An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures

Despite the discovery of many dinosaur eggs and nests over the past 100 years, articulated in-ovo embryos are remarkably rare. Here we report an exceptionally preserved, articulated oviraptorid embryo inside an elongatoolithid egg, from the Late Cretaceous Hekou Formation of southern China. The head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo. Comparison to other late-stage oviraptorid embryos suggests that prehatch oviraptorids developed avian-like postures late in incubation, which in modern birds are related to coordinated embryonic movements associated with tucking — a behavior controlled by the central nervous system, critical for hatching success. We propose that such pre-hatching behavior, previously considered unique to birds, may have originated among non-avian theropods, which can be further investigated with additional discoveries of embryo fossils

Eggshell geochemistry reveals ancestral metabolic thermal regulation in Dinosauria

Studying the origin of avian thermoregulation is complicated by a lack of reliable methods to measure body temperatures in extinct dinosaurs. Evidence from bone histology and stable isotope analysis often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition (δ18O) of body water. By contrast, clumped isotope (Δ47) paleothermometry, which relies on the binding of 13C to 18O, provides a robust tool for determining the body temperatures of dinosaurs, but has yet to be applied across a broad phylogenetic range while accounting for the influence of paleoenvironmental conditions. Applying this method to well-preserved fossil eggshells, we find that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although these conclusions are provisional in light of uncertainties in the taxonomic assignment of dwarf titanosaur eggshell. Regardless, our results reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria.

Studying the origin of avian thermoregulation is complicated by a lack of reliable methods for measuring body temperatures in extinct dinosaurs. Evidence from bone histology and stableisotopes often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition (δ18O) of body water. Clumped isotope (Δ47) paleothermometry, based on binding of 13C to 18O, provides a more robust tool, but has yet to be applied across a broad phylogenetic range of dinosaurs while accounting for paleoenvironmental conditions. Applying this method to well-preserved fossil eggshells demonstrates that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although this conclusion isprovisional, given current uncertainties in taxonomic assignment of dwarf titanosaur eggshell. Our results nevertheless reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria

Studying the origin of avian thermoregulation is complicated by a lack of reliable methods for measuring body temperatures in extinct dinosaurs. Evidence from bone histology and stableisotopes often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition (δ18O) of body water. Clumped isotope (Δ47) paleothermometry, based on binding of 13C to 18O, provides a more robust tool, but has yet to be applied across a broad phylogenetic range of dinosaurs while accounting for paleoenvironmental conditions. Applying this method to well-preserved fossil eggshells demonstrates that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although this conclusion isprovisional, given current uncertainties in taxonomic assignment of dwarf titanosaur eggshell. Our results nevertheless reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria

Evidence for heterothermic endothermy and reptile-like eggshell mineralization in Troodon, a non-avian maniraptoran theropod

The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ47 and Δ48) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon, modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiological differences in the reproductive systems between Troodon, reptiles, and birds. Troodon and modern reptiles mineralize their eggshells indistinguishable from dual clumped isotope equilibrium, while birds precipitate eggshells characterized by a positive disequilibrium offset in Δ48. Analyses of inorganic calcites suggest that the observed disequilibrium pattern in birds is linked to an amorphous calcium carbonate (ACC) precursor, a carbonate phase known to accelerate eggshell formation in birds. Lack of disequilibrium patterns in reptile and Troodon eggshells implies these vertebrates had not acquired the fast, ACC-based eggshell calcification process characteristic of birds. Observation that Troodon retained a slow reptile-like calcification suggests that it possessed two functional ovaries and was limited in the number of eggs it could produce; thus its large clutches would have been laid by several females. Dual clumped isotope analysis of eggshells of extinct vertebrates sheds light on physiological information otherwise inaccessible in the fossil record

Fossil eggs and eggshell fragments from the Oldman Formation (Upper Cretaceous; Campanian) southern Alberta, Canada

Bibliography: p. 110-118

Description and phylogenetic implications of extant and fossil oologic remains

Bibliography: p. 234-251Some pages are in colour.Rigorous analytical techniques are combined with phylogeneticsystematic methodology to provide a new perspective on the scientific informativeness of the eggs and eggshells of both extant and extinct dinosaurs. Re-description of the eggs of paleognathous birds reveals that numerous eggshell characteristics were overlooked by previous investigators. A cladistic analysis of discrete egg characters of paleognaths reveals that although trees based on egg data provide less resolution among taxa than those based on skeletal data, egg data do provide phylogenetic information and can help resolve disagreements in relationships derived from skeletal data. In an analysis based on the egg data alone, tinamous are basal among paleognaths, Apteryx is basal among ratites and the sister taxon of an unresolved clade consisting of large ratites, within which Aepyornis and dinornithids form a subclade and Casuarius and Dromaius form a subclade. When the egg data are combined with the skeletal data of Bledsoe (1988), the clade of Apteryx, Casuarius, and Dromaius is dissolved, and Apteryx moves to a basal position within Ratitae. Analysis of 13 absolute measurements and ratios from the eggs reveals that only 4 of these continuous characters are suitable for cladistic analysis. A cladistic analysis of the continuous and discrete characters provides further resolution among taxa within the tree based on egg data in that Struthio and Rhea form a clade. Fossil eggs of several dinosaurs (including birds) are described and included in a cladistic analysis of 24 ootaxa, the results of which, in general, are comparable to those drawn from skeletal-based studies. Sauropod eggs are basal in Saurischia, allosauroid eggs are basal in Theropoda, the eggs of oviraptorids and dromaeosaurids form a derived clade, and the eggs of troodontids and birds form a clade. Unexpected results include the basal position of therizinosaurid eggs, a clade consisting of Protoceratopsidovum (Protoceratops eggs) and troodontid eggs, and a clade consisting of Deinonychus and oviraptorid eggs. These anomalies may call the alleged parentage of these eggs into question. The evolutionary-systematic method that was used to construct the traditional parataxonomic system for fossil eggs is eschewed, and a new nomenclatural system employing a phylogenetic-systematic methodology is proposed. Phylogenetic definitions are erected for seven ooclades of Saurischia, following the tenets of phylogenetic nomenclature