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.

[5] The oospecific epiphets yaotunensis (Chinese: 窑屯 yáotún) and lashuyuanensis (Chinese: 腊树园 Làshùyuán) honor the localities where those oospecies were originally discovered (the Yaotun[5] and Lashuyuan[9] districts of Guangdong, respectively), affixing the Latin suffix -ensis to denote the place of origin;[13] the name mutabilis is Latin for changeable.

[3] Tanaka et al. (2015) found that among modern archosaurs (the group including birds, crocodilians, and dinosaurs), the porosity of eggshells can be used to accurately predict whether the eggs are buried or laid in open nests.

[19] 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.

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 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).

[14] Many Macroolithus specimens in South China have double- or multiple-layering of cones on the inner surface of the eggshell, a pathological condition known as ovum in ovo.

This pathology is correlated with a higher concentration of trace elements like Co, Cr, Cu, Mn, Ni, Pb, Sr, V, and Zn.

[20] Experiments on modern birds have demonstrated that exposure to high levels of these elements will cause them to be incorporated into the eggshell, but the precise mechanism behind the pathological multi-layering is unknown.

However, some paleontologists attribute the extinction event and the iridium anomaly to more gradual climatic change caused by the volcanic activity of the Deccan Traps.

Zhao et al. (2002 and 2009) have postulated that there were at least two iridium-delivering events over a time period consistent with the Deccan Traps volcanism, correlated with a gradual decline in diversity and eventual disappearance of fossil eggs from the Nanxiong Basin.

[21][22][23] However, Buck et al. (2004) disputed these claims, arguing that debris flows mixed and reworked the sediments near the boundary, causing a blurring of the iridium anomaly and the appearance of eggshell fragments on both sides.

[14] When Mikhailov described M. mutabilis, he found no microstructural difference in Zhao's original illustrations of M. rugustus and M. yaotunensis, but did not synonymize the oospecies because Chinese paleontologists considered them distinct.

[5] In 1991, the Russian paleontologist Konstantin Mikhailov introduced the modern classification of fossil eggs based on Zhao's parataxonomic naming system.

[2] In 2000, a fourth oospecies, "M." turolensis, was described by Spanish paleontologists Olga Amo-Sanjuán, José Ignacio Canudo, and Gloria Cuenca-Bescós based on material from Spain.

[15] In 2008, Chinese paleontologists Cheng Yen-nien, Ji Qiang, Wu Xiao-chun and Shan Hsi-yin discovered a pair of eggs representing the first in China to contain embryonic remains of oviraptorosaurs.

Mou 1992 noted the high gas conductance values in Macroolithus eggs and therefore concluded that they were laid in a very humid environment, buried underground or inside a mound.

They found, based on comparisons to modern eggs, that Macroolithus was predicted to be laid in open or partially covered nests.

[18] Wiemann et al. (2017) also criticized Mou and Deeming because they had only measured eggshell porosity at the middle section of the eggs and did not take into account the fact that the pore density is much lower near the poles.

[20][35] They postulated, contrary to the impact hypothesis, that the extinction was the result of a prolonged drought that increased the concentration of trace heavy metals, which adversely affected eggshell and embryo development of the dinosaurs causing the population to gradually decline and collapse.

[35] Zhao et al. revised this hypothesis in 2002, postulating a gradual extinction of Macroolithus caused by the volcanism of the Deccan Traps.

[21] In 2004, Buck et al. disputed this interpretation, arguing that the apparent gradual extinction was an illusion caused by reworking of sediments.

[1] In Henan, Macroolithus yaotunensis coexists with the other elongatoolithids Elongatoolithus andrewsi and E. elongatus, as well as Ovaloolithus and Paraspheroolithus of the Hugang, the Luyemiao, and the Sigou Formations.

[42] Well-preserved dinosaur remains are common in the Nemegt Formation,[43] including oviraptorosaurs,[42] titanosaurs,[44] troodontids, tyrannosaurs, ankylosaurs,[45] pachycephalosaurs,[46] hadrosaurs,[47] ornithomimosaurs, alvarezsaurs,[48] and therizinosaurs.

Compared to the Nemegt Formation, large dinosaurs are rare at Barun Goyot, where the fauna is dominated by protoceratopsids, oviraptorids, and ankylosaurids.

[51] Other types of fossil eggs from the Barun Goyot Formation include Protoceratopsidovum, Gobioolithus, Faveoloolithus, Dendroolithus, Spheroolithus, and Subtiliolithus.

[41] M. rugustus has also been found in the Manrak Formation (also called Manrakskaya Svita) of the Zaisan Basin in the East Kazakhstan Region.