How dinosaur vomit has solved these prehistoric mysteries
A new pterosaur species was recently discovered in the vomit of a dino. But that's just the start of revelations from prehistoric excretions.
One day 110 million years ago, in what’s now Brazil, a dinosaur had to get something off its chest. Small, pokey bones had massed inside the animal’s digestive tract, getting in the way of munching on fish and other snacks. The carnivore voided the stinky lump from its throat, just like modern owls jettison pellets of massed bone and hair from their small prey. Sediment eventually covered the blob. It fossilized and was encapsulated in stone until it was recently uncovered by paleontologists. Inside were the bones of a flying reptile no one had even seen before.
Time spent in the jaws and digestive system of a meat-eating creature was not kind to its meal’s skeleton. Despite their rough journey into the fossil record, however, the bones (mostly jaws and teeth) were well-preserved enough to tell they belonged to an unexpected species of pterosaur that sieved ancient waters for tiny creatures much the way flamingos do today. Universidade Federal do Rio Grande do Norte paleontologist Aline Ghilardi and her colleagues named the pterosaur Bakiribu waridza when they described the find earlier this year.
“This was not just a fossil concretion containing a new species of a rare type of pterosaur, but an exceptional ichnofossil, a regurgitalite,” Ghilardi says.
Regurgitalites and other fossils of digestive contents fall under a broader category of fossils called bromalites. While they might sound gross, excreted masses cast off by dinosaurs and other prehistoric organisms offer direct insight into what living things were eating, how their internal organs work, and how long-lost species actually interacted with each other in ancient ecosystems.
Is it porridge or a pterosaur?
In the case of Bakiribu, the pterosaur’s discovery was fortuitous. “When my student William first showed me the concretion and asked what it was, I had an unusual stroke of luck,” Ghilardi says. She had just been reading about Pterodaustro, a pterosaur found in the rocks of Argentina and Chile with jaws of thin, closely-packed teeth that allowed the flier to filter-feed in prehistoric ponds. The jaws in the concretion looked very similar, only in a very different place. No pterosaur like this had been found in rocks of the same age within Brazil before. Ghilardi and colleagues immediately knew that the bones represented something new.
But why did the bones look so messy? “I joked that it looked like someone had spot out a kind of porridge, and ‘Mingau,’” meaning porridge in Portuguese, “quickly became the fossils nickname,” Ghilardi says. While fossils are sometimes found within concretions that form after burial, layers of rock layering around a central nucleus of tooth or bone, Mingau was something else. The fragmented nature of the bones, the fish fossils, and the closely-packed nature of the remains indicated that the mass had been ejected from a larger animal—likely a predatory dinosaur.
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“It’s definitely an unusual pathway to take and end up as a fossil,” says University of Tennessee Knoxville paleontologist Stephanie Drumheller-Horton, who was not involved with the study. And, fortunately for Ghilardi and her colleagues, the pterosaur bones were not too damaged by their trip inside the predator. “Partial digestion and regurgitation can add some unusual complications to the mix like acid etching, whatever mechanical processing occurred as the prey was caught and consumed,” she adds, which no doubt made Bakiribu look like porridge.
Had the pterosaur not been eaten and subsequently thrown back up, paleontologists may never have learned Bakiribu existed. More than that, Ghilardi says, “regurgitalites can provide rare ecological insights.” The fossils represent relationships between organisms, she notes, placing them within the same environment at the same time and offering clues to interactions that are otherwise invisible to experts. Given that fossil rock formations can often span 10 million years or more, having fossils that place an organism and its food in the same place, at the same time, can act as a window to the actual food webs that connected prehistoric species.
In one end, out the other
While scientists have only been recently making new, stunning finds from dinosaur vomit globs, bromalites ejected from the other end of prehistoric animals have had a long history of study within paleontology.
Paleontologists have been fascinated by the excretions of prehistoric reptiles since the 19th century. English paleontologist William Buckland was fascinated with the fossilized feces of prehistoric creatures, commonly known as “Bezoar Stones” but scientifically termed coprolites. These specimen often contain teeth, scales, and other hard parts of whatever the predators had been eating in the area. Around 1840, Buckland commissioned a table inset with 330 million-year-old coprolites, a paleontological in-joke when visitors came calling. Today, it remains notorious as “Dr. Buckland’s Poo Table” at the U.K.’s Lyme Regis Museum.
Paleontological potty humor aside, though, Buckland and other experts immediately recognized the importance of such fossils to reconstructing the lives of prehistoric animals. A coprolite or regurgitalite can tell us more about how an ancient animal really lived than even the most complete skeleton.
One particularly large coprolite attributed to Tyrannosaurus rex, for example, shows that the giant carnivore was not shy about ingesting broken pieces of bone and had such a fast-running digestive system that identifiable muscle could still be seen in the prehistoric poop, consistent with a warm-blooded animal that had to eat often.
(Forget poop. Here’s the surprising science of dinosaur pee.)
What’s on dinosaurs’ secret menus
Alone, coprolites, regurgitalites, and other bromalite fossils can sometimes indicate what a particular animal was eating, or what species were being eaten. But in places where bromalites are preserved in abundance, they can track sweeping ecological shifts over millions of years. In the Triassic and Jurassic rocks of Europe’s Polish Bain, paleontologists have found an abundance of bromalites left behind by various dinosaurs 200 to 230 million years ago. By looking at the contents of the bromalites and other geological details, Uppsala University paleontologist Grzegorz Niedźwiedzki and his colleagues were able to track how dinosaurs—and their dining habits—evolved over time.
Among reptiles thought to be close to the first dinosaurs, called silesaurs, coprolites contained “ a wealth of curious organic remains,” Niedźwiedzki says. Inside, X-rays revealed, were “the remains of tiny beetles, lots of beetles,” he notes, along with bits of plants and fish. “They were willing to eat anything they encountered,” Niedźwiedzki says, an omnivorous diet that may have helped set dinosaurs up for later success.
Just above the silesaurs and their droppings in the rock layers, paleontologists found later fossils of true dinosaurs—and their poop, too. Their coprolites indicated that the small, early ancestors of dinosaurs like T. rex were fish-eaters, while the predecessors of later giants like Apatosaurus were omnivores.
Dinosaurs eventually diversified into omnivores, herbivores, and carnivores at small sizes throughout the Triassic, and climate shifts about 208 million years ago set a new menu. Earth’s climate was becoming warm and wet, more humid and less arid than it had been earlier in the Triassic, which favored the spread of tree-sized seed ferns, cycads, ginkgoes, and many other nutritious plants.
The bromalite evidence indicates that herbivorous dinosaurs were taking advantage of this rich Triassic salad bar, becoming larger in size, as carnivorous dinosaurs became larger to prey upon the large herbivorous species. Vigorous plant growth opened the possibility for herbivores to become larger and, in turn, carnivorous dinosaurs hunted the small offspring of the big herbivores and scavenged upon the multi-ton carcasses of the adults.
“We were surprised that so many coprolites contained bone fragments,” Niedźwiedzki says of the carnivorous droppings, as “this suggests that some of the predators were eating the crushed bones and trying to extract everything, all the nutrients, that they could.” Paired with research on ancient climate shifts, the bromalites document how dinosaurs ate their way through the ancient world and diversified into the broad array of shapes and sizes that emerged later in the Jurassic.
Insights into ancient stomachs
Bromalites can help experts outline the inner workings of prehistoric organisms as well as how they related to their outer environments. In 2022 researchers described a pair of fossilized pellets, found in the Jurassic rocks of China and associated with the skeletons of a pterosaur known as Kunpengopterus. Each of the pellets was packed with fish scales. They were apparently regurgitated for the same reason predatory birds eject hard-to-digest parts of their meals, just like the regurgitalite that preserved Bakiribu.
The fact the pterosaurs could produce the pellets indicates that they their stomachs were divided into two parts, a forward part that oozes stomach acid to begin to break down food before passing into a more muscular portion equivalent to the gizzard in birds. No one has found the fossilized remains of a pterosaur digestive system to date—such soft organs typically decay away long before any chance of fossilization. But studying the pellets has revealed some of the invisible details of how the reptiles’ digestion would have worked.
Of course, association is important to teasing out these connections. “If the fossils were found in that animal’s gut tract, it ate those things,” says Drumheller-Horton of bromalites found with or within skeletons. Individual coprolites and regurgitalites are harder to match with what made them unless both were fossilized together. Each piece is part of a very intricate puzzle that requires experts to dig into how the fossil formed.
Paleontologists (and perhaps readers) will undoubtedly still have a gas joking about bromalites. A favorite paleontological practical joke is to present students with a selection of fossils to touch only to reveal after the fact that one is a bromalite. But alongside the humor, the science is getting more serious.
Bromalites are not just fossils, but represent soft tissues, behavior, and ecological connections that bones alone may not reveal. “Just a few years ago, these types of fossils were the butt of jokes and brough a smile to the faces of many colleagues,” Niedźwiedzki says. “This changed quite quickly when it turned out that coprolites contained preserved elements that would be almost impossible to find otherwise,” he notes, clues wrapped up in exceptional excreta.
