Scientists are challenging the reported discovery of fossilised lice-like bugs crawling through dinosaur feathers, but the original researchers are standing by their interpretation. Y’all know what this means, right? Science fight!
In this corner, we have a team led by Taiping Gao from Capital Normal University in China. Back in 2019, this group claimed to have discovered a previously unknown louse-like insect, dubbed Mesophthirus engeli, found trapped in Burmese amber. A total of 10 specimens were found in two chunks of amber, all dating back some 100 million years ago to the mid-Cretaceous. Damaged dinosaur feathers were also detected within the amber fossils, prompting the scientists to declare it the oldest known example of dinosaur parasitism in the fossil record. Their resulting peer-reviewed paper was published in Nature Communications.
In the other corner, we have Isabelle Vea from the University of Illinois at Chicago and David Grimaldi from the American Museum of Natural History in New York. The duo says this interpretation is wrong, and that these insects couldn’t possibly be feather-feeding parasites. As Vea and Grimaldi point out in a Nature Communications Matters Arising letter published on Friday, the specimens are juvenile-stage scale insects, a group (specifically the Hemiptera order) of bugs that include bedbugs, cicadas, and aphids.
“When the original study was published, it garnered a lot of media attention and so when I saw the photo on one of these articles, I immediately recognised they were scale insect juveniles,” Vea, whose PhD dissertation was on fossil scale insects preserved in amber, explained in an email.
Grimaldi saw it the same way, prompting the biologists to conduct their own research and pen a response.
To that end, the team studied other scale insect juveniles (i.e. nymphs) found trapped in amber, while scanning the literature to find photos of living specimens. They also contacted Gao to gain access to the specimens, but because the fossils are located in China, the team was instead given high resolution images which “were enough to confirm our hypothesis,” said Vea.
The primary mistake made by the authors of the original paper has to do with how Gao and his colleagues described the mouthparts of the fossils, according to Vea and Grimaldi. Drawings made by the researchers are not “realistic,” said Vea, because the mouthparts of lice — the group they assigned the fossils to — are “not positioned ventrally [in front] as depicted in the drawing.”
To which she added: “Lice mouths are normally extending forward of the head. For example, if we position a lice mouth on a human head, it would be located on top of our head. The position of the mouthparts on the fossil is indeed ventrally, which is characteristic to the mouth location of a group of insects in the Hemiptera order, a different insect lineage,” explained Vea.
The teams on the new letter says Gao and his colleagues also misinterpreted the type of mouth on these insects as chewing mandibles, “but none of the specimens examined show clear chewing mandibles,” explained Vea. “A photo on their publication actually shows external mouthparts that contain a sucking stylet — similar to a straw — as found in scale insects.”
The original team also failed to address the absence of a head-thorax-abdomen division (lice juveniles have this division, but scale insect juveniles do not), and they interpreted claws seen on the legs of these insects as claws used for grasping onto feathers, which Vea believes is a mistake.
As for the damaged feathers, the team doesn’t believe that the bugs found trapped inside the amber fossils had anything to do with that. The feathers could’ve been damaged in any number of ways. There’s also no evidence that the insects were grasping onto the feathers, and their mouths were not designed for chewing, according to Vea and Grimaldi.
On that last point, the majority of scale insects, also known as coccoids (or coccoid crawlers, because they’re often found crawling on plants), have specialised mouths for sucking sap from plants.
While Vea and Grimaldi’s interpretation raises a number of substantive issues, the original research group is standing by their claims. Chung Kun Shih, a co-author of the original study and a scientist from the National Museum of Natural History at the Smithsonian Institution, said Vea and Grimaldi have it wrong.
“We do not agree with the positions and comments from Dr. Grimaldi and Dr. Vea that Mesophthirus engeli are nymphal stages of scale insects,” he explained in an email.
Shih and his colleagues sent a Reply Letter to Nature Communications to “address their concerns and comments based on our detailed observations and studies of our specimens in two pieces of amber” and to “highlight the significant morphological differences among our specimens and the nymphs of documented fossil scale insects.”
In this letter, the team “compared and listed details of differences in insect body [characteristics] among our specimens and the nymphs of documented fossil scale insects,” which they did by analysing specimens under the microscope and in photos. Vea and Grimaldi “drew their conclusions only based on the published photos without examining the specimens,” said Shih.
“We do appreciate different opinions and viewpoints by Dr. Grimaldi and Dr. Vea for academic debate and discussion,” added Shih. “But we are disappointed that our Reply Letter was not accepted for publication by the Editorial Office of Nature Communications.”
Nature Communications did not immediately respond to request for comment about why the Reply Letter was rejected, and whether or not the authors will be asked to retract their 2019 paper.
This debate about ancient bugs found trapped in amber may not sound like a big deal, but these things matter.
“Aside from being a sensational discovery, finding dinosaur feather-feeding lice would have had an impact on future studies of the evolution of lice,” explained Vea.
What’s more, Vea and Grimaldi wrote their response and submitted it nine days after the original paper was published “in the hope it would be reviewed quickly,” but the review process took more than a year, during which time “14 other published articles in scientific journals have cited this paper,” she said.
What happens next in this debate is unclear, but Shih said his team is continuing to do research in this area. Since the publication of their 2019 paper, these scientists have continued their investigation of feather-feeding lice in amber, and they “expect to get more findings and data to support and elucidate lice — or lice-like insects — feeding on feathers in the near future,” he said.
Indeed, if anything is going to settle this science fight it’s going to be more evidence. Science — and the scientific method — continues.