The discovery of Qianlong shouhu, a new dinosaur types, has led to the discovery that the first dinosaur eggs were most likely leathery. This contributes considerably to our understanding of dinosaur reproductive development and the ancestral state of reptilian eggshells. (Reconstruction of egg nests consisting of fossilized embryos.) Credit: NICE Vistudio
A current study on the freshly discovered Qianlong shouhu, an early Jurassic sauropodomorph, recommends that the earliest dinosaur eggs had leatherlike shells. This finding, derived from detailed analyses of dinosaur fossils, indicates substantial evolutionary modifications in dinosaur egg morphology. The study also contributes to our understanding of the ancestral reproductive traits of numerous reptilian clades.
Dinosaur Reproductive Biology
The discovery of several remarkably preserved reproduction-related dinosaur specimens over the last 3 decades has actually enhanced our knowledge of dinosaur reproductive biology. However, due to restricted fossil evidence and an absence of quantitative analysis on a broad phylogenetic scale, much about dinosaur reproduction remained unclear, specifically pre-Cretaceous evolutionary history.
Breakthrough in Egg Morphology Research
Now, however, a current fossil discovery by scientists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences (CAS), as well as associated analyses, suggests that the very first dinosaur egg was tough, and the significant transition in egg morphology took place early in the development of theropod dinosaurs rather than near the origin of birds.
Skeletal reconstructions of adult and juvenile Qianlong. Credit: IVPP
Discovery of Qianlong Shouhu
The study, which was recently released in the National Science Review, reports the discovery of specimens of a brand-new early Jurassic early-diverged sauropodomorph dinosaur species in Guizhou, China– Qianlong shouhu– consisting of three skeletons from adult people and five egg clutches. This discovery may represent the earliest fossil record of the association in between adult dinosaurs and nests, and the types name reflects this association: Qianlong suggests “Guizhou dragon,” while shouhu suggests “guarding”– a reference to the preservation of adult skeletal fossils in association with embryo-containing egg fossils.
Qianlong was a medium-sized basal sauropodomorph dinosaur that weighed one ton and had to do with 6 meters long. The embryos show some distinctions from the adults, e.g., a proportionally longer skull, a more vertical anterior margin of the snout, and less teeth.
Contrast of fossil eggs (c) with existing soft-shelled, leathery, and hard-shelled eggs. Credit: IVPP
Insights into Qianlong Behavior and Anatomy
Allometric analyses of limb ratios in between the embryonic and adult specimens suggest that adult Qianlong was able to stroll on its hindlimbs, but the children were likely quadrupedal. The basic taphonomical and sedimentary features show that Qianlong may have practiced colonial nesting as a reproductive behavior, similar to other basal sauropodomorphs including Massospondylus and Mussaurus.
The scientists also analyzed the eggshell microstructure of Qianlong using multiple techniques, consisting of histological thin-sectioning, electron backscatter diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. The results showed that Qianlong possessed eggshell microstructures comparable to other Cretaceous dinosaur egg fossils, which likely included 2 layers– the mammillary layer and constant layer– and had actually fully established eggshell units. The calcareous layer of Qianlong eggs was much thicker than that of most soft-shelled eggs but thinner than that of hard-shelled eggs. The comparison of eggshell fragmentation among various eggshell types also suggests that the eggshell surface of Qianlong featured little pieces, comparable to a leatherlike eggshell, in contrast with the folded surface area of soft-shelled eggs or the large-fragmented surface of hard-shelled eggs. These observations indicate that Qianlong laid leathery eggs.
Summary of ancestral eggshell type for major nodes with the maximum posterior probabilities in all ASR analyses. Credit: IVPP
Evolutionary Trends in Dinosaur Eggs
In order to check the macroevolutionary patterns of picked reproductive qualities throughout the dinosaur– bird shift, the researchers assembled information from 210 fossil and extant types representing all major reptilian clades and checked evolutionary trends utilizing several time-scaled phylogenies.
They found that relative egg size reduced from the base of the Diapsida to that of the Saurischia but displayed an increasing trend from early theropods to the crown bird node. In terms of eggshell thickness, they discovered that thickness tended to reduce from the base of the archosaur to the base of the Saurischia, followed by a considerable increase in eggshell thickness early in theropod evolution.
Egg shape was generally saved in the evolution of diapsids to living birds. Although theropod egg elongation reached its peak in oviraptorosaurs– with the greatest egg elongation among diapsids– it would later return to its ancestral state. As a result, only somewhat elongated eggs were inherited by all crown bird clades.
All in all, reconstruction of the ancestral state of numerous eggshell types supports the conclusion that the very first dinosaur egg was most likely tough, relatively small, and elliptical. A tough eggshell was most likely the ancestral state of Avemetatarsalia, Archosauria, and Testudines.
Referral: “Exceptional Early Jurassic fossils with tough eggs clarified dinosaur reproductive biology” by Fenglu Han, Yilun Yu, Shukang Zhang, Rong Zeng, Xinjin Wang, Huiyang Cai, Tianzhuang Wu, Yingfeng Wen, Sifu Cai, Chun Li, Rui Wu, Qi Zhao and Xing Xu, 9 October 2023, National Science Review.DOI: 10.1093/ nsr/nwad258.
The discovery of Qianlong shouhu, a brand-new dinosaur types, has actually led to the revelation that the very first dinosaur eggs were likely leathery. The results revealed that Qianlong had eggshell microstructures similar to other Cretaceous dinosaur egg fossils, which likely consisted of two layers– the mammillary layer and continuous layer– and had completely established eggshell systems. The calcareous layer of Qianlong eggs was much thicker than that of most soft-shelled eggs however thinner than that of hard-shelled eggs. The contrast of eggshell fragmentation amongst various eggshell types likewise recommends that the eggshell surface of Qianlong featured small fragments, similar to a leathery eggshell, in contrast with the folded surface area of soft-shelled eggs or the large-fragmented surface area of hard-shelled eggs. Although theropod egg elongation reached its peak in oviraptorosaurs– with the biggest egg elongation amongst diapsids– it would later return to its ancestral state.