Avimaia
Avimaia | |
---|---|
Fossil of Avimaia schweitzerae with an unlaid egg[1] | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | Avialae |
Clade: | †Enantiornithes |
Genus: | †Avimaia Bailleul et al. 2019[1] |
Type species | |
Avimaia schweitzerae[1] Bailleul et al. 2019[1]
|
Avimaia is a genus of
According to
Discovery and naming
In 2006, at
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]
Description
Avimaia is a relatively small member of the Enantiornithes.[1]
The describing authors found two distinguishing traits. They are
In several additional traits Avimaia differs from some relatives. The
Egg
Between the pubic bones of the fossil, a flattened egg is present, running from the last back vertebra to the front of the pygostyle, the fused outer tail vertebrae. It covers a surface of 5.2 cm2. It is the first time a fossil bird egg has been discovered within the abdomen of the female. The egg is not merely an outline of organic remains: the egg shells themselves have been preserved, which is again unique. The combined shells have a thickness of 0.2 to 0.4 millimetres.[1]
A section showed the presence of four to six separate shells stacked on top of each other, each about 0.05 millimetres thick. Each shell consists of three layers, as with modern birds and generally in derived dinosaur eggs. There is an inner mammillary layer, an intermediate prismatic layer and an outer crystalline layer. The three layers combined are rather thin: earlier reported shells of Enantiornithes are thicker. Another anomaly consists in the fact that the prismatic layer and outer layer combined are thinner than the mammillary layer, whereas normally the opposite is true. On the surface of the egg a brown organic layer is visible, which was identified as the cuticle. In the cuticle nanospheres of calcium phosphate were discovered, which are also present in the cuticle of some extant birds. Additionally, remains were identified of the egg membrane, the membrana testacea. The fibres of the membrane are individually visible and have a length of 1.5 to 4 micrometres. They possibly contain part of the original proteins. It is likely that during fossilisation, the egg shells shifted in relation to each other and were otherwise distorted.[1]
The presence of four to six shells on top of each other is difficult to explain. The authors considered the possibility that the shells represented two eggs, but this hypothesis was rejected. In case of two eggs, the two top shells should have mirrored each other, as they then should have been the opposite shells of a top egg. In reality, they mirror the lower shells. Furthermore, it is generally assumed that the
Medullary bone
In the thighbone, section showed that an inner layer of
Plumage
What little of the plumage has been preserved, seems to indicate that long tail feathers were absent. It has been suggested that in the Enantiornithes such long display feathers were limited to the males only, as an instance of
Phylogeny
Avimaia was placed in the Enantiornithes in 2019. A
Gallery
References
- ^ PMID 30894527.
- ^ EurekAlert!. Retrieved 20 March 2019.
- . Retrieved 20 March 2019.
- ^ a b Greshko, Michael (20 March 2019). "In a first, fossil bird found with unlaid egg - "I couldn't even sleep at night," the lead paleontologist says of her reaction to the discovery". National Geographic Society. Archived from the original on 20 March 2019. Retrieved 20 March 2019.
- ^ Gramling, Carolyn (20 March 2019). "In a first, a fossilized egg is found preserved inside an ancient bird - The offspring may have been the cause of its mother's demise, scientists suspect". Science News. Retrieved 20 March 2019.