Resolving an evolutionary dispute over the diet of small bird-like dinosaurs, Chinese paleontologists have found compelling evidence of their food preferences. A series of spectral analyzes helped reveal convincing traces of predation in the guts of furry lizards. New data helps objectively assess the diet of ancient animals, not just based on the structure of their peculiar limbs.

Six years ago, paleontologists in northwestern China discovered the remains of two previously unknown dinosaurs belonging to the family. alvarezsauridae. Alvarezsaurids are feathered theropods that were once considered primitive birds. These are small dinosaurs that lived on earth from the end of the Jurassic to the end of the Cretaceous period, rarely growing up to two meters in length. The Chinese find bridged the evolutionary gap between early and late forms of Alvarezosaurus.

The fact is that the front legs of the Upper Cretaceous species of this family are noticeably shortened. Linhenik (LinhenykusThe creature, which lived about 80 million years ago, had only one finger and claws. Their bodies also became smaller, and this metamorphosis was explained by a change in food preferences: alvarezsaurids began to eat insects instead of the meat of other animals. Indeed, the clawed, three-fingered paws of theropods are better suited for predators, and who can catch and hold with short limbs that are probably better suited for digging?

However, the hypothesis of a shift to insectivory remained a hypothesis in the absence of direct confirmation. Eating habits cannot be explained solely based on changes in the body structure of these theropods. But in a new study, Chinese paleontologists (including two experts who found the missing evolutionary links in 2018) talked about the contents of the guts of an Early Cretaceous Alvarezosaurus. The results provide the first visual evidence of their actual diet. The preprint of the article has been published on the website. bioRxiv.org.

Researchers examined specimens of three Alvarezsaurids: Jurassic Haplocheirus sollers about 160 million years old, Late Minor Shuvuuia desert And Bannykus wulantensisIt occupies an intermediate position. Among the ruins of the latter, parts of the digestive system are preserved – intestines with possible food residues. Since the material has been mineralized for a long time, to check what belongs to the lizard and what belongs to geological deposits, experts examined the composition of the particles using energy dispersive X-ray spectroscopy and electron probe microanalysis.

Paleontologists examined pieces of hard tissue through a scanning electron microscope. Among soft tissue remains, this has become the most convincing trace of ancient food. Another stage – Raman spectroscopy – helped reveal signatures unique to the bones and flesh of the prey. Chitin and plant remains were not found: This is the result of the last meal B. wulantensis He was not a vegetarian at all.

Scant data on the jaw structure of this lizard suggested similar preferences to later species such as auhuiya (hypothetical insectivores). But new results confirm that significant amounts of calcium phosphate are deposited in the intestine. B. wulantensis It is typical for bones and teeth. The same material is often found in the digestive tract and coprolites of carnivorous dinosaurs, as they were chewed with difficulty and swallowed in pieces.

However, scientists cannot rule out the possibility of an insectivorous diet of intermediate forms of alvaresaurids. The shift to such feeding habits remains potential, and if it did occur, according to paleontologists, it occurred during the later stages of evolution of bird-like theropods and coincided with body shrinkage. Length B. wulantensisAccording to comparative anatomy, it reached one meter in length and weighed up to 24 kilograms.