Macroelongatoolithus is an oogenus of large, fossil theropod eggs (probably representing a giant caenagnathid). They are known from Asia and from North America.[1][2]
Fossil Macroelongatoolithus eggs have been found in the United States, China, and South Korea, ranging in age from Early Cretaceous to Maastrichtian.[2] More specifically, it is known in North America from the Cedar Mountain, Dakota, and Kelvin Formations of Utah,[3] the Wayan Formation of Idaho, the Blackleaf Formation of Montana, the Thomas Fork Formation of Wyoming,[2] and the Willow Tank Formation of Nevada.[4] In China, it is known from the Liangtoutang and Chichengshan Formations in Tiantai County, Zhejiang Province,[5][6] from the Gaogou, Sigou, Majiacun, and Zoumagang Formations in Henan Province, China.[2][7][8] It is known in South Korea from the Goseong Formation near Tongyeong and from Aphae-do in Shinan-gun, Jeollanam-do Province.[9][10]
Macrooelongatoolithus eggs are most notable for their large size. They are at least 34 centimetres (13 in) long, but the largest specimens are over 60 centimetres (24 in) long.[2] They are also very elongated, usually roughly three times longer than they are wide. They are often found in large clutches of up to 26 eggs, with the eggs forming a ring 2–3.3 metres (6.6–10.8 ft) in diameter. The shell is typically between 1.38 mm and 4.75 mm thick.[2][3]
Like other elongatoolithids, Macroelongatoolithus's eggshell is divided up into two structural layers, and the outer layer (called the continuous layer) is not divided up into distinct shell units, unlike other oofamilies. In Macroelongatoolithus, the boundary between the continuous layer and the mammillary layer (the inner layer of the eggshell, also called the cone layer) is wavy, but clearly defined. The ratio of the thickness of the two layers varies from 2:1 to 8:1.[2]
The surface ornamentation of the eggshells is variable, even on a single egg. It is usually lineartuberculate (nodes forming linear ridges), ramotuberculate (nodes forming irregular, meandering chains), or dispersituberculate (scattered nodes).[2]
Macroelongatoolithus specimens are extremely variable in size, shape, and microstructure, even in eggs laid by a single individual. For example, within a single clutch, the egg lengths can vary by several centimeters. The high amount of variability is probably due to their large size.[3]