Some paleontologists believe they have found fossilized dinosaur DNA. Others are not so sure


Dinosaur researchers working on extremely well-preserved remains from Jehol Biota in northeast China recently reported that they had detected fossilized biomolecules in a duck-billed dinosaur from the Late Cretaceous Period.

The intriguing microscopic material was found in the femur of a Caudipteryx, a feathered turkey-like dinosaur that lived around 125 million to 113 million years ago. The team scanned the femur cartilage and stained it with chemicals called hematoxylin and eosin, which are used to highlight cell nuclei and cytoplasm in modern cells.

They also stained the cartilage of a chicken and found that dinosaur and chicken cartilage lighted in the same way. Researchers say nuclei and chromatin, the material our chromosomes are made of, were visible. The team’s research was published last week in the journal Nature Communications Biology.

“Geological data has accumulated over the years and has shown that the preservation of fossils in the Jehol Biota is exceptional due to the fine volcanic ash which buried the carcasses and preserved them down to the cellular level,” said the study co-author Li Zhiheng, a vertebrate paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, in an Academy press release.

Members of this research team also described the discovery of genetic material in another specimen last year; As Gizmodo reported at the time, some scientists were also skeptical of their claims that traces of genetic material were preserved in the fossilized skull of Hypacrosaurus. The Caudipteryx fossil in the new work is about 50 million years older than the Hypacrosaurus.

“They were identified using completely different methods than the Hypacrosaurus,” wrote Alida Bailleul, lead author of the new article, in an email to Gizmodo. “But what was striking was the hematoxylin staining of the Caudipteryx cell nucleus – it was comparable to the staining seen in a chicken cell nucleus,” said Bailleul, a paleobiologist at the Institute of Paleontology and Paleoanthropology of Vertebrates in Beijing.

If this fossil revealed the same structures as seen in modern chicken, it would be a remarkable demonstration of the ability to conserve biological material and the mercy with which cartilage has been treated by Earth’s often destructive processes. But not everyone is so convinced of what exactly appeared in the spots.

“I don’t really see how much that has changed here,” said Evan Saitta, a researcher at the Center for Integrative Research at the Field Museum of Natural History in Chicago. “The change in weather that interests us here is not between the hypacrosaur and this new specimen; the difference is the amount of time between DNA preservation well taken care of and any of these fossils.

The oldest sequenced DNA was described in an article in February and emerged from the teeth of a woolly mammoth about 1 million years old. All dinosaurs (except birds) became extinct around 65 million years ago. This makes the materials of the dinosaurs “absurdly older” than the “spectacular” results of the woolly mammoth remains, Saitta said.

So what exactly reacted to the dyes and stains the recent team applied to dinosaur cartilage? According to Saitta, it could be microbes settling in dinosaur remains or a mineral filling of the space freed by deteriorated genetic material. The latter is the opinion of Nic Rawlence, the director of the paleogenetics laboratory at the University of Otago in New Zealand.

“The current limit for ancient DNA is 1.2 million years ago, and we don’t expect to be able to go much further back in time, certainly not to the age of dinosaurs,” Rawlence said. in an email to Gizmodo. “Although these fossilized cells and the DNA of this new dinosaur may look like that of a modern chicken, it is a stone copy, where cells and DNA have been replaced by minerals, the same way that a dinosaur bone is a mineralized version of modern bone. BONE.”

When bones fossilize, they do so from obvious macroscopic features to the smallest parts of their structure. This allows paleontologists to do things like learn about the growth rates of T. rex, for example, when holes appear in the bone where the blood vessels were located. But genetic material is deteriorating rapidly – one team estimated that DNA would cease to be readable after 1.5 million years, causing mammoth tooth to find itself bustling near the upper limit of material. And the mammoth remains were only so well preserved thanks to their embedding in the permafrost.

“Chemically, you’re dealing with a completely different setup of compounds here, compared to when you look at permafrost which is roughly comparable to frozen turkey in your freezer, to some extent,” Jasmina said. Wiemann, molecular paleobiologist at Yale. University, in a video call.

This makes the situation of this million-year-old mammoth fundamentally different from that of the 125-million-year-old Caudipteryx. Although mammoth teeth underwent diagenesis – the process by which organic compounds are gradually replaced by inorganic elements like minerals – they have been cooled by the Siberian climate, preserving biomolecules to this day. (This is also the reason why you sometimes read that Ice Age researchers can eat what they studied, like the steppe bison.)

A woolly mammoth skeleton.  The oldest sequenced DNA comes from the teeth of a 1.2 million year old mammoth.  (Photo: PHILIP FONG / AFP, Getty Images) A woolly mammoth skeleton. The oldest sequenced DNA comes from the teeth of a 1.2 million year old mammoth. (Photo: PHILIP FONG / AFP, Getty Images)

“When it comes to actual DNA molecules, I think it’s next to impossible for such molecules to stay in dinosaur material,” wrote Love Dalén, a paleogeneticist at the Center for Palaeogenetics who was part of the team at the mammoth tooth, in an email to Gizmodo. “We know from both massive empirical studies and theoretical models that even under completely frozen conditions, DNA molecules will not survive more than about 3 million years.”

“Just because different dyes or stains react with parts of a fossilized remnant does not mean that actual DNA molecules remain in the fossil,” Dalén added.

Plus, just because a bone fossils does not mean that every component of the once-living creature is swapped, tit for tat, for a specific mineral or metal compound. Every dead dinosaur in every deposit in the world means that a unique set of conditions are met, so no two fossils are really chemically identical. This means that a Montana Hypacrosaur bone will have undergone a different type of fossilization than that of a Caudipteryx in China, making the job of molecular biologists, geochemists and paleontologists much more complicated.

“It passes, like, a grinder, but what comes out of it ends up being very similar,” Wiemann said. “We lack a fundamental understanding of how fossilization works. I think that’s the whole challenge here.

Mammoth DNA could be sequenced because it was more frozen than fossilized. That is, the DNA has not had the opportunity to interact with the molecular environment around it, and in particular with water, which causes the DNA to break down, such as A gigantic article co-author told Gizmodo.

So besides the question of what exactly was preserved in the Caudipteryx, it’s important to recognize that dinosaur DNA cannot be sequenced, at least not yet. The molecules have just gone through so many changes that they don’t look like the animals they were a part of. But ancient biomolecules may linger: Dinosaur proteins have apparently been found in bones that are 200 million years old, although, as a research team including Saitta pointed out in an article, the bones of dinosaurs in decomposition are a happy home for microbes, which can grow into genetic dinosaurs. Equipment.

Part of the problem with the recent article, several scientists said, was the staining method used to compare Caudipteryx and chicken nuclei. Hematoxylin and eosin can bind to all kinds of things, not just genetic material, the researchers said, making the results pretty general. “I think it’s difficult to apply a staining protocol that isn’t at all very specific to something like fossil materials that we don’t even understand what they actually represent,” Wiemann said.

A useful step in resolving such ambiguity would be to cross-stain the staining results with additional independent methods of cartilage examination. Such “triangulation” would help solve the tissue problem, Saitta said. Wiemann suggested using mass spectroscopy to examine the whole bone and see if the colored material could be mapped to nucleic acid bases or the sugar-phosphate backbone of DNA. It’s an “incredibly exciting line of research,” Wiemann added, saying these additional methods would help determine exactly what is preserved in the fossil.

“I firmly believe that if you are going into deep-time biomolecular, you MUST incorporate as many methods as possible, AND you must consider and exclude, with data, any alternatives, such as invasion by microbes, ancient or modern, ”Mary Schweitzer, molecular paleontologist at North Carolina State University and the Museum of the Rockies in Montana, told Gizmodo in an email. Schweitzer co-wrote the article on the hypacrosaur alongside Bailleul, who worked in Schweitzer’s lab. “For me, the ultimate goal is to get sequence information, so anything we can learn about the diagenetic alterations of these recovered molecules becomes critical.”

Two fossils, 50 million years apart, reveal a biomolecular dilemma within two years. If this timeline is to continue, more data could soon arrive, hopefully bringing more clarity to this exciting new area of ​​paleontology.

Source link

Leave A Reply

Your email address will not be published.