- Jonathan Amos
- BBC science reporter
Scientists have unearthed the discovery of a well-preserved dinosaur leg.
The tip, covered in leather, is just one of a series of fascinating finds found at the Tanis Archaeological Site in North Dakota.
But it’s not just the condition of the pieces in there that catches the eye – what these ancient specimens represent to science is fascinating, too.
The main hypothesis of scientists is that the creatures found in Tanis were killed and buried on the day a giant asteroid struck the Earth.
On that day, 66 million years ago, the era of the dinosaurs ended and the appearance of mammals began.
Very few dinosaur remains have been found in the rocks that tell the story of the past millennia before the impact. It would be exceptional to have a sample from the time of the disaster itself.
The BBC spent three years filming in Tanis for a program that will be broadcast on 15 April on British television, narrated by environmental expert Sir David Attenborough.
Sir David will present the results, many of which will be made public for the first time.
In addition to the leg of the dinosaur, there are fish that breathed in the wreckage from the collision as it rained from the sky.
There is also the fossil of a turtle that was impaled by a wooden dowel; remains of small mammals and the burrows they made; Horned triceratops leather. The embryo of a flying pterosaur inside its egg; And what appears to be part of the asteroid itself.
“We find so many details on this site that tell us what happened moment by moment, it’s almost like watching it in the movies. You look at a rock pillar, you look at the fossils, and it takes you back to that day,” he says. Robert de Palma, a graduate student at the University of Manchester, UK, is leading the excavation at Tanis.
Currently, the idea that a space rock 12 kilometers wide hit our planet to cause another mass extinction is widely accepted.
The impact site was located in the Gulf of Mexico, off the Yucatan Peninsula. The place is located about 3000 km from Tanis, but the energy transmitted by the event was such that devastation was felt everywhere.
The archaeological site of North Dakota is a chaotic mess.
The remains of animals and plants seem to have been carried away in the sediment deposits by waves of river water caused by unimaginable earthquakes. Aquatic creatures mingle with terrestrial creatures.
Amidst the tangle of pieces, sturgeon and paddlefish fossils are essential. They have small particles stuck in the gills. They are globules of molten rock that were expelled by the impact that then fell on the planet. The fish could have inhaled the particles when they entered the river.
The pellets have been chemically and radiometrically linked to the Mexican impact site. And in two of the resin particles recovered from preserved trees, there are also small inclusions that imply extraterrestrial origin.
“When we realized there were impurities inside these tiny glass balls, we chemically analyzed them in the X-ray diamond synchrotron near Oxford,” explains Professor Phil Manning, PhD supervisor at DePalma in Manchester.
“We were able to separate the chemistry and determine the composition of this substance. All the evidence, all the chemical data from this study strongly suggests that we’re looking at a piece of the asteroid that ended everything for the dinosaurs.”
The existence of the Tanis site and the discoveries made about the site were first reported in The New Yorker in 2019. This caused an uproar at the time.
Science often requires that the initial presentation of new discoveries be made in the pages of an academic journal. A few peer-reviewed papers have already been published, and the excavation team promises more as they work through the painstaking process of excavating, preparing and describing fossils.
To present its television programme, the BBC invited outside experts to examine many of the findings.
Professor Paul Barrett of the Natural History Museum in London looked at the leg. He is an expert on ornithischian (mostly herbivorous) dinosaurs.
“It’s Thescelosaurus. It’s from a group for which we had no previous record of the shape of their skin, and it shows conclusively that these animals were very scaly like lizards. They weren’t as feathered as their carnivorous contemporaries.”
“It looks like an animal that just had its leg removed very, very quickly. No evidence of leg disease, no obvious diseases, no traces of leg extraction, like bite marks or parts of it missing,” he tells me.
“So our best idea is that this is an animal that died more or less instantly.”
The big question is whether this dinosaur actually died on the day the asteroid hit Earth, as a direct result of the catastrophe that followed. The team at the Tanis site think that’s very likely, given the tip’s location in the excavation deposits.
If so, it would be a great find.
But Professor Steve Busati of the University of Edinburgh says he remains a little skeptical – at least for now.
He worked as another external advisor to the BBC. He wants to hear the arguments made in the peer-reviewed articles, as well as the opinion of some paleobiologists with very specific disciplines to enter the site before they make their independent assessment.
Professor Pussat says it is possible, for example, that animals that died before impact were violently exhumed on the day and then reburied in such a way that their deaths appear simultaneous.
“These fish with spherical globules on their gills are an absolute calling card for the asteroid. But for some of the other claims — I would say they have a lot of circumstantial evidence that hasn’t been presented to the jury yet,” he says.
“For some of these discoveries, though, does it matter whether they died the day or previous years? A pterosaur egg with a baby pterosaur inside is extremely rare; there is nothing like it in North America. It doesn’t have to be all about the asteroid.”
There is no doubt that the egg of a pterosaur is distinctive.
Using modern X-ray technology, it is possible to determine the chemistry and properties of eggshell. It was likely made of leather rather than hard, which may indicate that the mother pterosaur buried the egg in sand or sediment like a turtle.
It is also possible, using X-ray tomography, to extract and print the bones of a young pterosaur and reconstruct the appearance of the animal. This is exactly what archaeologist de Palma did.
The small pterosaur was likely a species of azhdarchids, a group of flying reptiles whose adult wingspan could reach more than 10 meters from one end to the other.
De Palma gave a special talk about the discoveries in Tanis to the public at NASA’s Goddard Space Flight Center on Wednesday (06/04). He and Professor Manning will also present their latest findings to the General Assembly of the European Geosciences Union in May.
‘Dinosaurs: The Last Day with Sir David Attenborough’ will be broadcast on BBC One in the UK on 15 April.
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