Jehol fossils from the Jiaolai Basin of Shandong, North China: review and new perspectives

Starting in the early 1950s, paleontologists began to discover a wide range of Cretaceous terrestrial fossils in the Laiyang, Qingshan, and Wangshi groups of the Jiaolai Basin which resides in the eastern part of the Shandong Peninsula of northern China. Significant specimens from these deposits include various dinosaur eggs, footprints, and fossils including hadrosauroids, tyrannosaurids, and ankylosaurids. These expanded understanding of evolution, biodiversity, and paleoecology in East Asia. While many examples of the Jehol Biota from this area are not well constrained in terms of their stratigraphy and geochronology, previous studies have generally suggested that fossils from this region represent the second or third phase of Jehol Biota development. This paper reviews fossils, stratigraphic correlations, tectonic history, and age estimates for the less well-studied outcrops of the Shandong Peninsula that host Jehol Biota. We report three new 40Ar/39Ar ages for the Qingshang Group and discuss how these somewhat imprecise ages still constrain chronostratigraphic interpretation for the fossil-rich units.

The first dinosaur egg remains a mystery

A recent study by Norell et al. (2020) described new egg specimens for two dinosaur species, identified as the first soft-shelled dinosaur eggs. The authors used phylogenetic comparative methods to reconstruct eggshell type in a sample of reptiles, and identified the eggs of dinosaurs and archosaurs as ancestrally soft-shelled, with three independent acquisitions of a hard eggshell among dinosaurs. This result contradicts previous hypotheses of hard-shelled eggs as ancestral to archosaurs and dinosaurs. Here we estimate the ancestral condition for dinosaur and archosaur eggs by reanalyzing the original data from Norell et al. and that from a recent study on reptile eggshells (Legendre et al., 2020) with the addition of these new dinosaur specimens. We show that the recovery of dinosaur eggs as ancestrally soft-shelled is conditioned by the discretization of a continuous character (eggshell thickness), the exclusion of turtle outgroups from the original sample, and a lack of branch length information. When using a larger sample, calibrated trees, and a definition of hard-shelled eggs referencing their unique prismatic structure, we recover dinosaur and archosaur eggs as either hard-shelled or uncertain (i.e. equal probability for hard- and soft-shelled). This remaining ambiguity is due to uncertainty in the assessment of eggshell type in two dinosaur species, i.e. ∼1% of the total sample. We conclude that more reptile egg specimens and a strict comparative framework are necessary to decipher the evolution of dinosaur eggs in a phylogenetic context.

Dinosaur Eggs Associated with Crustacean Trace Fossils from the Upper Cretaceous of Jiangxi, China: Evidence for Foraging Behavior?

We report the discovery of concentrated invertebrate inchnofossils in close association with a dinosaur nest from the Hekou Formation in Jiangxi Province, China. The seven dinosaurian eggs reported clearly belong to the Elongatoolithidae and burrow traces were most likely made by small crustaceans. This association prompts the question as to whether invertebrate activity had relations with the buried eggs. This may be just an occasional case or the eggs may have organically increased the content of organic matter in soil which attracted the crustaceans.

A new terrestrial trace fossil Feoichnus martini n. isp. from the Upper Cretaceous Two Medicine Formation (USA)

A new trace fossil, Feoichnus martini new ichnospecies, from the Two Medicine Formation is here described. This ichnotaxon is reported from the upper Campanian deposits of the Egg Mountain locality (Montana) and consists of a hemispherical to hemiellipsoidal structure with a truncated upper edge, and a regular, rounded lower edge marked by a lined border composed of stained layers. The trace maker likely impregnated the border using organic fluids. The simple lined wall observed in F. martini n. isp. suggests that the structure was produced by an invertebrate soil-dwelling organism, likely an insect. Specimens are preserved as casts in calcitic Inseptisols alongside an abundant vertebrate fossil record composed by dinosaurian and nondinosaurian fossil remains, dinosaur eggs and nest structures, and pervasive insect bioturbation. Feoichnus martini n. isp. represents an additional, minor component of the impoverished Celliforma ichnofacies reported at Egg Mountain and expands the paleogeographical distribution of the ichnogenus Feoichnus Krause et al., 2008 to the Upper Cretaceous deposits of Montana, USA.UUID: http://zoobank.org/7c1a5026-7f27-4f12-a9fb-1eb8daa93baf