''Polyclonoolithus'' is an oogenus of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dinosaur egg. It is from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

Gansu Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibet ...

, China. They have distinctive, branching eggshell units, which may represent the original form of spheroolithids.

Distribution

''Polyclonoolithus'' is known exclusively from Yangjiagou, a small town in

. The only known fossil specimen is from the

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

Hekou Group The Hekou Group is a geological group in Gansu Province, China. It is Early Cretaceous in age. Dinosaur body fossils have also been recovered from the Hekou Group, including the iguanodont '' Lanzhousaurus'' and the titanosaurs ''Daxiatitan'', ...

, part of the larger Lanzhou-Minhe Basin.

Discovery

Dinosaur body fossils and ichnites are common at the Hekou Group, but fossilized eggs are rare. The first fossil eggs found there were collected by

Chinese Academy of Geological Sciences The Chinese Academy of Geological Sciences (CAGS; ) is an institution that engages in geoscience research in the People's Republic of China. The academy was established in 1956 and reorganized in 1999. Administratively it is under the PRC Ministry ...

in Zhongpu in

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, but were never formally described. In

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, a team of paleontologists from the

Gansu Geological Museum Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibet ...

, the

Institute of Vertebrate Paleontology and Paleoanthropology The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...

and the Institute of Geology once again discovered fossil eggs in the Lanzhou-Minhe Basin. In

2016 File:2016 Events Collage.png, From top left, clockwise: Bombed-out buildings in Ankara following the 2016 Turkish coup d'état attempt; the impeachment trial of Brazilian President Dilma Rousseff; Damaged houses during the 2016 Nagorno-Karabakh ...

, their discovery was described as a new oogenus and oospecies, ''Polyclonoolithus yangjiagouensis,'' by Chinese paleontologists Xie Jun-Fang, Zhang Shu-Kang, Jin Xing-Sheng, Li Da-Qing, and Zhou Ling-Qi.

Description

''Polyclonoolithus'' is only known from one specimen: ZMNH M1849, an incomplete egg (made up of several fragments) housed in the Zhejiang Museum of Natural History. Due to the poor preservation, the size and shape of a complete egg are unknown, but ''Polyclonoolithus'' was likely less than in diameter. The eggshell ranges from in thickness. The cone layer has radiating structure and makes up roughly 1/7 the total width of the eggshell. ''Polyclonoolithus'' is distinctive for having branching shell units, with irregular pore canals between them. The branches of the eggshell units fuse together towards the outer surface of the shell.

Parataxonomy

''Polyclonoolithus'' is classified in its own oofamily, Polyclonoolithidae. Its branching eggshell units set it apart from all other oofamilies, except for

Dendroolithidae ''Dendroolithus'' is an oogenus of Dendroolithid dinosaur egg found in the late Cenomanian Chichengshan Formation ( Tiantai Group), in the Gong-An-Zhai and Santonian Majiacun Formations of China and the Maastrichtian Nemegt and Campanian Bar ...

Dictyoolithidae Dictyoolithidae is an oofamily of dinosaur eggs which have a distinctive reticulate organization of their eggshell units. They are so far known only from Cretaceous formations in China. Distribution All known dictyoolithids are known from the Cr ...

, and Similifaveoloolithidae. It lacks the reticulate structure seen in dictyoolithids, and unlike similifaveoloolithids and dendroolithids, the eggshell units vary in thickness. It furthermore differs from dendroolithids in that the eggshell units are not totally fused together at the outer surface of the eggshell, however this could only be due to erosion. There is also some similarity between the branching eggshell units of ''Polyclonoolithus'' to the superimposed eggshell units found in

Spheroolithidae Spheroolithidae is an oofamily of dinosaur eggs. It contains ''Guegoolithus'', ''Spheroolithus'', and '' Paraspheroolithus''. Like modern birds, the eggshell membrane formed before the calcareous part of the shell.Z.-K. Zhao. (1994) "Dinosaur egg ...

, leading to the hypothesis by Xie ''et al.'' that the shell units of polyclonoolithids may represent a primitive form of those found in spheroolithids. ''Polyclonoolithus'' contains only a single oospecies: ''P. yangjiagouensis''.

References

{{Taxonbar, from=Q22286497 Fossil parataxa described in 2016 Egg fossils Dinosaur reproduction Prehistoric animals of China Early Cretaceous dinosaurs of Asia Monotypic dinosaur genera Paleontology in Gansu