page_title: Oviraptoridae
section_title: Reproduction
hierarchical_section_title: Oviraptoridae / Paleobiology / Reproduction
caption_attribution_description: English: Life restoration of Heyuannia with its nest of eggs
context_page_description: Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between one and two metres long in most cases, though some possible oviraptorids were enormous. Oviraptorids are currently known only from the Late Cretaceous of Asia, with the most well-known species and complete specimens found only in the Gobi Desert of Mongolia and northwestern China.
context_section_description: Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of Oviraptor philoceratops, Citipati osmolskae, Nemegtomaia and cf. Machairasaurus have been found in brooding positions in association with nests. All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.
  Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.
  The first oviraptorid eggs (of the genus Oviraptor, which mean "Egg thief") were found in close proximity to the remains of the ceratopsian dinosaur Protoceratops and it was assumed that the oviraptorids were preying upon the eggs of the ceratopsians. It was not until 1993, when a Citipati embryo was discovered inside an egg of the type assigned to Protoceratops, that the error was corrected. Norell et al., who recognized the embryo as oviraptorid, assigned it to the genus Citipati. The egg containing the embryo was smaller than most known Citipati eggs at only 12 cm, though it was partially eroded and broken into three pieces, making an accurate estimate of its original size difficult. The embryo-bearing egg was otherwise identical to other oviraptorid eggs in shell structure and was found in an isolated nest, again arranged in a circular pattern.
   
  An oviraptorosaurian specimen from China described in 2005 was found to have two unlaid eggs within the pelvic canal. This suggests that, unlike modern crocodilians, oviraptorosaurs did not produce and lay many eggs at the same time. Rather, the eggs were produced within the reproductive organs in pairs, and laid two at a time, with the mother positioned in the center of the nest and rotating in a circle as each pair was laid. This behavior is supported by the fact that the eggs oval shape, with the more narrow end pointing backward from the birth canal, matching their orientation toward the center of the nest after being laid.
  The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds. Like crocodilians, they had two oviducts.  However, crocodilians produce multiple shelled eggs per oviduct at a time, whereas oviraptorosaurs, like birds, produced only one egg per oviduct at a time.
  In 2017, paleontologists discovered colored pigments in some fossilized oviraptorid embryos of the egg-shell genus Macroolithus (which may represent eggs of Heyuannia). Examinations of eggs attributed to Heyuannia by Jasmina Wiemann and Tzu-Ruei Yang et al revealed the eggs preserved the blue-green pigment biliverdin and the reddish-brown pigment protoporphyrin, the same pigments found in many modern birds' eggshells. The eggs are thought to have been a blue-green color, because biliverdin is preserved in much greater abundance the photoporphyrin. In modern bird eggs, coloration can camouflage the eggs or help parents identify eggs, and it is correlated with more intensive parental care.
caption: Heyuannia restoration with nest
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