Geoscience Reference
In-Depth Information
and number of pores, and ornamentation on the shell's surface. At
the microscopic level, eggs are classified based on the characteristics
of crystalline units that form the shell, the structure of the pore
canals, and the chemical composition of the crystalline layers that
make up the shell. Such detailed study requires microscopes that ana-
lyze polarized light and scanning electron microscopes, also known as
SEMs, which magnify the features of the shell tens or hundreds of
thousands of times.
Based on the characteristics of the shell units, hard-shelled eggs of
living animals are divided into four basic categories: testudoid (some
turtles), geckonoid (geckos), crocodiloid (crocodiles), and omithoid
(birds). These eggs come in two main structural types: those made of
calcium carbonate crystals called aragonite (some turtles), and those
made of calcium carbonate crystals with a slightly different chemical
Main functions of an egg.