Dictyoolithus

Dictyoolithus is an oogenus of dinosaur egg from the Cretaceous of China. It is notable for having over five superimposed layers of eggshell units. Possibly, it was laid by megalosauroid dinosaurs.

Dictyoolithus
Temporal range: Cretaceous
Egg fossil classification
Basic shell type: †Dinosauroid-spherulitic
Oofamily: †Dictyoolithidae
Oogenus: †Dictyoolithus
Zhao, 1994
Type oospecies
†Dictyoolithus hongpoensis
Zhao, 1994

Distribution

Dictyoolithus is known from Hongpo, a town in Xixia County, Henan. This is in the Lower Cretaceous Sigou Formation.[1] It has also been discovered in Lishui, Zhejiang, in the Upper Cretaceous Chichengshan Formation.[2]

History

Dictyoolithus was first discovered and described in 1994 by Chinese paleontologist and pioneer of fossil eggshell classification, Zhao Zikui. He named two oopsecies: D. hongpoensis and D. neixiangensis (now Protodictyoolithus neixiangensis). However, since excavations were still going on at the time, his description was brief.[1] In 2004, a third oospecies was named, D. jiangi,[3] followed by a fourth, D. gonzhulingensis in 2006.[4] However, in 2013 Chinese paleontologists Wang Qiang, Zhao Zikui, Wang Xiaolin, Zhang Shukang, and Jiang Yan'gen did a reanalysis of the entire oofamily Dictyoolithidae, and split the oogenus Dictyoolithus into two, classifying "D." neixiangensis and "D." jiangi within a new oogenus: Protodictyoolithus. Furthermore, they moved "D." gonzhulingensis into an entirely different oofamily and oogenus, reclassifying it as a member of Similifaveoloolithus.[5]

Description

Dictyoolithus eggs are roughly spherical and measure from 12–16 centimetres (4.7–6.3 in) in diameter.[2] Their eggshell is between 2.5 and 2.8 mm thick. The surface ornamentation is smooth with a grainy texture, or has very low rounded nodes. The eggshell is notable for being composed of more than five superimposed layers of eggshell units.[5] In some specimens, found at Lishui, no superimposed layers of eggshells were found.[2] However, it is not certain that these specimens in fact represent Dictyoolithus.[5] The eggshell units have a reticulate organization.[1]

Paleobiology

Since no embryos or adult remains have been found with Dictyoolithus eggs, it is uncertain what kind of dinosaur laid them.[6] A cladistic analysis in 2010 by Jin et al. found Dictyoolithus to be basal theropod eggs.[2] Similarly, Sellés and Galobart in 2015 found Dictyoolithus to be basal theropods, and considered it to be the eggs of megalosauroids.[7]

Unlike many dinosaur eggs, the calcareous and membranous parts of Dictyoolithus eggshells probably formed simultaneously in the oviduct, as in the modern tuatara.[1]

Parataxonomy

Dictyoolithus is classified in the oofamily Dictyoolithidae, alongside Protodictyoolithus and Paradictyoolithus. It contains only a single oospecies: D. hongpoensis.[5] Mikhailov (1997) suggested that it may actually be a dendroolithid.[8]

References
  1. Z.-K. Zhao. (1994) "Dinosaur eggs in China:On the structure and evolution of eggshells." In K. Carpenter, K. F. Hirsch, and J. R. Horner (eds.), Dinosaur Eggs and Babies, Cambridge University Press, Cambridge. Cambridge. pp. 184–203.
  2. Jin X.S., Jackson F.D., Varricchio D.J., Y. Azuma, and He T. (2010) "The first Dictyoolithus egg clutches from the Lishui Basin, Zhejiang Province, China." Journal of Vertebrate Paleontology, 30(1): 188–195
  3. Liu, J., & Zhao, Z. (2004). A new oospecies of the dinosaur eggs (Dictyoolithus) from Laiyang, Shandong Province. Vertebrata Pal Asiatica, 42(2), 166–170.
  4. Wang Qiang, Zan Shu-Qin, Jin Li-Yong, Chen Jun (2006). A New Oospecies, Dictyoolithus Gongzhulingensis, from the Early Cretaceous Quantou Formation in the Central Jilin Province. Journal of Jilin University (Earth Science Edition), 36(2): 153–157.
  5. Wang Qiang, Zhao Zikui, Wang Xiaolin, Zhang Shukang, and Jiang Yan'gen. (2013) "New forms of dictyoolithids from the Tiantai Basin, Zhejiang Province of China and a parataxonomic revision of the dictyoolithids." Vertebrata PalAsiatica 51:43–54.
  6. Varricchio, D. J. (2011). A distinct dinosaur life history?. Historical Biology, 23(01), 91–107. Chicago
  7. Sellés, A. G., & Galobart, À. (2015). "Reassessing the endemic European Upper Cretaceous dinosaur egg Cairanoolithus." Historical Biology, (ahead-of-print), 1–14.
  8. Mikhailov, Konstantin (1997). "Fossil and recent eggshell in amniotic vertebrates: fine structure, comparative morphology, and classification". Special Papers in Palaeontology. London: The Palaeontological Association. 56: 1–77.
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