Pachycorioolithus

Pachycorioolithus Temporal range: Albian PreꞒ Ꞓ O S D C P T J K Pg N
Egg fossil classification
Oofamily:	†Pachycorioolithidae Lawver et al., 2016
Oogenus:	†Pachycorioolithus Lawver et al., 2016
Oospecies
†P. jinyunensis Lawver et al., 2016 (type)

Pachycorioolithus is an

Pachycorioolithus is represented in the fossil record by a single, 80% complete fossil egg. It is elongated, measuring 50 mm (2.0 in) long by 32 mm (1.3 in) across, and smooth-surfaced. Thin pores (20 to 30 µm in diameter) cut through the eggshell.[1]

The eggshell is very thin, measuring only 166 

Though no embryo was found in the egg, Pachycorioolithus can be referred to Theropoda by the characteristics of its eggshell. However, it is uncertain whether the parent was a bird or not.^[1] Most non-avian dinosaurs have a two- or one-layered eggshell, whereas birds typically have a three-layered eggshell (like Pachycorioolithus).^[2] However, most Mesozoic bird eggs have only two layers^[1] and some non-avian dinosaur eggs have three layers, so this trait alone cannot be used to identify bird eggs.^[3] Lawver et al. (2016) believed it likely that P. jinyunensis pertains to a bird because of its small size and extremely thin shell, but they could not exclude the possibility that it was laid by a small, non-avian, theropod.^[1]

Distribution

The only known P. jinyunensis specimen was discovered in a quarry near Shuhong, a town in Jinyun County in Zhejiang. This site is part of the Liangtoutang Formation, dating to the Albian.^[1]

Discovery and Naming

Pachycorioolithus was first described in 2016 by a team of paleontologists consisting of Daniel R. Lawver and Frankie D. Jackson of the Montana State University, Jin Xingsheng of the Zhejiang Museum of Natural History, and Wang Qiongying of the Jinyun Museum. It was based on a single egg specimen housed in the Jinyun Museum. They gave it the name Pachycorioolithus jinyunensis, from the Greek "pachys" (thick) and "corys" (helmet), a reference to its thick outer layer, combined with "oolithus", the standard suffix for oogenus names, meaning "stone egg".^[1] The specific epithet means "from Jinyun", the county where it was found.^[1]

References