A group of scientists presented an astonishingly preserved dinosaur leg. The limb, complete with skin, is just one of a series of remarkable finds emerging from the site of Tanis, in the state of North Dakota (USA).
But it’s not just their exquisite condition that’s striking, but also what these ancient specimens may represent.
Scientists believe the Tanis creatures died and were buried the same day as a giant asteroid hit the earth.
He was the day 66 million years ago the reign of the dinosaurs ended and the rise of mammals began.
Very few dinosaur remains have been found in rocks that even record the last thousands of years before impact. To have a specimen of the cataclysm itself would be extraordinary.
The BBC spent three years filming a show in Tanis which will air on April 15, narrated by David Attenborough.
Attenborough will review the finds, many of which will be seen in public for the first time.
Next to the leg there is fish that breathed in impact debris as it rained from the sky.
Also seen are a fossil turtle rammed with a wooden stake, the remains of small mammals and the burrows they dug, the skin of a horned triceratops, the embryo of a flying pterosaur inside its egg and what appears to be a fragment of the pterosaur itself asteroid.
“We have so many details on this site that tell us what happened at every moment, it’s almost like seeing it in the movies. You look at the column of rock, you look at the fossils there, and it takes you back to that day,” said Robert DePalma, a University of Manchester graduate student who is leading the Tanis excavations.
It is now widely believed that a space rock about 12 kilometers wide hit our planet and caused the last mass extinction.
The impact site was identified in the Gulf of Mexico, off Chicxulub (Yucatan Peninsula). It’s about 3,000 kilometers from Tanis, but the energy of the event was such that its devastation was felt everywhere.
The North Dakota field is a chaotic mess.
Animal and plant remains appear to have been swept away on a sediment dump by waves of river water caused by unimaginable earthquakes.
Aquatic organisms mingle with terrestrial creatures
The sturgeons and paddlefish of this tangle of fossils are essential. They have small particles trapped in their gills. It was the molten rock spheres ejected by the impact that then fell all over the planet.
Scientists believe that the fish breathed in the particles when they entered the river.
The spherules have been linked chemically and by radiometric dating to the impact site in Mexico, and in two of the preserved tree resin particles recovered there are also small inclusions which have a extraterrestrial origin.
“When we noticed that there were inclusions inside these small glass spheres, we chemically analyzed them at the Diamond X-ray synchrotron near Oxford,” explained Professor Phil Manning, thesis supervisor. From Palma to Manchester.
“We were able to separate the chemistry and identify the composition of this material. All of the evidence, all of the chemical data in this study strongly suggests that we look at a piece of the asteroid that killed the dinosaurs“, he added.
The existence of Tanis and the claims made about this place were first made public by the magazine the new yorker in 2019, which was all the rage at the time.
Science often demands that the initial presentation of new discoveries be made in the pages of an academic journal. A few peer-reviewed articles have been published, and the excavation team promises many more during the meticulous process of extracting, preparing and describing the fossils.
To make its TV show, the BBC brought in outside experts to review several of the findings.
Professor Paul Barrett of the Natural History Museum in London and an expert on ornithischian (mainly herbivorous) dinosaurs have studied the leg.
“It’s a Thescelosaurus. It comes from a group for which we had no prior record of what their skin looked like, and it shows very conclusively that these animals were very scaly, like lizards. They didn’t have feathers like their carnivorous contemporaries,” he said.
“It looks like an animal that has just had its leg ripped off very quickly. There is no evidence of disease in the leg, there are no obvious pathologies, there is no evidence that the leg was pulled, like bite marks or parts of it that disappeared,” he said.
“So the strongest idea we have is that this it is an animal that died more or less instantly“, he added.
The big question is whether this dinosaur actually died the day the asteroid hit as a direct result of the ensuing cataclysm.
Tanis’ team thinks this is most likely the case, given the position of the limb in the excavation sediments.
If so, that would be quite a discovery.
Professor Steve Busatte of the University of Edinburgh has argued that I’m a little skeptical at the moment.
Busatte, who was another external consultant to the BBC, wants to see the arguments put forward in more peer-reviewed papers, and for paleoscientists with very specific specialties to come to the site to give their independent assessment.
The expert said it is possible, for example, that animals that died before impact were dug up by the violence of the day and then put back on the ground, so that their deaths appear simultaneous.
“These fish with spherules on their gills are an absolute calling card for the asteroid. But for some of the other statements, I would say they have a lot of circumstantial evidence that has not yet been presented to the jury“, he assured.
“However, for some of these discoveries, does it matter whether they died the day before or in previous years? The pterosaur egg with a baby pterosaur inside is super rare; there is nothing like it in north america. Not everything has to be about the asteroid.
Thanks to modern x-ray technology, it is possible to determine the chemistry and properties of the eggshell. It was probably leathery rather than hard, which may indicate that the pterosaur mother buried the egg in sand or sediment, as turtles do.
It is also possible with X-ray tomography to virtually extract the bones of the pterosaur chick inside, print them out and reconstruct what the animal would have looked like. DePalma did.
The baby pterosaur was likely a type of azhdarchid, a group of flying reptiles whose adult wings could reach over 10 meters from tip to tip.
On Wednesday, DePalma gave a special lecture on Tanis’ findings to an audience at the US space agency NASA’s Goddard Space Flight Center. He and Manning will also present their latest data at the General Assembly of the European Geosciences Union in May.
By Jonathan Amos
BBC News World