Abstract:
The macro- and microstructure, elemental composition, and crystallographic
characteristics of the eggshell and eggshell membranes of the Crocodylus niloticus
eggwas investigated using optical and electron microscopy, energy-dispersive
X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD) and computerised
tomography. The translucent ellipsoid egg is composed of two basic layers,
the outer calcified layer referred to as the shell and an inner organic fibre layer,
referred to as the shell membrane. The outer inorganic calcite shell is further
divided into an external, palisade and mammillary layers with pore channels
traversing the shell. The external layer is a thin layer of amorphous calcium
and phosphorus, the underlying palisade layer consist of irregularwedge-shaped
crystals composed calcite with traces of magnesium, sodium, sulphur and phosphorus.
The crystals are mostly elongated, orientated perpendicular to the shell
surface ending in cone-shaped knobs, which forms the inner mammillary layer.
The elemental composition of the mammillae is like that of the palisade layer, but
the crystal structure is much smaller and orientated randomly. The highest number
of mammillae and shell pores are found at the equator of the egg, becoming
fewer towards the egg poles. The shell thickness follows the same pattern, with
the thickest area located at the equator. The eggshell membrane located right
beneath and embedded in the mammillary layer of the shell; it is made up of
unorganised fibre sheets roughly orientated at right angles to one another. Individual
fibres consist of numerous smaller fibrils forming open channels that run longitudinally through the fibre.
