Paleontologists in China have unearthed and examined three adult skeletons and five clutches of embryonic eggs containing Qianlong shouhu, a previously unknown species of sauropodomorph dinosaur from the Early Jurassic. Most significantly, these fossils provide strong evidence of the earliest known leathery eggs.
Qianlong shouhu It lived in what is now China during the Early Jurassic era, between 200 and 193 million years ago.
The dinosaur belongs to sauropodomorpha group of long-necked, herbivorous dinosaurs that includes the largest animals to ever walk the Earth.
The ancient creature was approximately 6 m (20 ft) long and weighed around 1 ton.
The fossilized remains of Qianlong shouhu – three adult skeletons and five clutches of eggs – were found in the Ziliujing Formation in southwest China’s Guizhou province.
“Embryos show some differences from adults, for example, a proportionally longer skull, a more vertical anterior margin of the snout and fewer teeth,” said the paleontologist from the China University of Geosciences. Fenglu Han and colleagues.
“Allometric analyzes of limb proportions between adult and embryonic specimens indicate that adults Qianlong shouhu “It could walk on its hind legs, but the babies were probably quadrupeds.”
“The general taphonomic and sedimentary characteristics indicate that Qianlong shouhu may have practiced colonial nesting as a reproductive behavior, similar to other basal sauropodomorphs, including Massospondylus and musaurus.”
According to the team, Qianlong shouhu It had relatively large eggs with a relatively thick calcareous shell formed by prominent mammillary cones compared to other early-diverging sauropodomorph dinosaurs.
“Our results show that Qianlong shouhu “It possessed eggshell microstructures similar to other Cretaceous dinosaur egg fossils, which likely consisted of two layers, the mammillary layer and the continuous layer, and had fully developed eggshell units,” the researchers said.
“The calcareous layer of Qianlong shouhu The eggs were much thicker than those of most soft-shelled eggs, but thinner than those of hard-shelled eggs.”
“Comparison of eggshell fragmentation between different shell types also suggests that the surface of the eggshell Qianlong shouhu It had small fragments, similar to the shell of a leathery egg, in contrast to the folded surface of soft-shelled eggs or the large, fragmented surface of hard-shelled eggs.
These observations indicate that Qianlong shouhu They laid leathery eggs.”
To test the macroevolutionary patterns of selected reproductive traits across the dinosaur-bird transition, the scientists pooled data from 210 living and fossil species representing all major reptile clades and tested evolutionary trends using multiple time-scale phylogenies.
“The most significant increase in egg size occurred early in theropod evolution.”
“In terms of eggshell thickness, we found that thickness tended to decrease from the base of archosaur to the base of Saurischia, followed by a significant increase in eggshell thickness early in theropod evolution.” . “There was also an increasing trend in eggshell thickness in the evolution of sauropodomorphs.”
“The egg shape was generally conserved in the evolution of diapsids into living birds. For example, although theropod egg elongation peaked in oviraptorosaurs (with the greatest egg elongation among diapsids), it would later return to its ancestral state.”
“As a result, all crown bird clades inherited only slightly elongated eggs.”
“Overall, the reconstruction of the ancestral state of various types of eggshells supports the conclusion that the first dinosaur egg was probably leathery, relatively small and elliptical.”
This research is described in a paper In the diary National Science Magazine.
Fenglu Han et al. Exceptional Early Jurassic fossils with leathery eggs shed light on the reproductive biology of dinosaurs. National Science Magazine, published October 9, 2023; doi:10.1093/nsr/nwad258