IMAGE: Reconstruction of the bohaiornithid Sulcavis, close relatives of Bohaiornis guoi, insect hunting. view more
Credit: © S. Abramowicz, Dinosaur Institute, Los Angeles County Museum of Natural History.
It’s hard to tell what the life of prehistoric animals was like – even answering seemingly simple questions, how they would eat, can be challenging. At times, paleontologists get lucky, and pristine fossils preserve the stomach contents of an animal or provide other clues. In a new study in Boundaries in Earth Science, researchers studying a bird fossil living next to the dinosaurs found more questions than answers when they found quartz crystals in the bird’s stomach.
“I’d say it’s a kind of weird type of soft tissue preservation that we’ve never seen before,” says Jingmai O’Connor, the fossil reptile link curator at the Chicago Field Museum. “Finding out what this bird’s stomach is in can help us understand what it has eaten and how it has played a part in its ecosystem. ”
“This paper tells us that there are no direct finds or evidence of the Enantiornithes, one important cover of fossil birds,” says Shumin Liu, a student at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and the first in the author’s paper “I was excited, it’s a disappointment about them.”
The fossil bird that the researchers focused on is an example of Bohaiornis guoi. “They’re part of an early line of birds from the Cretaceous, about 120 million years ago,” said O’Connor, who worked on the paper while at IVPP, where Liu na a student of his Master. “They still hold teeth and claws on their hands, but they are small, about the size of a pigeon, so they are not particularly terrible. “Bohaiornis was part of a group called the enantiornithines that were once the most common birds in the world; thousands of samples of enantiornithine were found in the deposits of Jehol Group in northeastern China.
Despite the large number of well-preserved enantiornithines, none of them were preserved with stomach food markers that could tell researchers what these birds would eat. “We can identify the diet and rebuild the digestive system for these other bird groups found in the deposits that record Biota Jehol, except the enantiornithines, even if you have more enantiornithines than any other group. “For these people, we don’t have samples or preserved evidence on diet, which is very strange.” In the sample that O’Connor and her colleagues studied in the In this new paper, however, there was a hint: a previous study showed that small rocks were in the stomach.
Many living birds have an organ called gizzard – a thick muscular part of the stomach helps them digest food. They swallow small rocks, called gizzard stones, and these rocks make their way to the chisel, where they help crush hard food. These gizzard stones, called gastroliths, have been found in some dinosaur and bird fossils, testifying to what these animals ate – they have been linked to a strict plant-based diet and seeds .
But rocks in an animal’s stomach are not a sign that it is being used to digest food. Some modern day birds of prey swallow rocks called rangle to help release material from their digestive tract to clean it up. And sometimes, rocks were found near the stomach caves of dinosaur fossils that the creature accidentally swallowed, or the stones were just coincidental near the crown. “You have to differentiate between just gastrolith and gastrolith that is used as a gizzard stone,” O’Connor says.
Although there is no clear evidence of gastroliths in the enantiornithine birds, a paper published in 2015 concluded that a sample of Bohaiornis guoi the rocks of the stomach were used as rangle (gastroliths infused with spider mites to cleanse the stomach, but not to digest food). O’Connor was skeptical; the pictures of the rocks did not look right. Gastroliths are usually made of different types of rock and have slightly different colors and shapes; these rocks were all similar in shape to each other and to the fossil bone itself. They did not appear to be properly shaped or assembled – they were too round and too scattered. “I didn’t know what they were, but I was like, they’re not gastroliths,” she says. So she and her colleagues began to find out what those rocks were and compare them to gastroliths from other fossil birds and dinosaurs.
The researchers took a sample of the rocks in Bohaiornis’ stomach and examined them under a scanning electron microscope. They then exposed the rocks to X-rays to find out what waves the rocks caught. Since each mineral contains different waves, this helped the researchers to reduce the source of these rocks.
“We found that these rock fragments were called chalcedony crystals called gastroliths,” O’Connor said. “Chalcedony is essentially quartz crystals that grow in sedimentary rocks. There was no evidence of this in the Jehol but there is ample evidence of it inside the fossil record where crystals of chalcedony form inside a clamshell, or sometimes chalcedony replaces minerals that make up the bones in fossils. ” Moreover, the chalcedony was all interconnected in a single thin sheet of crystal, rather than separate rocks that swallowed the bird.
The degree of chalcedony present was wrong, too, if it was used to aid digestion. Scientific literature suggests that the rocks that birds eat as rangle make up about 3% of their body mass; since Bohaiornis seemed to weigh about 300 grams, the team would look for a value of up to 9 grams of rangle. O’Connor says, “We couldn’t take out the whole sample and find out what the weight was, but Shumin was very subtle, and she took a piece of weighted chalcedony. 3 grams, and it was very large “–way larger than the total size of the pieces of chalcedony in the Bohaiornis stomach.
The combined evidence shows that Bohaiornis did not have gastroliths to help with the crushing of food or rangle to help cleanse her stomach after all. Or at least the gastroliths in this sample of Bohaiornis are not.
“We have this lack of evidence, and paleontologists always say that lack of evidence is not evidence of absence. But I will always oppose whoever came up with that adage. he never thought there were thousands of samples that are perfect and artistic, some retaining soft print, “O’Connor said. If early Cretaceous enantiornithines recruited gastroliths, it is strange that none of the thousands of fossils show them.
O’Connor notes that while none of the enantiornithine birds from the Jehol Creation show evidence of stomach contents, there is one from Spain with pieces of freshwater shellfish in the stomach. But the mystery of what Bohaiornis ate, and why none of the Jehol enantiornithines has anything in their stomachs.
“This study is important because this fossil is the only fossil record of Enantiornithes that contains potential gastroliths, even real stomach findings that may be present in the Jehol. this cover of fossil birds has no stomach traces to date, but most of these finds are found in other burrows, “says Liu.
“We’re always trying to find some evidence, and unfortunately the proposed samples don’t fill this gap,” O’Connor said. “It’s just part of the paleo game, part of science – constantly correcting. I’m happy when we don’t understand things, because it means there’s research to be done, it’s inspiring.”
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