Pictured above: Illustration of a Cretaceous land turtle (Southern Male Turtle) hatching from a tennis-sized egg.
About 90 million years ago, in what is now the middle of our country, a giant tortoise laid a nest of eggs the size of a tennis ball, with very thick shells. There is an egg that never hatched, and it has not been disturbed for tens of millions of years, preserving the fragile bones of the turtle embryo.
As shown in the image above: What kind of illustration a turtle egg might look like after hatching.
In 2018, a farmer found the turtle egg and donated it to a university. Now, scientists have conducted a new analysis of the egg and its rare embryos, marking the first time they have been able to determine the species of dinosaur-era land turtle embryos.
This specimen also explains why its species, the Southern Male Tortoise, went extinct 66 million years ago at the end of the Cretaceous Period, when the asteroid of the extinct dinosaurs hit Earth.
Thick eggshells allow water to penetrate, so in the late Cretaceous period, flocks of eggs may have been buried in nests in moist soil deep underground to prevent them from drying out in the arid environment of central China.
As shown in the image above: what kind of illustrations the nanxiong turtle pups may look like from different perspectives.
Darla Zelenitsky, associate professor of paleontology at the University of Calgary, Canada, said: "While these land turtles' unique terrestrial lifestyles, thick eggs and underground nesting strategies may have served them well during the Cretaceous period, these particular southern male turtles may not be able to adapt to the colder climate and environmental changes after the mass extinction at the end of the Cretaceous period." ”
As shown in the image above: Dara Zelenitsky, associate professor of paleontology, conducted the study with a 3D printed model of a Nanxiong turtle egg.
<h1 class="pgc-h-arrow-right" data-track="6" > the discovery of ancient turtle eggs</h1>
As shown in the image above: The size of the fossil egg is 5.4 × 5.9 cm.
According to Zelenitsky, the farmer discovered the turtle egg from the dinosaur era in Henan Province. Over the past 30 years, thousands of dinosaur eggs have been found in Henan Province, making the area famous. But compared to dinosaur eggs, she said, turtle eggs, especially those that preserve embryos, rarely turn into fossils because they are too small and fragile.
The nearly spherical turtle egg is 5.4 × 5.9 centimeters in size, a little smaller than a tennis ball. This is larger than most extant turtle eggs, only a little smaller than the eggs of galapagos turtles.
As shown in the image above: CT image of the embryonic skeleton hidden in the egg of the Southern Male Turtle.
The thickness of the eggshell is 1.8 mm. From this point of view, it is 4 times thicker than the eggshell of a Galapagos turtle and 6 times thicker than an egg with an average thickness of 0.3 mm. Larger eggs tend to be thicker, such as 2 mm thick ostrich eggs, but this egg is much smaller than an ostrich egg, with an average length of about 15 cm.
The researchers found that an equation that used the size of the egg to predict the length of the carapace showed that the thick egg was most likely born from a turtle whose carapace was 1.6 meters long. This measurement does not include the length of the neck or head, so the mother turtle is easily as long as a human.
As shown in the image above: Other turtle nests in this family contain 30 to 15 eggs.
<h1 class="pgc-h-arrow-right" data-track="27" > destined egg</h1>
The researchers used micro-CT scans to create virtual 3D images of eggs and embryos. The researchers found that by comparing these images to extant distant turtle species, the embryo appeared to develop nearly 85 percent.
Zelenitsky noted that part of the eggshell was broken, so it may have tried to hatch, but failed. Apparently, this is not the only embryonic turtle that has died prematurely.
The researchers said two thick-shelled egg fossils previously found in Henan Province, dating back to the Cretaceous Period, one with 30 eggs and the other with 15 eggs, are likely to also belong to the now-extinct Southern Male Turtle Family.
As shown in the image above: The now extinct southern male turtle family lives in Asia and North America. This is a fossil of a Southern Male turtle found in Alberta, Canada.
Zelenitsky said: "The turtles of this family are relatives of today's river turtles, they are very flat and evolved to live entirely on land, which was unique at the time.
Walter Joyce, professor of paleontology at the University of Fribourg in Switzerland, said: "The peculiarity of this newly discovered turtle egg study is that it performs a virtual 3D analysis of embryos, which helps to diagnose their species. ”
As shown in the figure above: fossil carapace of the Southern Male Turtle family found in China.
In addition, the study provides evidence that the Southern Male Turtle adapted to the harsh terrestrial environment and laid large, thick-shelled eggs in nests in moist soil.