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Phaceloolithus; Temporal range: Late Cretaceous PreꞒ Ꞓ O S D C P T J K Pg N
Egg fossil classification
Basic shell type:	†Dinosauroid-spherulitic
Oofamily:	†Phaceloolithidae; Zeng & Zhang, 1979
Oogenus:	†Phaceloolithus; Zeng & Zhang, 1979
Oospecies
	†P. hunanensis Zeng & Zhang 1979 (type);

Phaceloolithus is an oogenus of dinosaur egg found in the Fenshui'ao Formation of the Dongting Basin of the Hunan Province of China. The eggs have a subspherical shape, measuring up to 168 mm on the long axis, and having a very thin shell.^[1]^[2]

Distribution

Phaceloolithus is found at the Dongting Basin in Hunan. They are dated, on the basis of other fossil eggs, ostracods (seed shrimp), and charophytes (algae) found at the same site, to the late Cretaceous.^[1]

Description

Phaceloolithus is nearly spherical, measuring 167–168 mm long and 140–150 mm across. The eggshell is very thin, measuring from 0.5 to 0.7 mm thick.^[1] Like most other non-avian dinosaur eggs,^[3] Phaceloolithus's shell is stratified into two layers: the prismatic layer on the outside, and the mammillary layer on the inside.^[1] The mammillae are compressed into groups of two or three, and the pore canals are well-developed.^[1]

History

Phaceloolithus was first described as the sole species of the oofamily Phaceloolithidae in 1979 by Chinese paleontologists Zeng Demin and Zhang Jinjian, following its discovery in the Dongting basin of Hunan.^[1]

Parataxonomy

While Phaceloolithus has always been considered an oospecies of Phaceloolithidae, there is dispute about whether or not this oofamily is synonymous with the later-named Dendroolithidae. The oofamilies were first synonymized by Fang et al. in 2003.^[4] This position was supported by Ribeiro et al. in 2014,^[5] but other authors have considered the two oofamilies distinct,^[6]^[7] and in his master's thesis, Daniel Barta argued against synonymy because the brevity of the description of Phaceloolithidae makes any further referrals to that oofamily uncertain.^[8] If the synonymy is correct, then Phaceloolithus would be a sister taxon to Dendroolithus and Paradendroolithus. If not, then Phaceloolithus would be the sole oogenus of Phaceloolithus.^[9]

References

^ ^a ^b ^c ^d ^e ^f D. Zeng and J. Zhang. (1979). "On the dinosaurian eggs from the western Dongting Basin, Hunan". Vertebrata PalAsiatica 17(2):131–136
^ Carpenter, K. (1999). Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana.
^ Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray. (2012). "Fossil eggshell: Fragments from the past" UCMP's online fossil egg exhibit.
^ Fang, Xiao-si, et al. "Cretaceous fossil eggs from the Tiantai basin of Zhejiang, with a discussion on the extinction of dinosaurs." Geological Bulletin of China 22.7 (2003): 1–24.
^ Ribeiro, V., Mateus, O., Holwerda, F., Araújo, R., & Castanhinha, R. (2014). "Two new theropod egg sites from the Late Jurassic Lourinhã Formation, Portugal." Historical Biology, 26(2), 206–217.
^ Konstantin E. Mikhailov, Emily S. Bray & Karl E. Hirsch (1996). "Parataxonomy of fossil egg remains (Veterovata): basic principles and applications". Journal of Vertebrate Paleontology. 16 (4): 763–769. doi:10.1080/02724634.1996.10011364. JSTOR 4523773.
^ Barta, D. E., Brundridge, K. M., Croghan, J. A., Jackson, F. D., Varricchio, D. J., Jin, X., & Poust, A. W. (2014). "Eggs and clutches of the Spheroolithidae from the Cretaceous Tiantai basin, Zhejiang Province, China." Historical Biology, 26(2), 183–194.
^ Barta, D. E. (2014). "A phylogenetic approach to understanding dinosaur egg diversity and the evolution of reproductive traits within Dinosauria" (Master's thesis, Montana State University-Bozeman, College of Letters & Science).
^ Fang Xiao-si, Yue Zhao, Ling Hong. (2009). "近十五年来蛋化石研究概况 [Review of the Past 15 years’ Research on Fossil Eggs in China]". 地球学报, 30(4), 523–542.