The smallest dinosaur in history

With regard to the “smallest dinosaur in history” incident that Chinese scholars have been arguing about, new progress has once again been made. On March 19th, according to researchers from the Institute of Paleontology and Paleoanthropology of the Chinese Academy of Sciences, they have submitted an English questioning article on the paper “Oculudentavis khaungraae is the smallest dinosaur in history” to a related journal Review and release on the pre-printed website bioRxiv- at the same time.

In addition, the authors of the questioning article stated that they had contacted the corresponding author of the “Kuanya Eye Tooth Bird” paper in the United States for the first time. The corresponding author said that they had considered negotiating with the editor of “Nature” to withdraw the manuscript. According to Caixin, Zou Jingmei, a foreign researcher at the Institute of Paleontology and Paleoanthropology of the Chinese Academy of Sciences, said that she has contacted the editor of Nature and will make an errata, but the editor of the journal believes that there is no need to retract the paper because after all, the scientific community often makes mistakes. Also, the reviewers who peer-reviewed the paper also thought it was a bird. “The previous mistakes will be corrected by the scientists. The process of scientific research is like this. We make hypotheses, find new data, and then make new hypotheses.” Wang Min, a researcher at the Institute of Paleontology and Paleontology of the Chinese Academy of Sciences, said that it is still unknown whether to withdraw the manuscript, and various factors need to be considered.

Latest evidence
According to Caixin reports, Zou Jingmei, one of the authors of the paper, believes that the doubters’ views cannot be conclusive evidence. For example, the questioner found that the bird had an anterior orbital hole, and the “eye-tooth bird” in the amber fossil did not have an anterior orbital hole, so it was considered that it was not a bird. However, Zou Jingmei believes that there are also cases where birds do not have an orbital foramen, so this question is not true. However, the English questioning article further pointed out that the author of the original paper reported the presence of lacrimal bones. As long as lacrimal bones are present in birds, the anterior orbital foramen cannot merge with the orbit and disappear. They determined from the cT scan data that the lacrimal bone does exist and is close to the maxilla, which means that the lacrimal bone of the “eye-tooth bird” is not in the state of the bird, and the anterior orbital foramen does not exist, which is consistent with the characteristics of lizards.

In this pre-printed English questioning article, in addition to reiterating many previous questions, such as the lack of anterior orbital foramen, lateral teeth, and phylogenetic analysis only in birds, after obtaining the original CT scan data of the original paper Added important new anatomical evidence that was never mentioned in the original paper, including confirmation of the absence of a square yoke bone, the presence of a pinhole associated with the pineal gland, and the presence of teeth on the ventral surface of the palatine and wing bones Columns and so on. The questioner stated that these important anatomical structures have never been found in dinosaurs and birds, but are very common in lizards, and further support that this specimen belongs to a certain lizard.

“Minimal Dinosaur” Event Review
On March 12, a study on “the smallest dinosaur in history” appeared on the cover of “Nature” magazine. The research paper was jointly completed by Xing Lida, associate professor of China University of Geosciences (Beijing), Zou Jingmei, a foreign researcher at the Institute of Paleontology and Paleoanthropology, Chinese Academy of Sciences, and LuisChiappe, dean of the Dinosaur Research Institute of the Natural History Museum in Los Angeles. The author found a dinosaur the size of a hummingbird (a broad sense of dinosaurs including birds) in a piece of amber with a history of 99 million years. The skull is intact and the length of the beak is only 7.1 mm. Since the morphological characteristics of this specimen are different from all other birds, the author of the thesis established a new genus and new species, and named it Kuanya Eye-toothed Bird.

bioRxiv is a free online archive and distribution service for unpublished preprints in life sciences. By publishing preprints on bioRxiv, authors can immediately provide their findings to the scientific community and receive feedback on drafts before submitting them to journals

According to the paper, the skull of “Kuanya Eye and Tooth Bird” in amber fossils is only about 14 mm long, and a huge eye socket is visible, with a diameter of about 4 mm. Although the size of Kuanya Eye and Tooth Bird is very small, its teeth are better than all other There are many ancient birds, with 18-23 teeth on each side of the upper jaw, 29-30 teeth on each side of the bone, and it has a sharp beak. Judging from the skull size of Kuanya’s eye-toothed bird, it is smaller than a hummingbird. It is the smallest ancient bird discovered to date and may represent the smallest Mesozoic dinosaur to date.

But just one day later, the paper was met by Wang Wei, Institute of Geology and Geophysics, Chinese Academy of Sciences, Li Zhiheng, Wang Min, Yi Hongyu, Lu Jing, Institute of Paleontology and Paleontology, Chinese Academy of Sciences, and Hu, University of New England, Australia Han and other colleagues questioned. They believe that “Kuanya Eye Tooth Bird” is not a bird, but more like a lizard. The questioner said that the space for assigning “Kuanya Eye Tooth Bird” to a bird or a dinosaur is extremely limited, and the shape of the “Kuanya Eye Tooth Bird” head shape is not unique to birds, and has a close relationship with birds / dinosaurs. Distant reptiles also have heads with long and pointed mouths, nostrils moving backwards, and big eyes, such as the shoveling lizard and the velociraptor among lizards. Therefore, based on the similarity of these continuous shapes, it cannot be concluded that the specimen belongs to birds / dinosaurs. Moreover, there is no anterior orbital hole on the skull of Kuanya Eye Tooth Bird, nor any trace left by the anterior orbital hole, and all lizards have no anterior orbital hole. According to this, the questioner believes that from the point of view of this specimen without an orbital hole, “Kuanya Eye Tooth Bird” is more like a lizard.

In addition to the anterior orbital hole, “with lateral teeth” and “without square yoke bones” is also the reason why the doubters believe that “Kuanya Eye Tooth Bird” is more like a lizard. According to the graphic description in the paper, the teeth of the maxillary bone of the “Kuanya Eye Tooth Bird” in amber obviously have the characteristics of lateral teeth, which is very common in lizards, but the teeth of all birds / dinosaurs are grown in the jaw. Grooved teeth in the alveolar bone. In the descriptions of scholars’ papers such as Xing Lida, “Kuanya Eye Tooth Bird” has no obvious characteristics of square yoke bones. The square yoke bone at the back of the orbit is an important difference between the lizard and the bird / dinosaur skull. In modern birds, the square yoke bone is healed together at the end of the yoke branch, while the lizard has no square yoke bone at all. At this point, “Kuanya Eye Tooth Bird” is also more like a lizard.

In addition, the scleral bone characteristic of lizards is very obvious in amber specimens. According to articles by scholars such as Wang Wei, although dinosaurs and birds also have scleral rings, the shape of each scleral bone is very simple. In the “Kuanya Eye Tooth Bird” skull in the paper, each scleral bone is narrowed in the middle, and the whole is scoop-shaped. This feature has only been found in lizards. Based on the above doubts, the doubters believe that “Kuanya Eye Tooth Bird” is not a bird, but more like a lizard.

The dispute continues?
One of the skeptics, Wang Min, a researcher at the Institute of Paleontology and Paleontology of the Chinese Academy of Sciences, said that many scholars in the field of biology are not lacking in colliding with the views of their counterparts in the industry, and they have raised their own doubts about the research methods and conclusions of a scholar The rebuttal is quite normal, they only pursue the truth of science. Faced with doubts, Xing Lida, the author of the paper and associate professor of China University of Geosciences (Beijing), said, “The new findings are controversial (normal), and we suggest that the other party publish discussions in academic journals.” In addition, Xing Lida also said on his personal Weibo, Academic issues have their own specifications. We recommend that scholars interested in participating in the discussion follow the academic process … Due to preservation factors, most fossil specimens have their own limitations …, and we look forward to progress in the discussion. ”

However, the questioner believes that, combined with the latest submitted review articles and the public information of the original paper, it can be seen that this specimen is well preserved in amber, and the bone structure is very clear, without much deformation. The cT scanning technology of the cooperative team is excellent, the scanning results are also very clear, and the analysis of morphological characteristics is not prone to deviation. Zou Jingmei said that the only evidence that this new species is not a bird comes from a new sample that provides data on the skull after the skull, but the research on the new sample has not been peer-reviewed and published, so for the time being It cannot be formally regarded as a “scientific basis” to support the species as a lizard rather than a bird.

At present, English questioning articles have been submitted to related magazines for peer review. Question whether the article can pass the peer review? What is the truth of the “minimal dinosaur event”? Let us look forward to the collision between the subsequent research of the two teams and academic views.