First Mesozoic bird eggs from Korea, Onggwanoolithus
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Ben Creisler
Feb 20, 2026, 2:40:02 PM (10 hours ago) Feb 20
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Ben Creisler
Aphaedo is documented as a key mid-Cretaceous theropod egg locality in Korea.
Five distinct theropod-affinity ootaxa are identified from a single site.
A new avialan-type egg, Onggwanoolithus, is the first described from Korea.
Egg microstructure indicates ornithuromorph affinities, including crown birds.
Nesting patterns suggest paleoecological or preservational bias in egg assemblages.
Abstract
The Mesozoic record of the Korean Peninsula is remarkable in both the abundance and diversity of bird footprints, indicating that a wide range of taxa inhabited this region for an extended interval during the Cretaceous. In contrast, egg fossils attributable to Avialae have not previously been reported. Here, we report a new tiny theropod egg taxon, Onggwanoolithus aphaedoensis oogen. et oosp. Nov. based on multiple eggs from the mid-Cretaceous Ilseongsan Formation of Aphae Island (Aphaedo), which is described using micro-X-ray computed tomography and histological data. These eggs lack surface ornamentation and, in thin section, show three distinct layers, characteristics uniquely observed within Avialae, including in crown birds. Onggwanoolithus represents one of the earliest records of an egg showing these characteristics. Theropod egg miniaturization with concomitant shell thinning is first seen in the Late Jurassic, with very few Early or mid-Cretaceous records before becoming more abundant in the Late Cretaceous. We also describe the Aphaedo site, which preserves five ootaxa attributed to theropods, including Macroleongatoolithus, a second type of elongatoolithid, as well as dendroolithid, prismatoolithid eggs, and Onggwanoolithus. This theropod-dominated oofauna is unique among Korean Cretaceous egg sites and most closely resembles select theropod-rich egg assemblages reported from other parts of Asia and North America. Such assemblages may reflect nesting preferences and/or preservational biases. One of Aphaedo egg types is preserved in an intact nest structure and two others are known from largely intact eggs, suggesting limited or no transport of some eggs prior to deposition in overbank deposits of a floodplain environment.
A new paper:
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Onggwanoolithus aphaedoensis oogen. et oosp. nov.
Hyemin Jo, Jongyun Jung, Minguk Kim, Min Huh & Julia A. Clarke (2026)
Description of the first Mesozoic bird eggs from Korea and a new mid-cretaceous theropod-dominated egg locality
Palaeogeography, Palaeoclimatology, Palaeoecology 113653
doi: https://doi.org/10.1016/j.palaeo.2026.113653
https://www.sciencedirect.com/science/article/abs/pii/S0031018226001161
Highlights
Hyemin Jo, Jongyun Jung, Minguk Kim, Min Huh & Julia A. Clarke (2026)
Description of the first Mesozoic bird eggs from Korea and a new mid-cretaceous theropod-dominated egg locality
Palaeogeography, Palaeoclimatology, Palaeoecology 113653
doi: https://doi.org/10.1016/j.palaeo.2026.113653
https://www.sciencedirect.com/science/article/abs/pii/S0031018226001161
Highlights
Aphaedo is documented as a key mid-Cretaceous theropod egg locality in Korea.
Five distinct theropod-affinity ootaxa are identified from a single site.
A new avialan-type egg, Onggwanoolithus, is the first described from Korea.
Egg microstructure indicates ornithuromorph affinities, including crown birds.
Nesting patterns suggest paleoecological or preservational bias in egg assemblages.
Abstract
The Mesozoic record of the Korean Peninsula is remarkable in both the abundance and diversity of bird footprints, indicating that a wide range of taxa inhabited this region for an extended interval during the Cretaceous. In contrast, egg fossils attributable to Avialae have not previously been reported. Here, we report a new tiny theropod egg taxon, Onggwanoolithus aphaedoensis oogen. et oosp. Nov. based on multiple eggs from the mid-Cretaceous Ilseongsan Formation of Aphae Island (Aphaedo), which is described using micro-X-ray computed tomography and histological data. These eggs lack surface ornamentation and, in thin section, show three distinct layers, characteristics uniquely observed within Avialae, including in crown birds. Onggwanoolithus represents one of the earliest records of an egg showing these characteristics. Theropod egg miniaturization with concomitant shell thinning is first seen in the Late Jurassic, with very few Early or mid-Cretaceous records before becoming more abundant in the Late Cretaceous. We also describe the Aphaedo site, which preserves five ootaxa attributed to theropods, including Macroleongatoolithus, a second type of elongatoolithid, as well as dendroolithid, prismatoolithid eggs, and Onggwanoolithus. This theropod-dominated oofauna is unique among Korean Cretaceous egg sites and most closely resembles select theropod-rich egg assemblages reported from other parts of Asia and North America. Such assemblages may reflect nesting preferences and/or preservational biases. One of Aphaedo egg types is preserved in an intact nest structure and two others are known from largely intact eggs, suggesting limited or no transport of some eggs prior to deposition in overbank deposits of a floodplain environment.
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