Scientists have revealed the discovery of an incredibly well-preserved dinosaur leg.
The limb, complete with skin, is just one of a series of remarkable finds recovered at the Tanis archaeological site in North Dakota.
But it’s not just the condition of the pieces found there that draw attention — what these ancient specimens represent for science is also quite remarkable.
Scientists’ main hypothesis is that the creatures found on Tanis were killed and buried the day a giant asteroid hit Earth.
It was on that day, 66 million years ago, that the reign of the dinosaurs ended and the rise of mammals began.
Very few dinosaur remains have been found in the rocks that tell the story of the last few thousand years before the impact. And to have a specimen from the time of the cataclysm itself would be extraordinary.
The BBC spent three years filming in Tanis for a program to be broadcast on 15 April on British television, narrated by environmentalist Sir David Attenborough.
Sir David will present the findings, many of which will have their first public display.
In addition to the dinosaur leg, there are fish that breathed in the debris from the impact as it rained from the sky.
There is also a fossil of a turtle that was impaled by a wooden stake; the remains of small mammals and the burrows they made; skin of a horned triceratops; the embryo of a flying pterosaur inside its egg; and what appears to be a fragment of the asteroid itself.
“We find a lot of details on this site that tell us what happened moment to moment, it’s almost like seeing it happening in movies. You look at the rock column, you look at the fossils, and it brings you back to that day,” he says. Robert DePalma, a graduate student at the University of Manchester, UK, who is leading the excavation at Tanis.
Currently, the idea that an approximately 12 km wide space rock hit our planet to cause the last mass extinction is widely accepted.
The impact site has been identified in the Gulf of Mexico, off the Yucatan Peninsula. The place is about 3,000 km from Tanis, but the energy transmitted by the event was such that its devastation was felt everywhere.
The North Dakota archaeological site is a chaotic mess.
The remains of animals and plants appear to have been transported in a sediment deposit by waves of river water triggered by unimaginable earthquakes. Aquatic organisms are mixed with terrestrial creatures.
Amidst the tangle of pieces, fossils of sturgeon and oarfish are fundamental. They have tiny particles stuck in their gills. They are spherules of molten rock expelled by the impact that then fall back to the planet. The fish would have inhaled the particles as they entered the river.
The spherules were chemically and radiometrically linked to the Mexican impact site. And in two of the recovered resin particles from preserved trees there are also small inclusions that imply an extraterrestrial origin.
historical piece
“When we realized that there were inclusions inside these tiny glass spherules, we analyzed them chemically in the Diamond X-ray synchrotron near Oxford,” explains Professor Phil Manning, who is DePalma’s PhD supervisor in Manchester.
“We were able to separate the chemistry and identify the composition of this material. All the evidence, all the chemical data from this study strongly suggests that we are 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 publicized in the New Yorker Magazine in 2019. This caused a stir 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 much more as they work through the painstaking process of extracting, preparing and describing the fossils.
To make its TV show, the BBC invited outside experts to examine several 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 a Thescelosaurus. It’s from a group that we had no previous record of what its skin looked like, and it shows very conclusively that these animals were very scaly like lizards. They weren’t feathered like their carnivorous contemporaries.”
“It looks like an animal whose leg was just ripped off very quickly. There’s no evidence on the leg of disease, there’s no obvious pathologies, there’s no traces of the leg being pulled out, like bite marks or pieces of it that are missing,” he tells me.
“So the best idea we have 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 cataclysm that followed. The team at the Tanis site thinks it very likely so, given the limb’s position in the excavation sediments.
If that’s the case, it would be a great find.
But Professor Steve Busatte of the University of Edinburgh says he’s still a little skeptical — at least for now.
He acted as another external consultant to the BBC. He wants to hear the arguments presented in peer-reviewed articles, as well as the opinion of some paleoscientists with very specific specialties who come to the site before making their independent assessment.
Professor Busatte says it’s possible, for example, that animals that died before the impact were exhumed by violence on the day and then reburied in a way that made their deaths appear to be simultaneous.
“These fish with spherules 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 if they died the day or years before? The pterosaur egg with a baby pterosaur inside is super rare; there’s nothing like it in North America. Not everything has to be about the asteroid. “
There is no doubt that the pterosaur egg is special.
With modern X-ray technology it is possible to determine the chemistry and properties of the eggshell. It was likely leathery rather than hard, which may indicate that the mother pterosaur buried the egg in sand or sediment like a turtle.
It is also possible, with X-ray tomography, to virtually extract the bones of the baby pterosaur, print them and reconstruct the animal’s appearance. Archaeologist DePalma did just that.
The baby pterosaur was likely a type of azhdarchid, a group of flying reptiles whose adult wings could reach over 10 meters from end to end.
DePalma gave a special talk about the discoveries at Tanis to an audience at NASA’s Goddard Space Flight Center on Wednesday. He and Professor Manning will also present their latest findings to the General Assembly of the European Geosciences Union in May.
“Dinosaurs: The Final Day with Sir David Attenborough” will be broadcast on BBC One in the UK on 15 April.
