page_title: Macroolithus
section_title: Embryos
hierarchical_section_title: Macroolithus / Paleobiology and parenting / Embryos
caption_attribution_description: English: Life restoration of Heyuannia with its nest of eggs
context_page_description: Macroolithus is an oogenus of dinosaur egg belonging to the oofamily Elongatoolithidae. The type oospecies, M. rugustus, was originally described under the now-defunct oogenus name Oolithes. Three other oospecies are known: M. yaotunensis, M. mutabilis, and M. lashuyuanensis. They are relatively large, elongated eggs with a two-layered eggshell. Their nests consist of large, concentric rings of paired eggs. There is evidence of blue-green pigmentation in its shell, which may have helped camouflage the nests.
  Macroolithus eggs have been found containing oviraptorid dinosaur embryos resembling Heyuannia. Multiple other associations between oviraptorid and elongatoolithids confirm that the parent of Macroolithus was an oviraptorid.
  It is found in Upper Cretaceous formations of central and eastern Asia; fossils have been found in Mongolia, Kazakhstan and China. In the Nanxiong formation in Southern China, Macroolithus fossils range up to and possibly over the Cretaceous-Tertiary boundary, which is traditionally assumed to mark the extinction of the non-avian dinosaurs.
context_section_description: A few Macroolithus eggs preserve embryonic remains of oviraptorids inside. Two eggs containing embryos found in the Upper Cretaceous Nanxiong Formation near Ganzhou, Jiangxi were referred to M. yaotunensis in 2008. One of these embryos shows a much greater degree of bone development (ossification) than the other; it preserves ossified hind limbs and several vertebrae. The fact that the cervical vertebrae not only have ossified centra and neural arches, but also have ossified zygapophyses, led Cheng et al. to conclude that this embryo may in fact represent a hatchling, since in modern chickens and skuas these zygaphyses are cartilaginous until hatching. Also, the embryo's foot anatomy (specifically, the proportions of its metatarsals) resembles that of the oviraptorid Heyuannia huangi, indicating that these eggs belong to H. huangi or a similar species. The other egg has a much less developed embryo, with only the hind limbs preserved. While this does not permit comparison on the species level, the tibia (shinbone) confirms that it is an oviraptorosaur.
  Three more eggs containing embryos from the same formation were described in 2016 by Wang et al. Though they noted that these eggs strongly resemble M. yaotunensis, they declined to refer them to any ootaxon lower than Elongatoolithidae because Macroolithus is not clearly defined and is in need of revision. The embryos within these eggs are some of the most well-preserved of any oviraptorids, providing new information on oviraptorid ontogeny. The specimens show a relatively shallow head which indicates that as oviraptorids matured, their skulls grew dorsoventrally (top-to-bottom) faster than anteroposteriorly (front-to-back). This growth pattern is unusual among theropods, but is also seen in derived ("advanced") tyrannosaurids. Also unusual is that, even at this early stage of development, the nasal bones are fused. Coincidentally, tyrannosaurids also show fusion of the nasals early in development.
caption: Artist's restoration of Heyuannia with its nest
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