2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
nest and clutch of therizinosaurus, a theropod dinosaur that lived at the end of the Cretaceous.
It seems that not birds, but also theropod dinosaurs began to take care of egg laying, and this began at least 80 million years ago. This is the conclusion reached by paleontologists who found fossils of 15 clutches of eggs, according to Geology, as well as in an editorial in Nature. The percentage of hatched chicks, which scientists estimated from shell fragments, was quite high - about 60 percent. This percentage is observed in modern crocodiles or birds that take care of the clutch and protect it from predators.
Communal nesting is typical for some modern birds, usually of the same species. In this case, the birds arrange nests close to each other. For example, colonies of public weavers (Philetairus socius) can nest up to 400 pairs of birds. This makes it easier for them to look after the nests, and in case of danger the birds can raise the alarm and warn the neighbors. The fact that some species of dinosaurs had communal nesting was known earlier. So, fossils of joint clutches of dinosaurs were found by paleontologists in Mongolia, in the Late Cretaceous Javkhlant formation. Some reptiles appear to have returned to their nesting sites over the years.
Recently, paleontologists have obtained circumstantial evidence that dinosaurs, like modern birds or crocodiles, protected their nests. Darla Zelenitsky of the University of Calgary and colleagues from four countries have found fossils of at least 15 nests and more than 50 eggs in the Javklant Formation. Scientists have dated them 80 million years ago. Some of the cubs have already hatched and fragments of the shell have been preserved from their eggs. The clutches were made in one season, as evidenced by a thin layer of sedimentary rock that was common to all 15 clutches. Some of the sediment got into the broken eggshells and filled them. The researchers suggested that the nests died when a nearby river flooded. Judging by the fact that some of the eggs were not broken, the flood was small.
Based on the internal and external texture of the eggs and the thickness of the shell, scientists suggested that the nests were made by theropod dinosaurs - a large group of reptiles, which included tyrannosaurs, ceratopsians and oviraptors. By the number of shell fragments, scientists estimated the percentage of hatched cubs. It turned out to be quite high - about 60 percent. About the same number of young birds and crocodiles appear in modern birds, which take care of the nests and drive away predators from them. The authors suggested that it is likely that the theropods who arranged the clutches also took care of them. If this is true, then the defensive behavior first appeared in feathered dinosaurs, and allowed them to increase the offspring's chances of survival.
Perhaps theropods did take care of their nests, agrees UCLA paleontologist Daniel Barta, who was not involved in the study. But it should be borne in mind that eggs broken by predators look very similar to those from which the cubs hatched.
The found clutches, apparently, belonged to not very large dinosaurs, the diameter of the eggs in them reached 10-15 centimeters (for comparison, the diameter of ostrich eggs is 12-15 centimeters), and apparently they incubated them. And recently, paleontologists found a nest of large dinosaurs and, based on its structure, suggested how large dinosaurs warmed the clutch without breaking or crushing eggs. They probably laid eggs along the perimeter of a large nest, while they themselves sat in the center and warmed them with their sides or limbs.
