuals directly overlap, so it is hard to compare them.

The genus name Morrison and his colleagues have given to the newly described fossil, Invictibellatrix, means female unconquered warrior. They estimate that it was an agile, two-legged carnivore that was about 3 to 4 metres long, some 1.5 metres tall and weighing between 200 and 300 kilograms. It is likely to have had feathers and claws 10 to 20 centimetres long for attacking small dinosaurs, lizards and mammals, says Morrison.

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Had we been around then, “humans would have been perfect-sized prey, about a third of their body weight,” he says.

At the time, the Isle of Wight was still firmly attached to both mainland Britain and the rest of Europe, and the environment would have been subtropical, says Morrison.

Megaraptoran fossils have been found in Asia, Australia and South America, and finding one in Europe would begin to tie their story together.

Morrison suggests that Invictibellatrix evolved from Asian megaraptorans that dispersed into Europe some 130 million years ago. Then megaraptorans spread from Europe to Africa, then to South America and Australia before the continents completely separated.

at Monash University in Melbourne says it is a shame more detailed comparisons couldn’t be made with Eotyrannus, which has previously been considered a relative of megaraptorans.

���� Invictibellatrix is indeed a megaraptoran, it expands the palaeobiogeographic range of the group and plugs a significant gap in our knowledge, linking those from South-East Asia to Australia and South America via Europe and Africa,” he says. “However, more fossils are required to support or reject this hypothesis.”

A semi-aquatic forebear of living mammals that lived alongside the dinosaurs was also the first known animal capable of suckling.

“The mammalian ways of swallowing and suckling are unique,” says at the University of Chicago. “It is one of several biological adaptations of mammals that stand out from all other vertebrates.”

Luo and his colleagues have discovered a new genus of mammaliform, a creature that lived before the last common ancestor of the living mammalian groups – monotremes, marsupials and placentals – that would have been able to chew and suck.

It is also the earliest known example of a mammal that evolved for a semi-aquatic lifestyle. The animal has been dubbed Megacauda sungei, referencing its broad tail and palaeontologist Sun Ge.

The fossil, which is dated to between 163 million and 168 million years ago, was found by local farmers in the Daohugou area of Inner Mongolia, China.

“It is a chimera,” says Luo. “The back half of Megacauda is more similar to the platypus, of all mammals. But the skull and teeth are analogous to river otters.”

With an estimated weight of 1 kilogram, the creature is the largest known mammaliform from the Middle-Late Jurassic, when the planet was dominated by dinosaurs.

The pelvis is preserved in 3D, as are its hyoids, or throat bones. The bone structures under the skull that form the roof of the mouth and throat passage are also visible.

This meant that, for the first time in any mammaliform, scientists were able to reconstruct the animal’s entire throat anatomy.

Mammals’ throats can form “a suction vacuum for milk and squeeze the chewed food balls and liquid down their throats”, says Luo. All the features that enable this are present in Megacauda.

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“We used to know very little about the evolutionary pattern of pharyngeal and hyoid structure. Now we know their evolutionary origins went back to before the rise of the modern mammals,” he says.

The researchers found tiny limb fragments in the fossil’s stomach area that resembled the bones of salamanders, which would have lived in the same environment and may have been the creature’s last meal.

at Macquarie University in Sydney says this fossil sits at a key point in mammalian evolution. “It tells us that some key mammalian traits like sucking, which is required for behaviours like drinking milk from mothers, predate the origin of mammals today.

“It also is cool to see that this sister lineage to today’s mammals had evolved an aquatic lifestyle, which is something we have seen multiple times across the mammalian family tree, including in the platypus,” says Griffith.

A newly identified species of bovine, currently known only as yak X, was probably hunted by ancient humans including Neanderthals, Denisovans and our own species, say the researchers who discovered it.

“It’s not every day that one discovers a previously unknown extinct megafaunal species,” says at Stockholm University, Sweden.

He and his colleagues began studying bone fragments recovered from Denisova cave, in the foothills of the Altai mountains in Siberia, Russia, in the hope of learning about bison evolution. The cave is most famous as the place where the mysterious Denisovans were first identified from a finger bone found there.

“But it turned out that nearly all bone fragments in the cave had DNA that didn’t match any living bovine species, nor did it match the extinct steppe bison or aurochs,” says Dalén.

The team was given access to hundreds of tiny bone fragments from the cave and also analysed material from three other nearby sites and one near the Ural mountains, says , also at Stockholm University. From these, the researchers were able to construct genomes from 20 individuals.

The species seems to have diverged from the wild yak (Bos mutus) around 400,000 years ago. By 250,000 years it appears to have become genetically isolated and then extinct by around 30,000 years ago.

The divergence time is similar to that between polar bears (Ursus maritimus) and brown bears (Ursus arctos), says Dalén.

This means yak X was probably quite a different animal, just as American and European bison are no longer the same species.

But until further work is complete, including on other remains that may have been previously misidentified, the team has no idea what unique traits the new species may have had.

“We suspect that yak X might actually correspond to yak-like remains that have been [previously] described by Russian palaeontologists as a subspecies of the Himalayan yak,” says Dalén.

All of the bones found so far are much lower in elevation than areas in the Tibetan Plateau that are the native range of modern yaks. This means that yak X may have been less adapted to extreme mountain environments, says , also at Stockholm University.

There is, so far, no direct evidence of yak X being hunted by different human species, but it is likely that Denisovans, as well as Neanderthals, modern humans and large carnivores, such as hyenas and lions, targeted them as prey, says Dalén. “Our results show that yak X was present in the region for more than 200,000 years, and they will likely have had first-hand experience of Denisovans, Neanderthals and modern humans coming and going.”

The world’s most famous dinosaur, Tyrannosaurus rex, was probably warm-blooded like birds and mammals, new evidence, obtained from 66-million-year-old tooth enamel, suggests, adding weight to previous findings.

at South Carolina State Museum, who wasn’t involved in the new study, says the research means “the opening to the last Jurassic World flick was one big pile of Hollywood bunk”.

“That film premised that dinosaurs could not survive in the modern world, except near the equator,” says Persons. “Not so. The evidence indicates that a Tyrannosaurus would be comfortable in subtropical and even mild climates.”

at the University of California, Los Angeles, and his colleagues analysed the chemistry in the enamel of three T. rex teeth and compared them with five similarly aged fossilised crocodile teeth.

The researchers also compared their results with data from mammals such as elephants and mammoths to try to determine whether T. rex was also an endotherm – an animal that can regulate its body heat through its metabolism. Ectothermic, or so-called cold-blooded animals like crocodiles, often warm up by basking in the sun instead.

Endothermy is common in large animals and even some fish, says Eagle, allowing them to move around and exhibit more sustained activity to find food and migrate, and to live in colder environments. It has long been thought that many dinosaurs, including T. rex, were also warm-blooded.

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“It comes at a cost though – higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it,” he says.

Within the enamel chemistry, the researchers focused on the abundance of bonds between rare heavy isotopes of carbon and oxygen, known as carbon-13-oxygen-18 bonds. These bonds are more abundant in minerals that form at cold temperatures than minerals that form at warm temperatures.

“Therefore, in a very old tooth we can measure carbon-13-oxygen-18 bond abundance and figure out whether it formed in a hot or cold body.”

He says T. rex had a body temperature of around 36°C, similar to large modern mammals but below many modern birds.

“We also found that the reconstructed temperature of T. rex was significantly elevated compared to temperatures derived from crocodile teeth from the same geological formation – Hell Creek in Montana,” Eagle says.

The researchers also say that T. rex body temperatures were higher than the ambient temperatures in prehistoric Montana, reconstructed both from isotopic estimates and climate models.

“Using thermal performance curves and climate modelling based on these results, we found that the entire North American continent would have been habitable for T. rex in the Cretaceous Period,” he says.

The shocking fossils that show T. rex wasn’t the king of the dinosaurs

We've always thought that Tyrannosaurus rex was an unchallenged apex predator during the dying days of the dinosaurs. But a fresh look at controversial fossils has prompted palaeontology’s biggest-ever U-turn

Persons says there was already extensive evidence that T. rex was warm-blooded, including bone growth rates and predator-prey ratios – with energy-hungry endotherms than ectotherms – and a “slew of anatomical traits consistent with high-performance athleticism”.

at Carthage College in Wisconsin says the new work is an “example of science in action, converging upon a single, robust hypothesis, which in this case reveals T. rex as an active top predator”.

The researchers “make the case for a wide geographic distribution for T. rex, showing that it could tolerate cool temperatures in the north of its range and tolerate the tropical temperatures in the south”, says Carr. “And in both cases, T. rex‘s body temperature is higher than the average air temperature. That result is consistent with the hypothesis that T. rex might have migrated from Asia into North America at high latitudes.”

Our modern environment is nothing like the one we evolved for. In our latest video, we speak with Daniel Lieberman, palaeoanthropologist and author of Fed Up, to explore how this mismatch has led to some of the greatest health challenges of our time.

From ultra-processed foods to body fat, Lieberman explains why nothing in diet and health makes sense except in light of evolution.

What is the optimal diet and physical activity level according to evolution? And how can false evolutionary reasoning lead to untenable dieting? Join us as we feast on millions of years of human evolution, and how it never prepared us for modern life.

Creatures that bridged the gap between reptiles and mammals may have been bearing live young 90 million years earlier than we thought.

One of the hallmarks of all mammals apart from monotremes – echidnas and the platypus – is that they give birth to live young. This “viviparity” contrasts with the “oviparity” seen most other vertebrates, in which females lay eggs that hatch outside their bodies.

One long-standing question has been whether creatures known as cynodonts, which emerged around 260 million years ago during the Permian geological period and are directly ancestral to all mammals, laid eggs or gave birth to live young, as no evidence of their reproduction has been discovered either way.

“Whether mammalian ancestors were oviparous or viviparous has been considered a mystery,” says  at Argentina’s National Scientific and Technical Research Council. “We had no clues on how or when one of the most distinctive traits of the majority of present-day mammals, viviparity, evolved in the mammalian lineage.”

This has now changed, thanks to a chance observation made during a postgraduate class at the University of Buenos Aires in Argentina. The students were examining a fossil of Chiniquodon theotonicus, a cynodont that lived 236 million years ago and was unearthed in the Talampaya National Park in north-western Argentina in 2011. Part of the analysis involved using a microscope to examine thin slices taken from one of the ancient animal’s leg bones. At that point, the class noticed a curious growth line inside the bone.

Gaetano and his colleagues investigated further and eventually concluded that this line, analogous to a tree’s growth ring, recorded the moment that the ancient mammal relative went through a growth spurt after its birth. 

The researchers reconstructed how large the leg bone and the animal itself would have been when the growth line formed. They calculated that the animal would have weighed 1.68 kilograms at that point. When the animal died as a full-grown adult, it was just shy of 12 kilograms.

This gave the researchers a ratio of newborn to adult size in the ancient animal. They then compared this figure to similar ratios obtained from a wide variety of modern animals: 1869 mammals, 2619 non-avian reptiles and 782 birds.

“We were amazed to find that ��󾱲Ծ���ܴǻ�Dz���grouped with extant placental mammals,” says Gaetano.

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Egg-laying animal groups produce young that are far smaller than adults when they hatch, he says.

For example, some species of large birds have newly hatched young that are just 0.002 per cent of adult body mass, whereas placental mammals often give birth to young that are over 20 per cent of the size of their parents.

“Only placental mammals produce relatively large newborns, whereas reptile and bird hatchlings are comparatively very small,” says Gaetano. “Hence, we propose that [the] Chiniquodon theotonicus reproductive strategy was most similar to that of placental mammals.”

 at the University of Bristol in the UK says the findings are convincing.

“Further, as they argue, the apparent absence or rarity of actual eggs of any kind in the Permian and Triassic has always been puzzling – the so-called amniote egg gap,” he says.

 at Macquarie University in Sydney says his gut reaction is to be sceptical of the claim of live birth, as we have only indirect evidence. But he is impressed that, in the absence of any direct fossil evidence, the team is still trying to solve the puzzle.

“We may never get any of the kind of direct evidence that solves the
mystery, for example a fossilised mammalian egg or a fossil mother during
pregnancy,” he says. “So it is kind of cool that they’re taking a different approach to trying to find an answer to that question.”

A tiny, long-necked marine predator that lived 245 million years ago is the oldest reptile ever found with an intact digestive system.

The exquisitely preserved fossil, including almost the entire skeleton as well as the stomach, liver and intestines, was found in Yunnan province in China in 2023 and is named Austronaga minuta.

Even blood vessels and the scales of a partially digested fish meal are visible in the remains.

“A fossil this age with such clear preservation of its organs is really a world treasure,” says at Flinders University in Adelaide, Australia, who wasn’t involved in the research.

Austronaga dates back to the Triassic Period, when dinosaurs first evolved, but it isn’t a dinosaur. It belongs to a broader group called archosaurs, which includes dinosaurs, birds and crocodiles, but not other famous marine reptiles like mosasaurs or ichthyosaurs.

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The archosaurs were incredibly diverse in the Triassic and included “all kinds of interesting and strange-looking reptiles”, says at the Natural History Museum Stuttgart, Germany, a member of the team that analysed the fossil. Only later, during the Jurassic and beyond, did they become more restricted, mostly being limited to dinosaurs, including birds, and crocodiles.

This specimen is a mere 60 centimetres in length, but as it is the only known example and the reptile’s age at death is unknown, it is impossible to say whether the species grew larger, says Spiekman.

However, he is confident that it was unlikely to have reached the size of its very long relative Dinocephalosaurus, the “Chinese sea dragon”, which could easily grow to over 4 metres.

“This was certainly a good and agile swimmer, mainly using its tail for swimming, its long front flippers for steering and its long neck to catch fish,” says Spiekman. “A�ܲ��ٰ��DzԲ����� probably would have looked a little like a lizard or a croc trying to be a seal or an otter and likely would have had scaly skin, for example.”

The fossil shows that the basic plan of the reptilian digestive tract has changed little in 245 million years, he says, and the “straight and simple intestines is what we see in most modern predatory reptiles, including those eating fish”.

Although the fossil is of high quality, the internal organs of Austronaga are only preserved in two dimensions. This is unlike those of a 380-million-year-old fossil of an armoured fish that Long and his colleagues , which is regarded as having the oldest known organs of any vertebrate.

“But this is still an incredibly well-preserved fossil,” he says.