Uppermost Cretaceous megaloolithid eggs from the Haţeg Basin, Romania, associated with hadrosaur hatchlings: Search for explanation

摘要: Abstract Four localities in the Upper Cretaceous (Maastrichtian) of Haţeg Basin (in order discovery, Tustea, Totesti-baraj, Nălaţ-Vad and Livezi) have yielded clutches megaloolithid eggs. Egg morphology size, eggshell thickness, external ornamentation internal microstructure, pore density geometry, as well (where this could be observed) are all similar among four localities, allowing assignment eggs to Megaloolithus cf. siruguei . Most egg occurrences related paleosols variable chemical composition maturity, developed within different parts floodplain. The nesting horizon from Tustea was partially reconstructed on a 160 m 2 surface, thorough analysis taphonomy clutches. It has also hatchling remains at ontogenetic developmental stages, even, more rarely, embryo well. bones occur vicinity or even clutches; single case, incompletely ossified embryonic skeletal remains, including dentary tooth, were found inside an incomplete egg. Without exception, neonate belong basal hadrosaurid Telmatosaurus transsylvanicus , one common dinosaur species faunal assemblage. No sauropod Tustea; only fragmentary pelvic girdle caudal vertebrae adult titanosaurian unearthed recently 20 cm above horizon. None other three provided neonatal any species. Despite general consensus that oogenus belongs exclusively sauropods, co-occurrence seems contradict view. Previous cladistic analyses dinosauroid ootaxa might offer explanation controversial issue. These revealed Megaloolithidae appears sister group Spheroolithidae, usually regarded family. Perhaps significant amount homoplasy is present evolution dinosaurian eggs, whose structure depends incubation environment biology physiology reproductive system itself, oospecies been laid by higher-level taxa, both sauropods (basal) hadrosaurids. Understanding significance paraphyletic distribution requires further study.