Note that the full text of both papers can be read online in Research Gate.ÂThe Norell et al. paper can also be downloaded.
Mark A. Norell, Jasmina Wiemann, Matteo Fabbri, Congyu Yu, Claudia A. Marsicano, Anita Moore-Nall, David J. Varricchio, Diego Pol & Darla K. Zelenitsky (2020)
The first dinosaur egg was soft.
Nature (advance online publication)
doi: Âhttps://doi.org/10.1038/s41586-020-2412-8
https://www.nature.com/articles/s41586-020-2412-8
The first dinosaur egg was soft.
Nature (advance online publication)
doi: Âhttps://doi.org/10.1038/s41586-020-2412-8
https://www.nature.com/articles/s41586-020-2412-8
https://www.researchgate.net/publication/342243170_The_first_dinosaur_egg_was_soft
ÂLucas J. Legendre, David Rubilar-Rogers, Grace M. Musser, Sarah N. Davis, Rodrigo A. Otero, Alexander O. Vargas & Julia A. Clarke (2020)
A giant soft-shelled egg from the Late Cretaceous of Antarctica.
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-020-2377-7
https://www.nature.com/articles/s41586-020-2377-7ÂÂ
On Wed, Jun 17, 2020 at 9:02 AM Ben Creisler <bcreisler@gmail.com> wrote:
Ben CreislerNew papers:=====Johan Lindgren & Benjamin P. Kear (2020)
Hard evidence from soft fossil eggs.
Nature (advance online publication)
https://www.nature.com/articles/d41586-020-01732-8
Free pdf:
https://media.nature.com/original/magazine-assets/d41586-020-01732-8/d41586-020-01732-8.pdf
It is thought that dinosaurs laid hard-shelled eggs, whereas ancient marine reptiles gave birth to live young. However, new discoveries of fossilized soft-shelled eggs challenge these long-held tenets of reproductive evolution.
****Mark A. Norell, Jasmina Wiemann, Matteo Fabbri, Congyu Yu, Claudia A. Marsicano, Anita Moore-Nall, David J. Varricchio, Diego Pol & Darla K. Zelenitsky (2020)
The first dinosaur egg was soft.
Nature (advance online publication)
doi: Âhttps://doi.org/10.1038/s41586-020-2412-8
https://www.nature.com/articles/s41586-020-2412-8
Calcified eggshells protect developing embryos against environmental stress and contribute to reproductive success. As modern crocodilians and birds lay hard-shelled eggs, this eggshell type has been inferred for non-avian dinosaurs. Known dinosaur eggshells are characterized by an innermost membrane, an overlying protein matrix containing calcite, and an outermost waxy cuticle. The calcitic eggshell consists of one or more ultrastructural layers that differ markedly among the three major dinosaur clades, as do the configurations of respiratory pores. So far, only hadrosaurid, a few sauropodomorph and tetanuran eggshells have been discovered; the paucity of the fossil record and the lack of intermediate eggshell types challenge efforts to homologize eggshell structures across all dinosaurs. Here we present mineralogical, organochemical and ultrastructural evidence for an originally non-biomineralized, soft-shelled nature of exceptionally preserved ornithischian Protoceratops and basal sauropodomorph Mussaurus eggs. Statistical evaluation of in situ Raman spectra obtained for a representative set of hard- and soft-shelled, fossil and extant diapsid eggshells clusters the originally organic but secondarily phosphatized Protoceratops and the organic Mussaurus eggshells with soft, non-biomineralized eggshells. Histology corroborates the organic composition of these soft-shelled dinosaur eggs, revealing a stratified arrangement resembling turtle soft eggshell. Through an ancestral-state reconstruction of composition and ultrastructure, we compare eggshells from Protoceratops and Mussaurus with those from other diapsids, revealing that the first dinosaur egg was soft-shelled. The calcified, hard-shelled dinosaur egg evolved independently at least three times throughout the Mesozoic era, explaining the bias towards eggshells of derived dinosaurs in the fossil record.***News:
https://www.amnh.org/explore/news-blogs/research-posts/first-dinosaur-eggs-were-soft-like-a-turtle-s
https://www.nationalgeographic.com/science/2020/06/first-dinosaurs-laid-soft-eggs
https://www.iflscience.com/plants-and-animals/early-dinosaurs-likely-laid-soft-turtlelike-eggs-that-evolved-at-least-three-times/
https://www.eurekalert.org/pub_releases/2020-06/amon-fde061520.php
https://www.nytimes.com/2020/06/17/science/dinosaurs-soft-eggs.html=====Lucas J. Legendre, David Rubilar-Rogers, Grace M. Musser, Sarah N. Davis, Rodrigo A. Otero, Alexander O. Vargas & Julia A. Clarke (2020)
A giant soft-shelled egg from the Late Cretaceous of Antarctica.
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-020-2377-7
https://www.nature.com/articles/s41586-020-2377-7
Egg size and structure reflect important constraints on the reproductive and life-history characteristics of vertebrates. More than two-thirds of all extant amniotes lay eggs. During the Mesozoic era (around 250 million to 65 million years ago), body sizes reached extremes; nevertheless, the largest known egg belongs to the only recently extinct elephant bird, which was roughly 66 million years younger than the last nonavian dinosaurs and giant marine reptiles. Here we report a new type of egg discovered in nearshore marine deposits from the Late Cretaceous period (roughly 68 million years ago) of Antarctica. It exceeds all nonavian dinosaur eggs in volume and differs from them in structure. Although the elephant bird egg is slightly larger, its eggshell is roughly five times thicker and shows a substantial prismatic layer and complex pore structure4. By contrast, the new fossil, visibly collapsed and folded, presents a thin eggshell with a layered structure that lacks a prismatic layer and distinct pores, and is similar to that of most extant lizards and snakes (Lepidosauria). The identity of the animal that laid the egg is unknown, but these preserved morphologies are consistent with the skeletal remains of mosasaurs (large marine lepidosaurs) found nearby. They are not consistent with described morphologies of dinosaur eggs of a similar size class. Phylogenetic analyses of traits for 259 lepidosaur species plus outgroups suggest that the egg belonged to an individual that was at least 7 metres long, hypothesized to be a giant marine reptile, all clades of which have previously been proposed to show live birth. Such a large egg with a relatively thin eggshell may reflect derived constraints associated with body shape, reproductive investment linked with gigantism, and lepidosaurian viviparity, in which a 'vestigial' egg is laid and hatches immediately.