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. “If 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.”

The Late Triassic seas contained a multitude of marine reptiles, but lurking on the sea floor was something different: a marine amphibian. A fossil of the large, bottom-dwelling ambush predator discovered in China is the first evidence that amphibians once found a way to adapt to life in the ocean.

Named Gerrothorax maritimus, the near-perfect and exquisitely preserved 74-centimetre-long fossil was found by farmers in what is now a national geopark in Guanling county, China.

The researchers who studied the fossil think that its secret to survival in salt water, which is normally fatal to amphibians because of their permeable skin, probably lay in its strong body armour.

“It was a flat animal that lived on the sea floor,” says at the University of California, Davis, who was part of the team that analysed the fossil. It was probably an ambush feeder, he says, as its wide mouth and the strong hyoid bone in its neck suggest it used suction feeding, as is seen in some modern bottom-dwelling predators of a similar size that use an ambush strategy, such as wobbegong sharks.

As soon as the researchers began to study the fossil, they knew it was neither fish nor reptile. It had to be an early amphibian because of its tell-tale anatomy, which included its four legs and gills.

There is, however, no evidence that the creature underwent metamorphosis, as many modern amphibians do, such as when tadpoles become frogs, says Motani.

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To prove that the animal was indeed marine and not just a land-based creature washed into the sea after death, the researchers studied the strontium isotope ratios of the fossil bones.

They found that the remains of the new species had a clear signature of sea water, meaning G. maritimus grew to adulthood while in the ocean. Palaeogeographic reconstructions also suggest that, 237 million years ago in the Late Triassic Period, the location in which the fossil was discovered was at least 30 kilometres away from land.

The fossil was also recovered alongside that of a large marine reptile: an ichthyosaur called Guizhouichthyosaurus, which reached lengths of 7 metres.

Interestingly, the closest relative to G. maritimus lived in freshwater environments. A fossil of this amphibian, Gerrothorax pulcherrimus, was first described nearly a century ago.

This has led the researchers to suggest the marine lifestyle of G. maritimus was an accident of evolution. “There was a freshwater amphibian that happened to have the equipment needed to colonise the sea – the body armour,” says Motani.

The armour originally protected the Gerrothorax genus from predators in fresh water. But because it formed an impermeable barrier, it could also help the amphibians survive in seawater, he says.

Although it is commonly believed that “amphibious” means the ability to be on land or in the water, this is a misconception, says Motani. There are many modern newts that never leave the water, yet they are amphibians, he says.

Spectacular fossil preserves internal organs of ancient marine reptile

A stunningly intact marine reptile named Austronaga minuta that lived around 245 million years ago may have looked like a miniature version of more famous later ocean predators, like plesiosaurs

“My take is that it is similar to calling a snake a tetrapod, when it does not have limbs,” says Motani.

at Flinders University, Australia, says the fossil is a first, given that none of the 8000 or so living species of amphibians today is fully adapted for life in the sea.

“If not for the marine invasion by many groups of reptiles at the same time, they might have even had a chance at diversifying in this niche, but that clearly didn’t occur,” he says. “It shows us that amphibians closely related to modern forms were able to adapt to different environments, like seawater, in ways we never thought possible.”

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.

The story of how Homo sapiens left Africa is more complicated than we once thought.

Fossils suggest our species reached parts of Eurasia far earlier than the major migration traditionally dated to around 60,000 years ago. So who were these early pioneers and why did their populations disappear?

In this video, we explore the latest fossil, archaeological and genetic evidence reshaping the Out of Africa model. From a 210,000-year-old Homo sapiens skull found in Greece to evidence that our species may have evolved through interconnected populations across Africa, a new picture of human origins is emerging.

We also investigate a fascinating possibility: that stronger social networks, and the exchange of ideas and new technologies, helped Homo sapiens become adaptable enough to thrive in environments across the planet.

The story of humanity may not be of one great migration, but a long history of exploration, failure, connection and, eventually, survival.

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.”

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.”