Dinosaurs nesting on tidal flats

The discovery of a dinosaur clutch in Upper Cretaceous tidal flat deposits in the Tremp Formation in Biscarri, Isona (Lleida, Spain), provides insight into the mode of life of some dinosaurs. The clutch occurs in grey marls that were originally waterlogged, muddy sediments. The seven elongated eggs are parallel to each other and with their long axis almost vertically oriented. A mound-nest is inferred in contrast to hole-nest described so far for similar eggshell types. The permeability of the eggshell (oospecies Megaloolithus siruguei) was highly enhanced by a braided network of multicanaliculate pore canals. The nest style, eggshell porosity and tidal flat environment point to a periaquatic habitat for these dinosaurs. A modern analogue occurs in crocodiles, alligators and some birds living in periaquatic environments, with nesting on plant-mounds above waterlogged soils or even on floating vegetation. (C) 2000 Elsevier Science B.V. All rights reserved.