The partial skull of a dinosaur found 40 years ago has now been identified as a new species of Tyrannosaurus, and perhaps the closest relative of Tyrannosaurus rex. The research adds a new twist to a long-running debate about how many species of tyrannosaurs there were, and could help to clarify how the iconic predator evolved.

T. rex appeared in North America around 68 million years ago, 2 million years before the mass extinction that wiped out most dinosaurs. Palaeontologists have been stumped as to the carnivore’s origins. Some have suggested that the ancestors of T. rex walked over a land bridge from prehistoric Asia, while others placed its origins in southern North America.

at the New Mexico Museum of Natural History and Science and his colleagues re-examined a fossil in the museum’s collection, which was found in rock layers known as the McRae Group in western New Mexico.

While the skull had originally been categorised as T. rex, Fiorillo and his colleagues noticed differences with the bones. They propose that the specimen represents an older species, which they named Tyrannosaurus mcraeensis in reference to the rocks in which it was found.

They estimate that the dinosaur was about 12 metres long, comparable in size to T. rex, but it lived about 4 million years earlier.

The differences between T. rex and T. mcraeensis would have been relatively subtle. Whereas T. rex had prominent ridges on its brows and broad, bone-crushing jaws, the same ridges on T. mcraeensis were less well developed and its skull is more slender, says Fiorillo.

Other recent studies have proposed that there were several species of Tyrannosaurus and that some so-called T. rex fossils should be reassigned. Such proposals have been controversial, however, and largely dismissed by dinosaur palaeontologists. The new study will fuel further debate over how many Tyrannosaurus species there were in North America.

“I hesitate to regard Tyrannosaurus mcraeensis as being distinct from Tyrannosaurus rex,” says at the University of Calgary in Canada. He notes that many of the anatomical features that supposedly make the new species unique can also be found in specimens of T. rex.

Regardless of the species assignment, the existence of such a large tyrannosaur several million years before T. rex hints that south-western North America was an important centre for the dinosaur’s evolution. “The proposed age dates for the specimen are peculiar and very much warrant more study,” says Voris, as they might outline a clearer picture of dinosaur evolution in the last few million years of the Cretaceous Period.

The New Mexico tyrannosaur was found in the same rocks as giant horned dinosaurs, duckbilled dinosaurs and long-necked herbivores that could reach 30 metres in length. Fiorillo and his colleagues suggest the lineage leading to T. rex might have evolved their giant size to prey on these large herbivores, later spreading northward as the last of the “tyrant lizards” to stalk the planet.

Battered feathers and prehistoric beetle larvae encased in amber have revealed a relationship between dinosaurs and insects that stretches back more than 105 million years – the oldest example of symbiosis between dinosaurs and arthropods.

“Finding feather portions was already exciting,” says at the University of Oxford Museum of Natural History, but the discovery of the remains of beetle larvae among the feather fragments “was an incredible surprise”.

“Direct evidence of interactions between arthropods and vertebrates is exceedingly rare in the fossil record,” says PĂ©rez-de la Fuente.

The amber was found in Spain and dates back to the Cretaceous period. The precise species of dinosaur the feathers belonged to is unclear, but the plumage matches what palaeontologists expect of theropod dinosaurs like Velociraptor and ancient birds.

At first, PĂ©rez-de la Fuente and his colleagues couldn’t be sure that the association between the dinosaur feathers and beetle larvae was anything more than accidental as the tree sap that hardens into amber encases any material in its path.

On close examination, however, the researchers were able to pick out evidence that the beetle larvae were feeding on the dinosaur feathers. Inside the amber, the feathers weren’t pristine – they had been damaged and degraded before being enclosed. There were also faecal pellets created by the larvae among the feathers, says PĂ©rez-de la Fuente.

While there are insects that live and feed on birds as parasites, says PĂ©rez-de la Fuente, the story behind the Cretaceous dinosaur feathers and the larvae is different.

The larvae in the amber lack the critical features that would indicate they were living on the dinosaurs, such as specialised mouthparts for feeding on skin or blood, say the researchers. Instead, they suggest the beetle larvae were living and growing in the nest, making the most of what the dinosaurs shed. The researchers propose this as a case of a mutualistic relationship, with the larvae gaining a meal while also acting as a cleaning crew for the dinosaurs.

The insect larvae fossils appear to belong to a group of beetles with species alive today, say the researchers. Called dermestids, or skin beetles, some current species have larvae that live in bird nests and consume moulted feathers.

“The study presents fairly compelling evidence that Cretaceous-age dermestid beetles took advantage of that food source, especially since dermestids are found in present-day nests and areas where shed feathers accumulate,” says palaeontologist .

at the Royal Belgian Institute of Natural Sciences says the finding unveils one of the “earliest dino-arthropod interactions, which are very hard to document in fossils”.

A treasure trove of fossil nests uncovered in India hints at an array of as-yet-undiscovered dinosaurs belonging to the titanosaur group, and gives clues to how these animals reproduced.

A total of 92 nests and 256 eggs, measuring up to 20 centimetres long, were found in the Lameta Formation, a sequence of rock layers well-known for containing fossils of immense, long-necked dinosaurs called titanosaurs. Palaeontologists had previously identified three titanosaur species from bones found in this area.

at the University of Delhi and his colleagues discovered the nests during fieldwork between 2017 and 2020. The team proposes that there are at least six egg shapes – technically called oospecies – found in the formation. If each egg shape was laid by a different species, it would double the known number of species in the formation.

The nests also underscore what palaeontologists are coming to understand about how some of the largest dinosaurs reproduced. The nests were made up of egg clutches laid in shallow pits, much like those of modern crocodiles. And while the number of nests found close together indicate that these dinosaurs gathered to lay eggs, just like many modern birds, the nests are so close to each other that there was no room for the adults to stick around. This suggests these dinosaurs employed a “lay ‘em and leave ‘em” strategy like that of some sea turtles, where the next generation was left to hatch and wander out onto the landscape on their own.

at the University of Calgary in Canada, who wasn’t involved with the study, urges caution on taking the six different egg types as a sign of six different species. Larger or smaller individuals of the same species might lay eggs that superficially seem different, or different species might lay eggs that are indistinguishable, she says.

Finding bones and eggs together will provide firmer evidence of how many dinosaur species were around, says Zelenitsky. “That said, there is clearly something interesting about the Lameta Formation to consistently produce a number of different titanosaur egg types,” she says.

Back in the heyday of the dinosaurs, this part of western India was a wet and marshy lowland dotted with small lakes. “The flats offered sites close to water sources, soft soil for nest burial and possible availability of food for juveniles,” says Prasad, all of which would have made the area attractive to these dinosaurs.

These moist sediments also help explain why so many dinosaur nests came to be preserved in western India. When streams, marshes and ponds rose, nearby nests were inundated and buried.

Mammals survived the asteroid that wiped out the dinosaurs by evolutionarily hedging their bets, generating an array of varied species that set them up to weather the prehistoric apocalypse, according to a new analysis.

By looking at how ecosystems in prehistoric North America changed – or stayed the same – at the University of León, Spain, and his colleagues hoped to gain some insight into why mammals and other small creatures thrived after the impact while birds were all that remained of the dinosaurs.

“I do not believe that selectivity favouring small-bodied animals alone can explain the difference between survival and extinction between mammals and dinosaurs,” says García-Girón. The real picture is much more complex and has to do with the spread of different diets, behaviours and niches that animals had before the impact, he says.

Drawing on more than 1600 fossils of various North American dinosaurs, fish, amphibians, reptiles, birds and mammals, the team created an estimation of the niches each extinct species occupied. For each species, the researchers assigned a body size, habitat and diet, plugging this information into a computational model developed by ecologists to track how food webs shift over time.

The team found that dinosaurs present in North America 66 million years ago more or less resembled those of 18 million years earlier and represented a form of ecological stability. Mammals, meanwhile, persistently pushed the envelope of adaptation, evolving into a vast array of climbing, gliding, swimming, burrowing and other forms during this period.

Contrary to some that proposed a decline in the number of dinosaur species approaching the impact, the researchers found no such dip. If anything, dinosaurs like T. rex and Triceratops were filling the same roles their ancestors did millions of years earlier. Mammals, on the other hand, were more flexible.

“It not only amazed me how mammals managed to thrive in the highly complex, and probably dangerous, dinosaur-dominated ecosystems,” says García-Girón, but how also how rapidly our ancestors moved into vacant niches after the asteroid hit.

“Dinosaurs going extinct is certainly a captivating story, but they were just one of the many taxa that were dramatically affected by the
 mass extinction,” says Lucas Weaver at the University of Michigan. The study brings together the data various researchers have collected into a new theoretical model that can continue to be assessed with new discoveries, says Weaver, and such ecosystem-wide approaches are likely to provide the next big insights into what happened before and after this cataclysmic event.

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