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鈥檝e 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.

The world鈥檚 deepest known whale graveyard has been discovered in the southern Indian Ocean at a depth of 7 kilometres. The remains found there include a new species of extinct beaked whale and other fossils that are over 5 million years old.

In early 2023, at the Chinese Academy of Sciences and his colleagues undertook 32 dives in a crewed submersible along 1200 kilometres of the seafloor, in an area known as the Diamantina Zone.

The expedition was part of the Global Hadal Exploration Programme, an effort led by Chinese scientists to explore all the deepest parts of the planet鈥檚 oceans, which range from 6000 to 11,000 metres below the surface. At these depths there is no light, and life must survive on what falls from the surface or generate its own energy from chemicals 鈥� known as chemosynthesis.

The first whale fossils were found at a depth of 7002 metres in a part of the Diamantina Zone known as the Dordrecht Deep, which is over 1100 kilometres south-west of Perth, Western Australia.

鈥淲ith the sub鈥檚 powerful lighting system, we could see tens of metres around us on the otherwise pitch-dark seafloor,鈥� says Zhou. What they saw was 鈥渁 little scary, but also incredibly fascinating鈥�, he says.

The researchers estimated there were up to 760 individual whales per square kilometre, including both ancient and recent carcasses, constituting what they have called a 鈥渨hale necropolis鈥� and a 鈥渄eep-sea fossil megasite鈥�.

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The recently fallen carcasses, which included a 5-metre-long Antarctic minke whale (Balaenoptera bonaerensis), provide food to a thriving ecosystem of invertebrates 鈥� such as bone-eating worms and brittle stars 鈥� many thought to be new species, found in densities of up to 2800 individuals per square metre.

鈥淚t felt profoundly special,鈥� says Zhou. 鈥淲e were looking at the final resting place of millions of whales 鈥� some over 5 million years old 鈥� a deep-time archive of evolution and deep-sea life. It was humbling and awe-inspiring, and we treated the site with the respect it deserves.鈥�

Altogether, the team found 485 active whale-fall and fossil-whale sites during their expedition. Using the submersible鈥檚 robotic arms, they collected 43 fossil specimens that were dated to between 120,000 and 5.26 million years old.

Among the younger fossils, most were beaked whales belonging to two living species, Andrews鈥� beaked whale (Mesoplodon bowdoini) and the strap-toothed whale (Mesoplodon layardii).

So far, the team has formally described one new species, named Pterocetus diamantinae. However, they also collected several fragmentary specimens that may include further species that are unknown to science, says team member at the University of Pisa, Italy.

at the Chinese Academy of Sciences, another team member, says there are a number of factors that mean the whales have been so well preserved. Most of these fossils are beaked whales鈥� rostra, or snouts. 鈥淭hey鈥檙e hyper dense, almost like bone armour, which makes them physically resistant to degradation and less palatable to bone borers,鈥� says Peng.

Only about 0.05 to 0.55 鈥痬illimetres of sediment has been deposited per thousand years, over the past 5 million years in this region, and many of these bones are coated with ferromanganese oxides, which effectively seals them off from the surrounding environment.

鈥淪o it鈥檚 really a combination of bone density, slow burial, and mineral coatings that has allowed these bones to escape being eaten for over 5 million years,鈥� says Peng.

The team thinks that a number of factors have led to such a concentration of whale deaths in the Diamantina Zone, including a whale-migration route passing through the area and a V-shaped topography that funnels the carcasses to the trench floor.

at Macquarie University in Sydney, Australia, who was not part of the study, described the find as an 鈥渁mazing discovery鈥�. 鈥淭he density of the whale-fall remains is incredible,鈥� he says.

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.

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