Shokawa cranial elements and new records of choristoderes from Lower Cretaceous of Japan
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Ben Creisler
Dec 7, 2025, 8:57:04 PM12/7/25
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Ben Creisler
A new paper:
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Ryoko Matsumoto, Makoto Manabe & Susan E. Evans (2025)
Cranial elements of Shokawa ikoi, and new records of choristoderes from the Lower Cretaceous Okurodani Formation, Tetori Group, Japan.
Cretaceous Research 106283
doi: https://doi.org/10.1016/j.cretres.2025.106283
https://www.sciencedirect.com/science/article/abs/pii/S019566712500206X
The extinct reptilian group Choristodera has been recorded from the Lower Cretaceous Tetori Group of Japan. Within the Tetori Group, the Okurodani Formation was the first deposit to yield choristoderan remains with the discovery of the postcranial skeleton of the long-necked Shokawa ikoi. However, until now, the formation has yielded only limited choristoderan material. Here, we report on several further choristodere remains, including the finding of an unexposed skull element during a μCT examination of the holotype of Shokawa ikoi. Although the new specimens are all isolated elements, detailed comparison has revealed that they represent an unexpected diversity of taxa including a long-snouted neochoristodere, a non-neochoristodere with an open lower temporal fenestra, and a possible new monjurosuchid. Similarities between the choristoderan assemblages of the Jehol Biota of China and the Tetori Group of Japan have previously been recognised. However, the new choristoderan records from the Okurodani Formation albeit fragmentary, suggest possible differences in assemblage composition, and add to our knowledge of choristoderan diversity in eastern Asia at a key stage in their evolutionary history.
Ryoko Matsumoto, Makoto Manabe & Susan E. Evans (2025)
Cranial elements of Shokawa ikoi, and new records of choristoderes from the Lower Cretaceous Okurodani Formation, Tetori Group, Japan.
Cretaceous Research 106283
doi: https://doi.org/10.1016/j.cretres.2025.106283
https://www.sciencedirect.com/science/article/abs/pii/S019566712500206X
The extinct reptilian group Choristodera has been recorded from the Lower Cretaceous Tetori Group of Japan. Within the Tetori Group, the Okurodani Formation was the first deposit to yield choristoderan remains with the discovery of the postcranial skeleton of the long-necked Shokawa ikoi. However, until now, the formation has yielded only limited choristoderan material. Here, we report on several further choristodere remains, including the finding of an unexposed skull element during a μCT examination of the holotype of Shokawa ikoi. Although the new specimens are all isolated elements, detailed comparison has revealed that they represent an unexpected diversity of taxa including a long-snouted neochoristodere, a non-neochoristodere with an open lower temporal fenestra, and a possible new monjurosuchid. Similarities between the choristoderan assemblages of the Jehol Biota of China and the Tetori Group of Japan have previously been recognised. However, the new choristoderan records from the Okurodani Formation albeit fragmentary, suggest possible differences in assemblage composition, and add to our knowledge of choristoderan diversity in eastern Asia at a key stage in their evolutionary history.
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