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

鈥淭he mammalian ways of swallowing and suckling are unique,鈥� says at the University of Chicago. 鈥淚t is one of several biological adaptations of mammals that stand out from all other vertebrates.鈥�

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 鈥� monotremes, marsupials and placentals 鈥� 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.

鈥淚t is a chimera,鈥� says Luo. 鈥淭he back half of Megacauda is more similar to the platypus, of all mammals. But the skull and teeth are analogous to river otters.鈥�

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鈥檚 entire throat anatomy.

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

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鈥淲e 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,鈥� he says.

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

at Macquarie University in Sydney says this fossil sits at a key point in mammalian evolution. 鈥淚t 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.

鈥淚t also is cool to see that this sister lineage to today鈥檚 mammals had evolved an aquatic lifestyle, which is something we have seen multiple times across the mammalian family tree, including in the platypus,鈥� 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鈥檚 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鈥檛 involved in the new study, says the research means 鈥渢he opening to the last Jurassic World flick was one big pile of Hollywood bunk鈥�.

鈥淭hat film premised that dinosaurs could not survive in the modern world, except near the equator,鈥� says Persons. 鈥淣ot so. The evidence indicates that a Tyrannosaurus would be comfortable in subtropical and even mild climates.鈥�

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 鈥� 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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鈥淚t comes at a cost though 鈥� higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it,鈥� 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.

鈥淭herefore, 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.鈥�

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

鈥淲e also found that the reconstructed temperature of T. rex was significantly elevated compared to temperatures derived from crocodile teeth from the same geological formation 鈥� Hell Creek in Montana,鈥� 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.

鈥淯sing 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,鈥� he says.

The shocking fossils that show T. rex wasn鈥檛 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鈥檚 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 鈥� with energy-hungry endotherms than ectotherms 鈥� and a 鈥渟lew of anatomical traits consistent with high-performance athleticism鈥�.

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

The researchers 鈥渕ake 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鈥�, says Carr. 鈥淎nd in both cases, T. rex鈥榮 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.鈥�

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 鈥� echidnas and the platypus 鈥� is that they give birth to live young. This 鈥渧iviparity鈥� contrasts with the 鈥渙viparity鈥� 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聽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.

鈥淲hether mammalian ancestors were oviparous or viviparous has been considered a mystery,鈥� says聽 at Argentina鈥檚 National Scientific and Technical Research Council. 鈥淲e 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.鈥�

This has now changed, thanks to a chance observation made during a postgraduate聽class聽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鈥檚 leg bones. At that point, the class noticed a curious growth line聽inside聽the bone.

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

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.

鈥淲e were amazed to find that聽颁丑颈苍颈辩耻辞诲辞苍听grouped with extant placental mammals,鈥� 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.

鈥淥nly placental mammals produce relatively large newborns, whereas reptile and bird hatchlings are comparatively very small,鈥� says Gaetano. 鈥淗ence, we propose that [the]聽Chiniquodon theotonicus聽reproductive strategy was most similar to that of placental mammals.鈥�

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

鈥淔urther, as they argue, the apparent absence or rarity of actual eggs of any kind in the Permian and Triassic has always been puzzling 鈥� the so-called amniote egg gap,鈥� he says.

聽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.

鈥淲e 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,鈥� he says. 鈥淪o it is kind of cool that they鈥檙e taking a different approach to trying to find an answer to that question.鈥�

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.

鈥淎 fossil this age with such clear preservation of its organs is really a world treasure,鈥� says at Flinders University in Adelaide, Australia, who wasn鈥檛 involved in the research.

Austronaga dates back to the Triassic Period, when dinosaurs first evolved, but it isn鈥檛 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 鈥渁ll kinds of interesting and strange-looking reptiles鈥�, 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鈥檚 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 鈥淐hinese sea dragon鈥�, which could easily grow to over 4 metres.

鈥淭his 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,鈥� says Spiekman. 鈥淎耻蝉迟谤辞苍补驳补 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.鈥�

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

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.

鈥淏ut this is still an incredibly well-preserved fossil,鈥� he says.

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.