Fossil eggshells from the Early Cretaceous Okurodani Formation, northern central Japan

Seven isolated eggshell fragments and six eggshell impressions were collected from the Okurodani Formation (Hauterivian to Barremian) in Shokawa, Takayama City, Gifu Prefecture, Japan. To date, these specimens represent the oldest fossil eggshells in the country. Microscopic observations classified...

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Bibliographic Details
Published in:Historical biology 2023-12, Vol.35 (12), p.2396-2407
Main Authors: Uematsu, Rina, Tanaka, Kohei, Kozu, Shohei, Isaji, Shinji, Shimojima, Shizuo
Format: Article
Language:English
Subjects:
Cretaceous
Early Cretaceous
Egg shells
Eggshells
Fragments
Japan
Microstructure
Okurodani Formation
Phylogeny
Prismatoolithidae
Range extension
Testudoolithidae
Turtles
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Summary:Seven isolated eggshell fragments and six eggshell impressions were collected from the Okurodani Formation (Hauterivian to Barremian) in Shokawa, Takayama City, Gifu Prefecture, Japan. To date, these specimens represent the oldest fossil eggshells in the country. Microscopic observations classified the eggshells into Testudoolithidae indet., Ramoprismatoolithus okurai oogen. et oosp. nov. and indeterminate type. For Testudoolithidae indet., the eggshell microstructure and estimated egg size suggest that they could be laid by any of the cryptodiran turtles reported by skeletal remains from the formation: Trionychoidea, Xinjiangchelyidae and Sinemydidae. Ramoprismatoolithus okurai bears prismatic microstructure and ramifying ridges on the outer surface, the combination of which is unusual for prismatoolithid eggshells. Based on morphological observations and phylogenetic analyses, Ramoprismatoolithus was ascribed to troodontid or closely related non-avian maniraptorans. The remaining specimens consist of eggshell surface impressions without original fragments, for which oospecies and taxonomic affinity are indeterminate. These findings demonstrate that eggshell fragments shed light on small-bodied taxa that are poorly represented by skeletal remains in the region. While the fossil record of small maniraptoran species from the early Early Cretaceous is relatively scarce worldwide, Ramoprismatoolithus adds to this record and extends the confirmed geographic range of this clade. http://www.zoobank.org/urn:lsid:zoobank.org:act:E023F0B5-59F3-47DD-B804-345A92750BEF
ISSN:0891-2963
1029-2381
DOI:10.1080/08912963.2022.2142910