Dinosaur egg shell. Polarised light micrograph of a transverse section through the shell of the egg of a dinosaur. At centre running obliquely are tubercles (brown) that formed protruberances on the outer shell surface. Pores between tubercles enabled the embryo to breathe. The interior (at right) and exterior of the egg is mineralised due to fossilisation. Egg diameter is about 20 centimetres and the shell thickness is roughly 1.5 millimetres. The egg was found at Bastus, South Central Pyrenees in Spain. The site is one of the richest deposits of fossilised dinosaur eggs. During the Upper Cretaceous (65-100 million years ago) it was a seashore nesting ground for dinosaur eggs. Magnification x18.5 when printed 10 centimetres wide.
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