Upper Jurassic, Theropod Dinosaur nests, eggs and embryos from Pai Mogo (Lourinhã, Portugal)

At Pai Mogo, near Lourinhã, a dinosaur nest area has been recognized about 500 meters from the coastal cliffs.A lot of eggs (ca. 124 x 92 mm) and fragments were found. A few eggs still contained embryo bones that may be ascribed to a Theropod Dinosaur. The prismatic-dinosauroid type shell structure is closely similar to other egg structures from the Upper Jurassic of Colorado The same site yielded rare Theropod and fish teeth, as well as a mandible from a Paulchoffatiid Multituberculate mammal from a genus hitherto well known only from the famous Guimarota Mine (near Leiria, Portugal) locality.

Dinosaur eggs are known since long ago, at the French Pyrenees (1859) and from Provence (1869). As far as Portugal is concerned, the first discovery is due to Paul Choffat (1908) in the Upper Jurassic from Alfeizerão: a single egg in association with an Omosaurus basin.

A lot of progress has been made since then. Spectacular findings of nests and eggs have been made in Mongolia, China, Alaska, Tierra del Fuego, etc. Most of them are Cretaceous in age. Only a minority concerns older, Jurassic sediments. However, many doubts about nest-making, egg-laying, eclosion and parental care (including newborn feeding) still remain.

Uneclosed, embryo skeleton-containing eggs, or eggs in association with newborn bones are exceedingly rare. Only seldom has it been possible to correlate eggs with corresponding skeletons; most generally, it is not possible to know whose are the egg-layers. It is therefore hazardous to report any type of egg-shells to any Dinosaur family.

As Zhao (1994) states about Dinosaur eggs from China, ...as egg-shells and eggs ... occur independently from skeletons ... there is no structural correlation ..., and it is difficult to ascribe a certain egg to one or another Dinosaur taxon. Hence it is not surprising that a parataxonomy arouse, even if new discoveries were made of embryo-containing eggs, of newborn Dinosaurs and even of a Dinosaur that died while protecting a nest. In Europe, a lot of Dinosaur egg-nests with many eggs were found. However only in a single, Maastrichtian (Uppermost Cretaceous) locality in Roumania an uneclosed egg revealed (by means of tomography) some embryo remnants.

The discovery of the Pai Mogo Upper Jurassic, Theropod Dinosaur-egg site, with dozens of (some embryo-containing) eggs is therefore a most remarkable event.

Miguel Telles ANTUNES
11 June 1997

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