User:Ashorocetus/sandbox/Turtle Egg

Turtle eggs are the eggs laid by turtles.

Physical characteristics
Turtle eggs vary greatly in size and shape.

Egg and clutch size are also highly variable, even among members of a single turtle species. For example, a young female turtle may lay fewer and smaller eggs than an older turtle. In some turtles, like Dermochelys coriacea, a female will lay, in a single clutch, multiple large, viable eggs, interspersed with small yolkless eggs. Possibly, this is to increase the space between the viable eggs to improve their gas exchange.

Shell
Unlike other hard-shelled amniotic eggs, the calcareous layer of turtle eggs is composed of aragonite instead of calcite. While all turtle eggs have a calcerous shell, it is not necessarily solid. Eggshells range from highly flexible to rigid. Among modern turtles, chelonioids, emydids, and some pleurodires have highly pliable eggshells. Chelydrids have moderately pliable eggshells, and carettochelyids, geoemydids, kinosternoids, testudinids, and trionychids have rigid eggshells.

Like avian and crocodilian eggs, the shell of turtle eggs is composed of a fibrous membrane covered with a layer of thousands of microscopic calcium carbonate crystals, called shell units.

As fossils
Fossil turtle eggs are the fossilized eggs of turtles.

Classification
Since it is usually unknown which species laid fossil eggs, they are classified according to a parataxonomic system parallel to Linaean taxonomy, with rankings of Basic Type, Morphotype, Oofamily, Oogenus, and Oospecies. Turtles eggs correspond to the Testudoid basic type. They are divided up into to morphotypes: Spheruflexibilis and Spherurigidis, corresponding to the oofamilies Testudoflexoolithidae and Testudoolithidae, respectively. Spheruflexibilis represents turtle eggs with a pliable shell, whereas Spherurigidis is the eggs with a rigid shell.

Unfortunately for cladistic analysis, turtle eggs have a large degree of homoplasy, and only a few characters are phylogenetically informative.

The oospecies-level parataxonomy of fossil turtle eggs (Testudoid basic type) Testudoflexoolithus