Avimaia
Avimaia is a genus of fossil birds of the Enantiornithes clade[2] that lived about 115 million years ago in Northwest China.[1] The only known species is A. schweitzerae.[1] The holotype fossil of the bird was found in the Xiagou Formation, and is noted as the first discovered fossil bird with an unlaid egg.[1][3][4] Abnormalities, including egg binding in which the egg becomes stuck within the body of the bird causing death, were found in the egg suggesting that the preserved egg may have caused this bird's demise. Egg binding is a serious and lethal condition that is fairly common in small birds undergoing stress.[2][5]
According to paleontologist Jasmina Wiemann of Yale University, “This is a spectacular fossil with a lot of potential for future paleobiological investigations."[4] Further, "This new specimen is arguably one of the most interesting Cretaceous fossil birds yet discovered, providing more reproductive information than any other Mesozoic fossil bird," according to a paleontology researcher at the Chinese Academy of Sciences.[2]
In 2006, at Changma in Gansu the skeleton was found of an enantiornithean bird. In several studies it was referred to with its field number DCAGS-IG-06-CM-012 or FDRC-06-CM-012.[1]
In 2019, the type species Avimaia schweitzerae was named and described by Alida M. Bailleul, Jingmai Kathleen O’Connor, Zhang Shukang, Li Zhiheng, Wang Qiang, Matthew C. Lamanna, Zhu Xufeng and Zhou Zhonghe. The generic name is a combination of the Latin avis, "bird", and Maia, a mother goddess, in reference to the find of an egg in the abdomen of the fossil. The specific name honours Mary Higby Schweitzer, one of the founders of the application of molecular biology in paleontology.[1]
The holotype, IVPP V25371, was found in a layer of the lower-middle Xiagou Formation. It consists of a partial skeleton lacking the skull, compressed on a single plate. It conserves the rear half of the body. It is articulated and visible from the underside. Parts of the plumage and an egg are preserved. A second specimen, CAGS-IG-04-CM-007, was referred to the species. It is a partial skeleton lacking the skull. It is not articulated and preserves parts of the pelvis and the hindlimbs.[1]
The describing authors found two distinguishing traits. They are autapomorphies, unique derived characters. The pubic bone has a slender build and is curved upwards, causing a hollow profile over the entire length of its rear edge. The rear end of the ischium is curved to above.[1]
