User:Ashorocetus/sandbox/Spheroolithus

Spheroolithus is an oogenus of dinosaur egg.

Description
Speroolithus eggs are roughly spherical eggs ranging from 7 to 12 cm long, with an eggshell 1-3 millimeters thick. Their shape is variable, even within a single clutch. The eggshell thickness can also vary significantly in a single egg. Because of this, distinguishing oospecies is difficult and at times imprecise. The ornamentation on the outer surface is variable; in most oospecies it is smooth or exhibits the sagenotuberculate pattern, meaning that the shell is covered with a netlike pattern of ridges interspersed with pits and nodes.

The eggshell consists of a single structural layer made up of tiny calcite crystal units. As in all spheroolithids, these shell units are fan-shaped and typically fuse together towards the outer edge of the eggshell. The pore canals are of the prolatocanaliculate type, meaning that they are wide with an extremely irregular shape and variable width along their length. %This type of pore system has allows gases to pass through the eggshell relatively easily, which typically associated with humid incubation conditions%.

Oospecies
Paleontologists do not all agree about which oospecies should be included in Sphereoolithus. Most inclusively, Spheroolithus contains eight oospecies:
 * S. albertensis
 * S. chiangchiungtingensis
 * S. choteauensis
 * S. europaeus'
 * S. megadermus
 * S. maiasauroides - Since Spheroolithus was described, the assignment of S. maiasauroides to it has been tentative. Mikhailov (1997) notes that it shows some similarity to dendroolithid eggshells.
 * S. tenuicorticus
 * S. irensis
 * S. zhangtoucaoensis
 * S. jincunensis

History
Spheroolithus has a somewhat convoluted taxonomic history. The oogenus was first named in 1979 by the Chinese paleontologist Zhao Zikui to contain the oospecies S. chiangchiuntingensis and tentatively including S. megadermus. At that time, Zhao also named Paraspheroolithus and Ovaloolithus, which he included in the oofamily Spheroolithidae. In 1991, the Russian paleontologist Konstantin Mikhailov created the modern classification system for fossil eggs, with nomenclature based on Zhao's system. However, Mikhailov did not consider Spheroolithus and Paraspheroolithus different enough to warrant their classification as separate oogenera, and according to his system, so he included Zhao's Paraspheroolithus irenensis in Spheroolithus as S. irenensis. In later publications, Mikhailov considered S. irenensis to be the type oospecies of the oogenus.