The “Tustea Puzzle”: hadrosaurid (Dinosauria, Ornithopoda) hatchlings associated with Megaloolithidae eggs in the Maastrichtian of the Ha?eg Basin (Romania)

Abstract

Since 1991 when the coinciding occurrence of megaloolithid eggs and hatchlings of the hadrosaurid Telmatosaurus transsylvanicus was suggested by a few limb bone remains that were found close to the first discovered eggs in a vertical escarpment near the village of Tustea, several tens of eggs grouped in clutches together with embryonic and hatchling bones were unearthed from the same site, after the place was leveled and a horizontal platform was created. By their external characters and eggshell microstructure all the eggs belong to the Megaloolithus oogenus, closer to M. siruguei; similarly all the baby remains whose state of preservation allows their taxonomic assignment belong to Telmatosaurus transsylvanicus, one of the common dinosaur species from the rich Maastrichtian faunal assemblage of the Hateg Basin (Romania), considered to represent a basalmost hadrosaurid. Most of the baby remains consist of isolated bones and teeth, but partial skeletons with articulated elements were also found. The preliminary ontogenetic study reveals a rapid growth of the hatchlings, a fact also supported by the discovery of most of the skeletal remains outside of the egg clutches, but in their close vicinity. In a few cases bones were found within the egg clutches and even inside the egg. The megaloolithid eggs and the hadrosaurid baby remains represent a single/occasional level of incubation, on which neither baby nor adult sauropod remains nor other dinosaur hatchlings were found.