Quartz crystals in the stomach of fossil birds complicate the mystery of his diet

It is difficult to know what the life of prehistoric animals was like – even answering seemingly simple questions, such as what they ate, can be a challenge. Sometimes paleontologists are lucky, and pristine fossils preserve the stomach contents of an animal or give other clues. In a new study in Boundaries in Earth Science, researchers found the fossil of a bird that lived next to the dinosaurs got more questions than answers when they found quartz crystals in the bird’s stomach.

“I would say it’s a kind of strange form of soft tissue preservation we’ve never seen before,” says Jingmai O’Connor, co-curator of fossil reptiles at Chicago’s Field Museum. “Finding out what’s in the bird’s stomach can help us understand what it ate and what role it played in its ecosystem.”

“This article tells us that the Enantiornithes, one important group of fossil birds, still have no direct stomach tracks or evidence,” says Shumin Liu, a student at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and the first article of the article author. “I was excited, it’s a breakthrough for them.”

The fossil bird that the researchers focused on is a specimen of Bohaiornis guoi. “They are part of an early generation of Cretaceous birds, about 120 million years ago,” said O’Connor, who worked at the newspaper while at IVPP, where Liu was her master’s student. “They still hold teeth and claws on their hands, but they are small, as big as a dove, so they are not scary.” Bohaiornis were part of a group called the enantiornithines that were once the world’s most common birds; Thousands of enantiornithine samples were found in northeastern China from the Jehol group deposits.

Despite the large number of finely preserved enantiornithines, no one was preserved with traces of food in their stomachs that researchers could tell what these birds ate. “We can identify the diet and reconstruct the digestive system for all these other groups of birds that occur in the deposits that take up the Jehol Biota, in addition to the enantiornithines, even though you have more enantiornithines than any other group,” says O’Connor. “For these guys, we have no copies or evidence of diet, which is really weird.” However, in the copy that O’Connor and her colleagues examined in this new article, there was an idea: a previous study pointed to the presence of small rocks in the stomach.

Many live birds have an organ called the peritoneum – a thick, muscular part of the stomach helps them digest food. They swallow small rocks, gizzard stones, and these rocks drive to the gizzard, where they help to crush difficult food. These gizzard stones, called gastrolites, have been found in some dinosaurs and bird fossils, giving clues as to what those animals ate – they are associated with diets of sticky plant material and seeds.

But rocks in the stomach of an animal are not necessarily a sign that he is using them to crush food. Some modern birds of prey swallow rocks called, to help remove material from their digestive tract to clean it. And sometimes rocks were found near the stomach cavities of dinosaur fossils that accidentally swallowed the animal, or the stones happened to be near the fossil. “You have to distinguish between just a gastrolite and a gastrolite used as a gizzard stone,” says O’Connor.

Although there is no clear evidence of gastrolytes in the enantiornithine birds, a specimen of a specimen of Bohaiornis guoi contains rocks in its stomach that are used as rattle (gastrolytes ingested by birds of prey to clean the stomach but not to digest food). O’Connor was skeptical; the photos of the rocks do not look right. Gastrolytes are usually made from different types of rock and have slightly different colors and shapes; these rocks were all similar to each other and to the petrified bone itself. They also did not appear to be properly formed or grouped – they were too round and scattered. “I did not know what it was, but I was like gastrolites,” she says. Therefore, she and her colleagues decided to find out what these rocks are and compare them to gastrolytes from other fossils and dinosaurs.

The researchers took a sample of the rocks in Bohaiornis’ stomach and examined it under a scanning electron microscope. They then exposed the rocks to X-rays to determine what wavelengths the rocks had absorbed. Since each mineral absorbs different wavelengths, it has helped the researchers narrow down what these rocks are made of.

“We found that the pieces of rock called gastrolytes were chalcedonic crystals,” says O’Connor. “Chalcedony is basically quartz crystals that grow in sedimentary rocks. There was no evidence of this in the Jehol yet, but there is a lot of evidence of it in the fossil record where chalcedony crystals will form in a clamshell, or sometimes chalcedony will be the minerals that the bones in a fossil form. ‘What’s more, the chalcedony was interconnected in one thin sheet of crystal, rather than separate rocks that swallowed the bird.

The amount of chalcedony present was also incorrect when used to aid digestion. Scientific literature suggests that the rocks that birds consume as a rattle make up about 3% of their body mass; Since Bohaiornis was probably about 300 grams, the team would be looking for a ring of up to 9 grams. O’Connor says, “We could not extract the whole sample and find out how much it weighed, but Shumin was really smart and she took a piece of chalcedony that weighed 3 grams, and it was large” – much larger than the joint size of the pieces of chalcedony in Bohaiornis’ stomach.

The combined evidence suggests that Bohaiornis did not have gastrolytes to help crush food or to stomach. Or, at least, this specimen of Bohaiornis does not contain the gastrolites.

“We only have this absence of evidence, and paleontologists always say that absence of evidence is not evidence of absence. But I am always opposed to whoever came up with the proverb, never thought he had thousands of copies that were complete. and articulated, some retain soft tissue, “says O’Connor. If early chalk enantiornithines did use gastrolytes, it is terribly strange that none of the thousands of fossils show it.

O’Connor notes that although none of the enanthiornithine birds of the Jehol Formation have evidence of stomach contents, there is one from Spain with pieces of freshwater shellfish in its stomach. But the mystery of what Bohaiornis ate, and why none of the Jehol enantiornithines had anything in their stomachs, remains.

“This study is important because this fossil is the only fossil record of Enantiornithes containing possible gastrolytes, even possible real stomach tracks in the Jehol. What’s more, only these clade fossil birds have no stomach tracks so far, while most other clades have these tracks, ‘says Liu.

“We’re always trying to find evidence, and the samples that are proposed to fill this gap unfortunately just do not,” O’Connor says. “It’s just part of the paleo game, part of science – to constantly correct. I’m glad if we do not understand things, because it means there is research to do, it is exciting.”

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