Dinosaur embryo with nasal horn

Embryo fossil

Exposed head of the sauropod embryo (Image: Kundrat et al. / Current Biology)

Sauropods – long-necked herbivorous dinosaurs – were the largest land animals to ever live on earth. An exceptionally well-preserved embryo of a Titanosaurus has now given researchers astonishing insights into the life and early development of the giant herbivores. According to this, the young animals could see three-dimensionally and had a kind of horn on their snout with which they could free themselves from their egg – similar to today’s birds and crocodiles.

When the first sauropod eggs were discovered around 25 years ago in Auca Mahuero, Argentina, in Patagonia, it was a sensation: For the first time, researchers were able to examine the embryos of dinosaurs and thus get an initial idea of ​​how the primeval giants developed from an early age. To date, embryology is one of the least explored topics around dinosaurs. Thanks to an exceptionally well-preserved find from Patagonia and new imaging technologies, researchers have now gained astonishing new knowledge. “The specimen we examined is the first almost completely preserved skull of a sauropod,” reports Martin Kundrat from the PaleoBioImaging Lab at Pavol Jozef Šafárik University in Slovakia.

Reconstruction of the embryo

With the help of a new imaging technique, synchrotron microtomography, Kundrat’s team succeeded in reconstructing what the sauropod’s skull probably looked like before hatching. After carefully removing the surrounding egg with acid, they were able to visualize anatomical structures of the embryo, including bones, teeth and tissues. The embryo skull, which is only about one centimeter in size, has shown unusual features. While the eyes of adult sauropods tend to be aligned laterally, in the embryo they point further forward and could have made three-dimensional vision possible. From the point of view of the researchers, this may allow conclusions to be drawn about the way of life of very young sauropods. While the adult sauropods with their laterally aligned eyes had a larger field of vision, which was useful for detecting predators, for example, the young animals could have benefited from spatial perception.

In contrast to the previously examined dinosaur embryos, the skull of the young Titanosaurus is not ossified, but the front part of the face is. Since hardly anything is known about the development time of dinosaurs in the egg, the researchers cannot use this finding to make any statements about how old the dinosaur embryo was. However, they suspect that the late closure of the skullcap in the Titanosaurus embryo is related to the development of important brain structures. The fossil also provides clues as to how the sauropod hatched from its egg: Until now, experts have assumed that young sauropods had a bony egg tooth, as is found today in lizards and snakes. Kundrat and his colleagues, however, discover a horn-like thickening on the embryo’s snout that may have helped break through the egg shell. This method would be more similar to that used by birds and crocodiles today. In the further course of life, the thickening presumably regresses, because it was not found in adult specimens.

Time capsules from the past

Presumably, the young animals of the sauropods differed in head shape and way of life from the adults and underwent significant changes in the course of their individual development. “Since our specimen differs in face shape and size from the sauropod embryos from Auca Mahuero, we cannot rule out that it is a new species of Titanosaurus,” says Kundrat. Like the well-known finds from Auca Mahuero, the egg in which the embryo was now located comes from Patagonia in Argentina. The shell, however, is thicker than that of the Auca Mahuero eggs and has a slightly different geochemical signature. As the egg was illegally exported from Argentina and accidentally caught the attention of researchers, the exact place of origin is unknown. The rare fossil is now back in Argentina.

“For me, dinosaur eggs are like time capsules that carry a message from the past, says Kundrat. “Our copy tells a story about the giants of Patagonia before they hatched. Our study reveals numerous new aspects about the embryonic period of the largest herbivore that has ever lived on our planet. We would not have expected a horned face and two-eyed vision from a Titanosaurus. ”With the help of synchrotron technology, he would like to examine further dinosaur embryos from other parts of the world in the future.

Source: Martin Kundrat (Pavol Jozef Safarik University, Kosice) et al., Current Biology, doi: 10.1016 / j.cub.2020.07.091

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