Reproductive frustration theory and evidence for the extinction of dinosaurs

At present, egg fossils of ancient reptiles, especially dinosaur egg fossils, have been discovered in many places around the world. According to the morphological structure, dinosaur eggs can be divided into short round eggs, oval eggs and long eggs. Dinosaur eggs vary greatly in size, with varying ranges in eggshell thickness and internal and external "ornaments", eggshell structure, and the proportion of vertebral and columnar layers in the shell. In order to conduct in-depth research on the internal characteristics of dinosaur eggs, scientists have used very new technologies and various methods, such as scanning electron microscopes, X-ray diffractometers, polarizing microscopes, CT scanners, etc. In recent years, Chinese scientists have used medical CT technology for the first time to conduct non-destructive research on the internal structural characteristics of dinosaur egg fossils unearthed in Laiyang, Shandong Province. They have discovered that some dinosaur egg fossils in Laiyang, Shandong Province have dinosaur embryos that cannot be observed by other methods.

Laiyang dinosaur eggs

The dinosaur egg fossil from Laiyang, Shandong Province is gray-black in color and oval in shape, with one end blunt and one end pointed. The maximum long diameter is 98 mm, the maximum transverse diameter is 70 mm, and the minimum transverse diameter is 60 mm. The surface of the eggshell is rough with a few cracks. During the excavation, a small amount of eggshells fell off, and a small amount of brown-red silty mudstone adhered to the surface of the eggshells. Eggshell thickness is 2-3 mm. Using the GE9800 medical whole-body CT scanner for transverse scanning, the outline and position of the egg shell, egg albumen and yolk can be clearly distinguished, and some very intact gastrula stage blastoderms can also be observed. The blastoderm is located on the more convex side of the egg, close to the edge of the egg white of the eggshell, and is about 80 mm long and 8 mm thick.

In-depth study of these dinosaur eggs has led researchers to believe that the extinction of dinosaurs is related to their reproductive frustration. The manifestation of reproductive frustration is that there are problems with the hatching of a large number of dinosaur eggs.

Based on the dinosaur eggs produced in the original layer, there is evidence that dinosaurs had the habit of ovulating in nests, ranging from a dozen to dozens of eggs. This high egg production rate is an ecological strategy that relies on quantity to ensure the normal number of hatchings and maintain the normal number of surviving cubs. It is called r-selection strategy in ecology.

As far as the genetic characteristics of dinosaurs themselves are concerned, the unity of the population must be taken into consideration. Large vegetarian dinosaurs mostly lived near water sources with lush vegetation, and their breeding grounds were never far from their living areas. Their large bodies and dependence on water bodies made it inconvenient for them to migrate long distances. Under relatively stable and favorable environmental conditions, , there is no need for them to migrate long distances. In this way, over time, the opportunities for hybridization of such dinosaur populations will inevitably be reduced, resulting in the purification of the population and the formation of many local genera and species. Evidence for this can be found from paleontological research. Purification of the population reduces egg hatchability to some extent. If a dinosaur is too young or too old when laying eggs, it is not conducive to the hatching of the eggs. The health of the body also affects the hatching rate.

As far as the dinosaur eggs themselves are concerned, being too heavy or too light is not conducive to hatching. Since the size of an egg is directly proportional to its weight, eggs that are too large or too small for the same dinosaur species will not be conducive to hatching. Therefore, the hatchability of eggs of the same species with a large range of size variation must be lower than that of eggs with a small range of size variation. As for short round eggs and long eggs, the size range of short round eggs is smaller than that of long eggs. From this point of view alone, the hatching rate of long eggs should be lower than that of short round eggs. Of course, dinosaurs that laid long eggs could make up for this shortcoming by increasing their egg production rate or improving their eggshell structure. However, whether it is a short round egg or a long egg, egg shape is another factor that affects the hatchability. Eggs that are too long or too round have a low hatchability. Judging from the dinosaur eggs in Laiyang, Shandong, it seems that the above problems have occurred more or less.

Eggshell thickness is another important factor affecting hatchability. The eggshell thickness of similar eggs generally has a certain range of variation. For example, the eggshell thickness of short round eggs is larger, about 2 mm. However, among the short round eggs discovered in Laiyang, the eggshells unearthed from the lower layer are thicker, while those from the upper layer are significantly thinner. The average eggshell thickness of long eggs is 0.9 to 2.0 mm, which is thinner than that of short round eggs. Egg shells that are too thin or too thick are not conducive to hatching. Existing data show that the phenomenon of dinosaur eggshells gradually thinning from bottom to top in the strata is not only seen in Laiyang, but also in other areas of my country and Europe. Some eggshells are less than 1 mm thin, especially thin-shelled eggs in the late Late Cretaceous. It is difficult to ensure normal hatching of such eggs. Therefore, it is certain that a large number of dinosaur eggs did not hatch by the time the dinosaurs became extinct in the late Cretaceous.

The internal quality of eggs also has an important impact on hatchability. Most reptiles are different from birds in reproduction. Parents cannot actively use their own body temperature to incubate eggs, but mainly rely on the heat energy provided by the sun. The incubation process is also affected by temperature. and environmental factors such as humidity. According to the burial conditions of dinosaur egg fossils in the original layer, after the dinosaur eggs were laid, the strata generally received continuous sedimentation without any traces of later stirring and transportation. Such signs indicate that the dinosaur eggs were likely to be like Like crocodiles and other reptiles, the eggs are covered with the surrounding sand to protect them from contamination or damage, and then they can only enter the incubation stage under the control of the environment. According to the observation of CT scans of dinosaur eggs in Laiyang, Shandong, it seems that the existence of air chambers is not visible. The presence and size of the air chambers can indicate the duration of egg laying. The fossilized eggs without air chambers indicate that the eggs stopped hatching and died soon after they were laid, and then entered the petrification stage of becoming fossils.

All the above phenomena indicate that dinosaurs in the late Late Cretaceous had serious problems with egg incubation, which caused the reproduction of dinosaurs to be frustrated. Researchers of these dinosaur eggs believe that this reproductive failure is likely to be the root cause of the extinction of dinosaurs.

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