''Parvoblongoolithus'' is an oogenus of fossil dinosaur egg whose small size and unusual shape suggest the possibility that it is a dwarf egg.

Distribution

The sole known ''Parvoblongoolithus jinguoensis'' specimen was found in the

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

Chichengshan Formation in Tiantai County,

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by Jiang ...

Description

''Parvoblongoolithus'' known from only a single specimen. It is relatively small (measuring long by wide) with an asymmetrical shape, similar to modern bird eggs. The eggshell is 1.12 mm thick, with the barrel-shaped cones of the mammillary layer making up one-fifth of the total eggshell thickness. The pore system is prolatocanaliculate, meaning the pores vary in width along their length. The pore canals are thick and irregularly shaped. The outer surface of the eggshell is smooth. Despite having a bird-like shape and size, the ''P. jinguoensis'' has a very different microstructure, which bears a closer resemblance to non-avian dinosaur eggs than bird eggs. Most significantly, all known Cretaceous bird eggs have a three-layered eggshell, whereas the eggshell of ''Parvoblongoolithus'' is two-layered. Additionally, its pore system is prolatocanaliculate, unlike the angusticanaliculate pores of bird eggs (such as Laevisoolithidae or Gobioolithidae) and its microstructures are much more similar to those of stalicoolithids, ''

Mosaicoolithus ''Mosaicoolithus'' is an oogenus of fossil egg from the Cenomanian Chichengshan Formation ( Tiantai Group) and Albian to Cenomanian Laijia Formation ( Qujiang Group) of Tiantai County, Zhejiang Province in China. Its classification is uncertain. ...

'', and '' Paraspheroolithus''.

Palaeobiology

Since no skeletal remains were associated with its remains, the parentage of ''Parvoblongoolithus'' is unknown. However, its microstructure suggests it was laid by some kind of non-

avian Avian may refer to: *Birds or Aves, winged animals *Avian (given name) (russian: Авиа́н, link=no), a male forename Aviation *Avro Avian, a series of light aircraft made by Avro in the 1920s and 1930s *Avian Limited, a hang glider manufacture ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

, related to the parents of Stalicoolithidae, ''Paraspheroolithus'', or ''Mosaicoolithus''. ''Parvoblongoolithus'' is remarkable for having an extremely thick shell (as thick as the shell of

titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...

eggs) despite being significantly smaller than its close relatives. This would have made it much more difficult for a baby dinosaur to break out of the egg without parental assistance. It is possible that ''Parvoblongoolithus'' actually represents a fossil dwarf egg, a type of deformity occasionally observed in modern birds when a disturbance of the oviducts causes them to form a small, deformed egg. This would explain both the thick eggshell and unique shape of ''P. jinguoensis''.

Parataxonomy

''Parvoblongoolithus'' has not been classified into any oofamily. The eggshell resembles the spherulitic type, but it lacks the radial-tabular ultrastructure. It is closely related to ''Paraspheroolithus'', ''Mosaicoolithus'', and stalicoolithids.

References

{{Taxonbar, from=Q22285703 Fossil parataxa described in 2015 Dinosaurs of Asia Egg fossils