Anti-lost, accessible by elevator
Safety Island newspaperman Liu Yadong A
Source: Global Science
Author: Global Sciences
A restoration of the long-armed mixed-edged dragon (Ambopteryx longibrachium) appeared on the cover of Nature (Image: Zhang Zongda)
Wang Min is committed to the study of the origin and early evolution of birds, and has named more than 30 genera of primitive birds, accounting for about 1/3 of the world's currently known Mesozoic bird species. Among his many research results, there is a class of dinosaurs that is particularly "strange" and also appeared on the cover of the 2019 nature magazine.
Written by | Twenty-seven
Review | Wang Min
For many paleontologists, "birds are descendants of dinosaurs" may not be new knowledge. Especially when we look at the entire Mesozoic Era, growing feathers and flying into the blue sky seems to be one of the "main tasks" of dinosaurs. However, in fact, the process of dinosaurs from dominating land to flying to the sky is much more complicated, for example, there was once a class of dinosaurs that made different flying attempts from birds, they are "good at climbing birds" dinosaurs.
The sudden appearance of "strange" dinosaurs
In the middle and late Jurassic Period, about 160 million years ago, there lived a strange group of dinosaurs, they were not large, but their limbs were slender, especially with extraordinarily long fingers, and seemed to have strong climbing ability, hence the name "Acropping Birds". These "strangely shaped" dinosaurs attracted the attention of paleontologists as soon as they appeared, but due to the limited number of fossils found and poor preservation, it is difficult for researchers to determine their relationship with other dinosaur taxa.
In 2015, Nature published a new ornithischian dinosaur, Yi qi, named after its "odd" body structure and the "wing" membrane structure preserved in fossils. But it did not belong to pterosaurs, but to a dinosaur – taxonomically, pterosaurs belonged to the order Pterodactyls, which were not a type of dinosaur (sauropods and ornithopods), but more like "sisters" of dinosaurs. In our general understanding, the biggest difference between pterosaurs and dinosaurs is whether they had membranous wings, but the odd pterosaur broke this boundary. It has three fingers at the ends of its forelimbs, of which the third finger is extremely elongated. From its wrist, a long rod-like bone protrudes, and when the fingers and rod-like bones are opened, they can support the wing membrane to form wings.
Rod-like bones (orange arrows) and membranous wings (blue arrows) appear "suddenly" in Chiptera (Credit: Xu, X., Zheng, X., Sullivan, C. et al, 2015)
The appearance of the pterodactyl does not answer the question about the evolutionary position of the climbing bird dragon, but makes the whole story more confusing. Because in other dinosaurs, no such membranous wing has ever been found, nor has there been a bone related to this rod-like long bone. Although the bones of vertebrates vary widely, it is rare to see a taxon "suddenly" grow a bone of this length. In addition, the preservation of the fossils of Pterosaurus is not intact, so after the discovery of Pterodactylosaurus, many scholars are skeptical about whether Pterodactyl really had membranous wings and rod-like long bones.
Gliding "Batman"
What ended the controversy was the publication of the long-armed hybrid dragon fossil four years later. The dragon was found in the Late Jurassic formation of the Yanliao biota and was about 32 cm long, the size of a pigeon. Its most obvious feature is that it also has membranous wings and long rod-like bones, which directly verifies the findings in Pterodactylosaurus. In addition, the long-armed hybrid dragon also had a tail bone similar to that of a primitive bird, which allowed its body center of gravity to move forward and remain stable during flight. Although the sternum is not well developed enough to provide enough muscle strength for flapping wings, the researchers speculate that the dinosaur was already able to glide skillfully through the air. The article was published in Nature in 2019 as a cover article, and the first author was Researcher Wang Min of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences.
"The specimen was accidentally discovered by a local fellow, and only part of the hind limbs and skull were exposed." Wang Min described, "When my fellow villagers contacted us, they only thought it would be a feathered dinosaur, nothing special. Later, the more it was repaired, the more different it became, especially when the rod-shaped long bones were repaired, everyone felt particularly surprised. ”
Fossils of long-armed hybrids (left) and line drawing (right), the brown area in the right is feathers, the dark gray area is membranous wing, the blue area is possible gastric capacity, and the se is rod-like long bone (Image source: Wang, M., O'Connor, J.K., Xu, X. et al., 2015)
With the discovery of the long-armed hybrid, the position of the climbing bird dragon on the dinosaur family tree has become clearer. "The skeleton fossils of this long-armed hybrid dragon are very well preserved, with forelimbs and hind limbs preserved, so we conducted a phylogenetic analysis of these paraornithosaurus dinosaurs that are relatively close to birds." Wang Min said. At first , because of the obviously flight-friendly characteristics of the climbing birds , some scholars suspected that they may have been the direct ancestors of birds or were very closely related to birds. However, the results of the study show that the climbing birds are more like a dinosaur that "went wrong" in the process of flying.
"If you look at it from a large time frame, the evolution of dinosaurs to birds was accompanied by the evolution of flight ability: the entire main line of evolution was to lengthen the forelimbs, shorten the tail vertebrae to the tail bones, and move the body's center of gravity forward - it can be said that everything is for flight." Wang Min pointed out that for the climbing birds, a similar trend was also shown - their forelimbs were particularly long: "Among these dinosaurs that are closely related to birds, their forelimbs are almost the longest... This is a clear trend, a need to adapt to flight. ”
Long-armed hybrids related to other dinosaurs (Credits: Wang, M., O'Connor, J.K., Xu, X. et al., 2015)
However, there is a key difference between the body structure of the adversary and birds. Although the forelimbs tend to elongate, the trespassers extend their forelimbs through humerus, ulnar bone, and phalanges, corresponding to our arms and fingers, while in groups more closely related to birds, the forelimbs are elongated by the extension of the metacarpal bone, because their "palms" require a large number of flight feathers attached. The "membranous wings and short metacarpals" of the "membranous wings and short metacarpals" of the birds and the "feathered wings and long metacarpal bones" of birds reflect significantly different flight patterns and evolutionary paths.
Unfortunately, this "maverick" dinosaur did not survive. At present, fossils of climbing birds have only been found in the middle and late Jurassic strata, and researchers suspect that they may have become extinct before the Cretaceous. As for why their existence is so short, Wang Min and the research team have also had some conjectures: "Another type of animal with membranous wings that contemporaneously with it (apatent bird-climbing dragons) is pterosaurs, which have a strong flight ability and are widely distributed." At that time, some mammals with gliding ability were also found, and some paraorphobic dinosaurs that were very close to birds also grew wings on their forelimbs. Therefore, the competition faced by the dragons who are good at climbing birds is relatively diverse. After all, they are so small, to face the competition of the above three, it is likely that the competitive advantage is not so strong. ”
What are birds?
Although the "heavenly plan" of climbing birds and dragons failed, we all know that another dinosaur evolved into birds soaring in the sky and becoming one of the most diverse vertebrates. Wang Min's work focuses on the evolution of these birds from dinosaurs in the long history of nearly 150 million years. Although the core work is the evolution of Mesozoic birds, Wang Min especially hopes to make some new theoretical and methodological attempts to better use the information revealed by fossils to analyze the evolution patterns of birds.
It's not easy to sort out the intricate evolutionary paths of birds, especially for paleontologists, whose work is more like "peeping leopards in the tube"—digging up traces of evolution from the remaining fossils. This requires not only meticulous and rigorous indoor and outdoor work, but also the courage to make assumptions and judgments, and the courage to explore the unknown world. Wang Min hopes to dig more and use the information provided by fossils, "In fact, fossils give us a very rich information, but he will appear more and more complicated, and it is easy for us to drown in this information." So I hope to distill this data and see if there are some clearer and more intuitive ways to help us understand the dynamic path of bird evolution. ”
For Wang Min, the ultimate goal of the study is to answer a seemingly simple question — what are birds: "This question is my own thought, and others often ask, 'You have been working for so long, have you not yet answered such a simple question?'" I'll say there really isn't. "The simpler the question, the harder it is to answer. Wang Min hopes to summarize a sentence in the future, very succinctly telling everyone the explanation and definition of birds, "It is difficult to find a distinctive feature that belongs only to birds and does not belong to other animals." For example, some of our previous introductions to birds are winged and active flight, but we found that these characteristic dinosaurs also have. The line between dinosaurs and birds has become very blurred, so I've been thinking about how to tell this thing in more concise terms. ”
Researcher Wang Min
Thesis Link:
https://www.nature.com/articles/nature14423#citeas
https://www.nature.com/articles/s41586-019-1137-z/figures/3