The 'missing link' which proves the relationship among dinosaurs and birds may have been found.
It is a widely-held view that dinosaurs and birds share the same heritage, and an egg exposed in the Montsec area of Lleida, near Catalonia in Eastern Spain, shares individuality of both species.
The dinosaur egg, dating back 70 to 83 million years, has an oval shape, similar in exterior to a chicken egg, and an 'air bag' inside which birds today use to respire in the last stages of its growth.
The new type of dinosaur egg has been given the technical name of Sankofa pyrenaica and is the only dinosaur egg in the world to have an oval shape, alike to that of chicken eggs.
Nieves López Martínez, palaeontologist of the Complutense University of Madrid, was working on investigate of dinosaur eggs before her death in December 2010.
Together with Enric Vicens, palaeontologist of the Universitat Autònoma de Barcelona, the two scientists conducted a thorough analysis of their detection, now published in the journal Palaeontology.
The South Pyrenean area is rich in dinosaur egg sites, most of which communicate to sauropod eggs from the upper Cretaceous, dating back more than 70 million years ago.
During that period, the area was a coastal area full of beaches and deltas which won land from the sea through residue buildup.
Sand and mud from that period gave way, millions of years later, to the stonework and marl where dinosaur leftovers now can be found. On the seashore ridges and flat coastal lands is where a large group of dinosaurs laid their eggs.
The sites anywhere the discoveries were made correspond to the upper Cretaceous, between the Campanian and Maastrichtian periods, some 70 to 83 million years ago.
The fossils found belong to small eggs measuring some 7 centimeters tall and 4 cm wide, while the eggshell was on standard 0.27mm thick.
Most of the eggs found were broken in small wreckage, but scientists also discovered more or less complete eggs, which can be easily deliberate in sections.
The eggs found at the sites all belong to the same species. The main difference when compare to other eggs from the same period is their irregular shape, similar to that of chicken eggs.