"Man" talk about the evolutionary history of dinosaurs - the miniaturization story of Alvarez's dragons. Ye Zi painting, courtesy of the Institute of Ancient Spine, Chinese Academy of Sciences
The Cretaceous period can be described as the "age of the dragon". During this period, the competition between dinosaurs became increasingly fierce, and a considerable number of theropod dinosaurs embarked on the evolutionary path of large-scale and even mega-scale. However, scientists recently discovered that among these behemoths, there was a mysterious class of dinosaurs, the Alvarez dragons, which had shrunk sharply in size in a relatively short period of time. This change may be related to the transformation of their "diet" from small animals such as lizards to social insects such as termites. The relevant research results have recently been published in the internationally renowned journal Contemporary Biology.
Xu Xing, a researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, introduced that the Alvarez dragons are a small theropod dinosaur and are distant relatives of the birds we are familiar with. They are slender, with slender legs and a pair of "small short hands". Fossils of such dinosaurs are found in Asia, Europe, and North and South America, and the fossil record extends from the Late Jurassic period, about 160 million years ago, to the end of the Cretaceous period, after which it became extinct along with most non-avian dinosaurs.
Ecological restoration maps of four representative Alvarezosaurs show differences in the size and feeding habits of Alvarezosaurus dinosaurs at different evolutionary stages. Han Zhixin, courtesy of the Institute of Ancient Spine, Chinese Academy of Sciences
The study found that the miniaturization of Alvarez dragons did not occur slowly and gradually, but in a short period of time, a sharp loss of body weight, a process that occurred mainly between 110 million and 85 million years ago. "The early Alvarezosaurus was also small compared to Tyrannosaurus rex and the like, weighing about 5 kg to 50 kg, which is the size of a turkey to a small ostrich. After miniaturization, the weight changes to about 0.5 kg to 5 kg, most of which are smaller than chickens and even about the same size as pigeons. Qin Zichuan, the first author of the paper and a doctoral student at the University of Bristol in the United Kingdom, said.
Why did Alvarezians have such "reverse growth"? The study found that the miniaturization of Alvarezosaurus coincided with the Cretaceous terrestrial revolution, a major environmental event that completely changed terrestrial ecosystems.
According to reports, at that time, flowering plants began to occupy the land, and the ecological environment underwent great changes. With the flourishing of flowering plants, social insects such as termites, ants, and bees bees began to flourish. At the same time, Alvarezosaurus began their miniaturization process. This temporal coincidence suggests that the miniaturization process of Alvarezosaurus may be related to their transition from carnivorous or omnivorous to insect-eating.
"It is generally believed that small theropod dinosaurs are opportunists and should not let go of food. Some early Alvarez dragons probably ate small animals such as lizards. Qin Zichuan said, "The late small Alvarez dragons are somewhat similar to today's small anteaters. They may have used their stout forelimbs to dig up and destroy termites such as decaying wood and mud nests before eating termites. Their teeth do not develop on the anterior side of their snout, which may leave a protruding channel for the longer tongue to stick to the anteaters. ”
A small alvarezosaur with only one finger found in China at the end of the Cretaceous period was a single fingered river-clawed dragon. Photo courtesy of the Institute of Ancient Spine, Chinese Academy of Sciences
As for why this transition occurred in Alvarez dragons, the researchers speculate that high-intensity ecological competition may be a reason, because during the same time, many of the distant relatives of Alvarez dragons are gradually enlarging, and some have gained weight by two to three orders of magnitude. By the end of the Cretaceous period, the niches of large carnivores should have been "overcrowded", and the "reverse growth" of Alvarezosaurus had won some space for survival.
However, the researchers say more evidence from functional and ecological studies is needed to concretely prove the Alvarez dragon ant-eating hypothesis. The study was done in collaboration with the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, the University of Bristol in the United Kingdom, George Washington University in the United States, and the University of the Witwatersrand in South Africa.
Planning: Gemdale
Text: Gemdale, ThunderCloud
Editor: Jiang Guocheng