An Early Cretaceous enantiornithine (Aves) preserving an unlaid egg and probable medullary bone

Alida M. Bailleul (), Jingmai O’Connor, Shukang Zhang, Zhiheng Li, Qiang Wang, Matthew C. Lamanna, Xufeng Zhu and Zhonghe Zhou
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Alida M. Bailleul: Institute of Vertebrate Paleontology and Paleoanthropology
Jingmai O’Connor: Institute of Vertebrate Paleontology and Paleoanthropology
Shukang Zhang: Institute of Vertebrate Paleontology and Paleoanthropology
Zhiheng Li: Institute of Vertebrate Paleontology and Paleoanthropology
Qiang Wang: Institute of Vertebrate Paleontology and Paleoanthropology
Matthew C. Lamanna: Carnegie Museum of Natural History
Xufeng Zhu: Institute of Vertebrate Paleontology and Paleoanthropology
Zhonghe Zhou: Institute of Vertebrate Paleontology and Paleoanthropology

Nature Communications, 2019, vol. 10, issue 1, 1-10

Abstract: Abstract Understanding non-crown dinosaur reproduction is hindered by a paucity of directly associated adults with reproductive traces. Here we describe a new enantiornithine, Avimaia schweitzerae gen. et sp. nov., from the Lower Cretaceous Xiagou Formation with an unlaid egg two-dimensionally preserved within the abdominothoracic cavity. Ground-sections reveal abnormal eggshell proportions, and multiple eggshell layers best interpreted as a multi-layered egg resulting from prolonged oviductal retention. Fragments of the shell membrane and cuticle are both preserved. SEM reveals that the cuticle consists of nanostructures resembling those found in neornithine eggs adapted for infection-prone environments, which are hypothesized to represent the ancestral avian condition. The femur preserves small amounts of probable medullary bone, a tissue found today only in reproductively active female birds. To our knowledge, no other occurrence of Mesozoic medullary bone is associated with indications of reproductive activity, such as a preserved egg, making our identification unique, and strongly supported.

Date: 2019
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DOI: 10.1038/s41467-019-09259-x

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