Paleontologists have announced a first-of-its-kind fossil find from the Late Cretaceous rocks near Lusk with indications that an excellent discovery is likely waiting to be unearthed in eastern Wyoming.
New research published by scientists with the Oertijdmuseum in the Netherlands reveals the first dinosaur eggshell ever found in the Lance Formation of eastern Wyoming. The fossilized piece of dinosaur egg is smaller than a postage stamp, but it has enormous and tyrannical implications.
Jonathan Wallaard, the senior curator of the Oertijdmuseum in the Netherlands, isn’t putting all his eggs in one basket (yet), but he believes this eggshell indicates a nursery could be buried somewhere in eastern Wyoming.
Furthermore, the occupant of this might have been none other than the Tyrant Lizard King, Tyrannosaurus rex.
“This single fragment shows us the preservation of eggshell in the Lance Formation, and the possibility of (dinosaur) nests in eastern Wyoming,” Wallaard told Cowboy State Daily. “Hopefully, this will help with the discovery of more fragments, and maybe even complete eggs, of Tyrannosaurus rex.”
Shell Sieving
The eggshell fragment was found in a “prolific microsite” in the Lance Formation near Lusk in 2022. The Oertijdmuseum has been excavating the site every summer for several years, finding tiny fossils from mammals, fish, turtles, crocodiles, and dinosaurs from the Late Cretaceous Period.
“A microsite is an area where all kinds of small fragments are flushed together,” Wallaard said. “We’re working on several microsites to make complete reconstructions of the Late Cretaceous ecosystem, but that is a work in progress.”
Rather than finding one or two skeletons of massive dinosaurs, microsites yield much smaller but equally impressive discoveries of tiny bones and fragments from every animal that inhabited a prehistoric ecosystem.
Similar microsite work is ongoing at several Lance Formation sites at Triceratops Gulch near Glenrock. Excavations from over 70 sites on one ranch have produced fossils from nearly every known animal from the Lance Formation, and possibly some new species.
Oertijdmuseum scientists found the shell while sieving. It’s a process where dirt excavated from an archaeological or paleontological site is put on a screen and gently shaken, separating the loose sediment from the hardened artifacts.
“It was originally one piece, measuring around 8 millimeters,” Wallaard said. “We knew that it was a piece of eggshell, based on the structure of the fragments, visible to the naked eye, which is the reason why we took the fragment with us.”
The eggshell was “originally” one piece because the 8-millimeter-wide eggshell has since been broken into four pieces. It sounds sacrilegious, but it was deliberately broken so it could be thin-sectioned and examined by a Zeiss Axio Scan, a high-powered microscopy slide scanner.
“After making the thin sections, we could see the cell structure and the typical features found in the structure of eggshell,” he said. “Based on the structure of the fragments, we know this is a 67-million-year-old dinosaur eggshell.”
What's Ovaloolithus?
Sometimes paleontologists find a definite fossil that can’t be assigned to any species or genus. To scientifically describe these specimens, they are assigned to a “form taxa” that identifies them as what they are, whether it’s a footprint, a skin impression, or an eggshell.
Eggshells can be found at dinosaur sites worldwide, but intact eggs and nests are quite rare. The only way to conclusively attach a dinosaur species to a dinosaur egg is to find an intact embryo inside, and even that can be like walking on eggshells.
In the new paper, the Lance Formation eggshell was described as an “oofossil” belonging to the ootaxa Ovaloolithus. It’s not as exciting as “the first T. rex eggshell,” but that’s about as specific as any paleontologist would dare to go with such a tiny fragment.
Based on their analysis, Wallaard and his researchers concluded that the eggshell “can tentatively be ascribed to either ornithopod or non-avian theropod dinosaurs,” but was absolutely from a dinosaur egg. It’s definitely Ovaloolithus.
Ovaloolithid ootaxa have been found in the Late Cretaceous rocks of Utah, but this eggshell fragment is distinctly different from what’s been found before. Wallaard said they have a hunch of what hatched out of that egg, making the already-exciting fossil even more extraordinary.
Big Chicken, Big Egg Situation
After studying the external and internal structure of the eggshell, the researchers observed that it’s notably different from the well-studied eggshells of duck-billed dinosaurs, such as Maiasaura and Saurolophus, species with an abundance of identified eggs, nests, and eggshell fragments.
The eggshell’s structure is also different from the well-studied eggs of Protoceratops, a Mongolian relative of Triceratops. A 2020 paper found that Protoceratops eggs had soft, leathery shells, similar to those of modern-day turtles and lizards, unlike the hard-shelled eggs of modern birds.
“This type of eggshell has not previously been found in the USA,” Wallaard said. “It’s only known from Asia, where a lot of eggs of this type have been found and assigned to Tarbosaurus.”
Tarbosaurus, a massive Late Cretaceous theropod, is only found in China and Mongolia. Despite being a distinctly different dinosaur, it could pass as a perfect doppelganger for Tyrannosaurus.
Wallaard said this eggshell’s similarity to Tarbosaurus eggs strongly indicates that it came from a theropod egg. While admitting that it’s “highly speculative,” the similarity of Tarbosaurus and Tyrannosaurus suggests this egg was laid by the King of the Cretaceous — or its controversial cousin.
“Without an embryo, it is always educated guessing,” he said. “That is why the abstract is inconclusive, but it’s very likely that this eggshell belonged to either T. rex or Nanotyrannus.”
Egg-Site-ing Discovery
If finding a potential T. rex eggshell wasn’t exciting enough, Wallaard believes there’s more where that came from. The edges of the fossilized eggshell reveal more than one might think.
“The fragment was square, and not rounded,” he said. “Since the fragment was not rounded at all, we assume that it wasn’t transported very far.”
Fossilized remains are typically buried after being transported by water. The rounder the edge, the further it tumbled and traversed through a flowing creek or river before being buried, just like the smooth, rounded rocks found on a beach.
The sharp edges of this eggshell fragment tell Wallaard that the eggshell didn’t go far before it was buried. That leaves one crucial question: how far is “not very far?”
“It could be a few miles or even 100 miles away,” he said. “We don’t know how strong those fragments were prior to fossilization. What this single fragment shows us is, at least, the probability of nests nearby.”
Nobody’s ever found an intact dinosaur egg in the Lance Formation, let alone an entire T. rex nest. Wallaard expects the Tyrant Lizard King would have been highly secretive and solitary when nesting, making the already low chances of finding a rex nest even lower.
“Large carnivorous dinosaurs are often cannibalistic, which makes it unlikely that they nested together, so it will not be a big nesting site,” he said. “However, it’s likely that the nesting site this eggshell came from was nearby.”
Big Easter Egg Hunt
Since the discovery of the eggshell, Wallaard and his colleagues have been scouring eastern Wyoming for a trail that could lead them to the discovery of a lifetime: a T. rex nest with intact eggs and embryos. Finding it will be a tough egg to crack.
They’ve found plenty of other fossils during their search, including an articulated Edmontosaurus skeleton and the partial skeleton of a young Triceratops, Wyoming’s state dinosaur. However, the T. rex nest still eludes them.
“We hope to find an egg site nearby,” he said. “So far, no luck, but we are still looking.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
