Acta Medica Polona 1977, 18, 4, 345-346
The eggs of reptiles and birds are found in fossil state very rarely. The Polish-Mongolian
Paleontological Expeditions to the Gobi Desert have gathered from the Upper Creataceous the
greatest in the world collection of fossil eggs. Some of the specimens belong to dinosaurs, others
to turtles, crocodilians, lizards or birds. The present paper presents preliminary information on
teratological dinosaur (?) eggs from this collection.

Material and methods. The studied material includes fragments of dinosaur (?) egg shells about
100 million years old. These shells were prepared for scanning electron microscope study using
mainly methods described in detail by H.K. Erben (
Biomineralisation 1, 1970). Moreover, the
polarizing microscope was used. The studies were done at the M.Nencki Institute of Experimental
Biology (Pol. Acad. Sci.) and Institute of Plant Culture and Acclimatization on JSM S-1 and
Stereoscan 180 electron microscopes.

Results and discussion. Eggs of teratological, double or tripple shells (Fig. 1) have been
discovered. The structure of these shells is rather different then the structure of "ovum in ovo"
from the Cretaceous of Southern France studied by H.K. Erben. In the latter case there is a
compact contact between the first and second egg shell. The teratological egg shells from the Gobi
Desert do not cling to one another compactly. There no contact between the first shell mammilary
zone and the second egg shell. An analogous situation is observed in eggs of tripple shells.
One of the egg shells found in close association with embryos, exposes the teratological double
structure (the first finding of complete embryos in fossil eggs). Further palaeohistological study
may allow to determine a degree of ossification of the embryo and clarify wheter the mentioned
double shell had made impossible the hatching of young individual. The teratological thickening of
the shell, as well as the obstruction of shell pores (Fig. 2: normal shell pore), seems to have been
genetically controlled in late Cretaceous dinosaurs. Studies on ultrastructure and
palaeobiochemistry of egg shells and their organic matrix may also clarify many problems of
taxonomic position of fossil egg shells from the Gobi desert and the bases of their teratology. This
problem is very important for explanation of dinosaur extinction.
An elongated dinosaur egg
from the Cretaceous of the Gobi Desert.
Nearly 20 cm long.
Collection of Roman Kozlowski Institute of Paleobiology.