Jimu news reporter Xiao Yang
Correspondent Ma Yucong
The Jimu News reporter learned from China University of Geosciences (Wuhan) that The university's Han Fenglu team accidentally obtained an egg fossil during a field expedition in Henan. After research, it has been confirmed that this is an embryonic fossil of a turtle about 100 million years old, which is the egg laid by an extinct type of giant Nanxiong turtle (Nanyang Yu turtle). In addition, the research team also explored the evolution of the breeding strategy of large turtles, and the related article was published online on August 18 in the internationally renowned biological journal "Proceedings of the Royal Society B: Biological Sciences".
(a) turtle embryonic egg fossil CUGW EH051 photo; (b) egg fossil partial enlargement, white arrows indicating exposed embryonic bones; (c) incubated Nanyang Yu turtle (imaginary) ;(d) fossil CUIG EH051 produced formation:
Turtles originated in the late Triassic period and have been on Earth for more than 200 million years. A large number of turtle and tortoise skeletons and egg fossils have been preserved around the world, but few turtle embryo fossils have been found. This is the first detailed study of the fossilized Cretaceous turtle embryo in Henan by the paleontological community, and it is also a rare new discovery that the turtle egg is associated with a specific adult genus species based on the embryo.
How do I confirm which turtle laid the egg? Han Fenglu's team, together with researchers from Canada and researchers from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, conducted a systematic study of the fossils. According to reports, the thickness of the eggshell of this fossil is nearly 2 mm, using the function relationship between the adult turtle and the egg in size and weight, the researchers inferred that the adult turtle body length of this embryonic fossil should be 1.6 meters, and finally classified into the Nanyang Yu turtle of the Nanxiong turtle family according to the body size, skeletal characteristics and origin and strata.
According to Ke Yuzheng, the first author of the article and a 2020 master's student in the School of Earth Sciences, the study involves the skeletal morphology, ecology, physiology, etc. of turtles, which requires a wide range of knowledge and accurate analysis capabilities, "Previously, we could find a lot of turtle fossils in the strata, and at the same time we could find a lot of turtle egg fossils." But, more often than not, we don't know who gave birth to these turtle eggs. Through information such as the morphology of the embryonic bones, we can correctly identify the relatives of these eggs, that is, which turtles give birth to these eggs. ”
According to reports, the study lasted two years. Initially, in order to maximize the access to embryonic bone information while reducing damage to the fossils, the researchers used microCT to scan the egg fossils as a whole and used 3D reconstruction to model the embryonic bones inside in three dimensions. From the CT image, it can be seen that the fossil bones of the egg are not related, and the slender bones have brought great difficulties to the overall reconstruction, so the researchers spent a full year to have a more accurate reconstruction of the internal bone morphology. "I would study the images repeatedly every day until one day I saw a pair of jaws that had just been repaired and became convinced that they were turtle embryos." Associate Professor Han Fenglu said. Subsequent research was carried out through three-dimensional models, etc., which lasted for another year.
Restoration and reconstruction of embryonic bones; the left figure is the 3D reconstruction map, and the red part of the right picture is the identified turtle embryonic bone
Ke Yuzheng introduced that when he was a senior in college, he studied in the field of ancient embryos under the guidance of Professor Han, but the research of embryonic fossils is very difficult, and the influence of ontology on bone morphology requires meticulous identification and reasoning. He first reconstructed the embryos further and further compared them with the stained specimens of the living turtle embryos, and then sliced and microscopically observed the eggshell fossils with the help of his brother Wu Rui. In addition to the study of the embryos themselves, he also carried out statistics and discussions on the reproductive strategies of turtles, and concluded that the reproductive strategies of large turtles generally showed the law of reducing the size of eggs, thinning of egg shells, and increasing the number of eggs.
Why does this 100 million-year-old turtle egg have an extremely thick eggshell? What was the living environment of the turtle at that time? For these questions, researchers have proposed a variety of hypotheses. In the end, it is believed that this thick eggshell is likely to be an adaptation to an abnormal extreme environment, but the specific influencing factors need to be further confirmed, and the geo-university team will conduct in-depth research on this.
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