|University of Bristol|
Theropod eggs are known from the Upper Cretaceous of Montana, Egg Mountain and from the Flaming Cliffs of the Gobi Desert.
In Montana the eggs previously attributed to Orodromeus are now thought to belong to Troodon, a small theropod close to the origin of the birds, weighing only 100 pounds. The eggs are elongated and are about 12 cm long. The eggshell type is ornithoid, more specifically ratite, where the
upper part of the shell has no structure. The eggshell is typically thin, only 1.2-1.3 mm thick (Varricchio, 1997).
The eggshells of the theropod Oviraptor (previously attributed to Protoceratops) are known from the Flaming Cliffs of Mongolia.
Below; a skeleton of Oviraptor philoceratops from the Gobi desert.
Oviraptor eggs are elongated and elliptic in shape, with an enlarged blunt end.
Below; Oviraptor type eggs.
The surface is ornamented with distinct nodes and short ridges, arranged longitudinally to the axis of the egg, that look like fused nodes. These ridges are sub-parallel to one another. The shell is roughly 0.95 mm thick. These eggs are known as Elongatoolithus (Dong 1995).
Longitudinal striations seen in Oviraptor eggs.
Therizinosaurs are strange dinosaurs from Mongolia and China, recognised now as unusual theropods. They have elongated claws on the hand, the purpose of which is unknown. Eggs attributed to therizinosaurs are found from Cretaceous sediments of Mongolia.
Therizinosaur eggs sometimes enclose embryos. Two main types of embryo have been found:
- The Manning Egg.
- The Louie Egg.
The Manning egg (after Terry Manning) is an 8 cm diameter egg. It is spherical and contains a mix of embryo fragments. The Louie egg is somewhat of a paradox as it is an elongated egg. The embryo also has a different skin texture. Perhaps one of the embryos has been wrongly assigned to therizinosaurs.
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