Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan
Graphical abstract
Introduction
Early Cretaceous fossil sites that preserve a diverse assemblage of small theropod dinosaurs are rare in East Asia. One notable exception is the localities of the Jehol Biota in northeastern China that have produced a high diversity of well-preserved skeletons of small avian and non-avian theropods (Zhou et al., 2003, Zhou and Wang, 2010). Small theropod diversity at other Early Cretaceous localities in East Asia is poorly understood, likely due in part to the generally low preservation potential of small skeletons (Brown et al., 2013). When skeletal remains are scarce, fossil eggshells can be useful to understand faunal taxonomic composition and diversity (Tanaka et al., 2016, Zelenitsky et al., 2017a, Zelenitsky et al., 2017b). Fossil egg localities of the Shiwha Basin in South Korea (Lee, 2003) and of the Kamitaki locality in southwestern Japan (Tanaka et al., 2016) both hint at a diversity of small theropods, otherwise poorly known from skeletal remains in these areas during the Early Cretaceous.
The Early Cretaceous (Albian) Kamitaki Locality in the eastern Hyogo Prefecture of Japan has yielded numerous fossil eggshells and bones that indicate a large diversity of dinosaurs in the region (Saegusa and Ikeda, 2014, Tanaka et al., 2016). The diversity of small theropods was shown to be relatively high based on the presence of eggshell remains of at least four distinct ootaxa (i.e., Elongatoolithus, Nipponoolithus, and two species of prismatoolithid: Tanaka et al., 2016), for which skeletal remains are poor or lacking at the site (Saegusa and Ikeda, 2014). Although previous discoveries at the Kamitaki Locality were limited to isolated eggshell fragments, here we report on newly discovered partial to nearly complete eggs and eggshell fragments from new nesting horizons that provide evidence for additional small theropod species in the region.
Section snippets
Geologic setting
The Kamitaki Locality is located in the upper part of the Ohyamashimo Formation (formerly known as the ‘Lower Formation’) of the Sasayama Group (Fig. 1: Hayashi et al., 2017). The upper part of this formation is composed mainly of mudstones, sandstones, and conglomerates, sediments that were deposited in fluvial environments under a semi-arid to subhumid climate (Hayashi et al., 2017). Radiometric dating of tuff beds in the lower part of the Ohyamashimo Formation and in the overlying Sawada
Material and methods
Egg remains at the Kamitaki Egg Quarry were first discovered in 2015 and the quarry was intensively excavated in the Winter of 2019. An area of approximately 24 m2 was mapped (Fig. 2) and aerial photographs were taken with the use of a drone (DJI Mavic Air). Eggs, eggshell fragments, as well as small bones and tooth remains of anurans, lizards, and dinosaurs were collected throughout the mudstone layer. High concentrations of eggs/eggshells were found at two horizons located approximately 30 cm
Systematic paleontology
Oofamily. Incertae sedis.
Oogenus. Himeoolithus oogen. nov.
ZOOBANK ID: urn:lsid:zoobank.org:act:49AE6ABE-5E4D-4992-A5FC-5C13562A1213
Type oospecies. Himeoolithus murakamii oosp. nov., by present designation.
Diagnosis. As for the type and only oospecies.
Etymology. ‘hime’ meaning small, little, or pretty in Japanese, referring to the exceptionally small size of the egg, ‘oo’ meaning egg, and ‘lithos’ meaning stone in Greek. The generic name is masculine in gender.
Type locality and horizon. As for
Phylogenetic analyses
In order to determine the phylogenetic position of the ootaxa from the Kamitaki Egg Quarry (i.e., Himeoolithus murakamii, Nipponoolithus ramosus, and Subtiliolithus hyogoensis), three cladistic analyses using the oological data matrices of Zelenitsky, 2004, Zelenitsky and Therrien, 2008b, and Jin et al. (2010) were conducted with the software TNT v.1.5 (Goloboff and Catalano, 2016). These original data matrices were altered in subsequent studies by the addition/modification of ootaxa and/or
Discussion
At least six eggshell morphotypes or ootaxa are recognized from the Kamitaki Locality of the Albian Ohyamashimo Formation of southwestern Japan (Fig. 1), making it one of the most taxonomically diverse Early Cretaceous egg localities known (Fig. 8). The locality has produced both skeletal remains and eggshells from the Kamitaki Bonebed Quarry (Saegusa and Ikeda, 2014, Tanaka et al., 2016), as well as the eggs and eggshells described here from the nearby, but slightly stratigraphically higher,
Conclusions
New egg horizons (Kamitaki Egg Quarry), situated 5.50–6.75 m higher than the previously-known eggshell horizons (Kamitaki Bonebed Quarry), at the Lower Cretaceous Kamitaki Locality in the Hyogo Prefecture provide additional information regarding the diversity of theropod dinosaurs in the region. Four theropod ootaxa were identified from the new egg horizons: Himeoolithus murakamii oogen. et oosp. nov., Subtiliolithus hyogoensis oosp. nov., Nipponoolithus ramosus and Prismatoolithus sp.,
CRediT authorship contribution statement
Kohei Tanaka: Methodology, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Darla K. Zelenitsky: Writing - original draft, Writing - review & editing. François Therrien: Writing - original draft, Writing - review & editing. Tadahiro Ikeda: Data curation, Formal analysis, Writing - review & editing. Katsuhiro Kubota: Data curation, Formal analysis, Writing - review & editing. Haruo Saegusa: Data curation, Formal analysis, Writing - review & editing. Tomonori
Acknowledgements
We thank the Self-Government Council of Kamikuge, staffs and volunteers at the Museum of Nature and Human Activities, Hyogo, as well as Tamba City and Matsutaka Kogyo Co., Ltd., for their significant effort on the excavation and preparation for the specimens. We also thank Kumiko Handa, Kosuke Nakamura, Hidehiko Nomura, Natsuko Takagi, Chisako Sakata, Makoto Manabe, Mariela Fernández, and Miguel Moreno-Azanza for their support. The manuscript was improved by editor Eduardo Koutsoukos and the
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2023, Journal of PalaeogeographyA fossil Monstersauria (Squamata: Anguimorpha) from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan
2022, Cretaceous ResearchCitation Excerpt :To date, abundant terrestrial vertebrate and invertebrate fossils, such as dinosaurs (e.g., Tambatitanis amicitiae), mammals (e.g., Sasayamamylos kawaii), lizards (e.g., Pachygenys adachii), anurans (e.g., Hyogobatrachus wadai), ostracods (e.g., Mongolocypris sp.), bivalves (e.g., Sphaerium coreanicum), gastropods (Viviparus sp. cf. keishoensis), and estherids, have been found at the four localities (Kamitaki in Tamba City, and Ohyamashimo [“Oyama” in Ikeda et al., 2015], Miyada, and Nishikosa in TambaSasayama City: Fig. 1) of the formation (e.g., Kusuhashi et al., 2013; Saegusa and Ikeda, 2014; Ikeda et al., 2015, 2016; Tanaka et al., 2016; Hayashi et al., 2017). With more than 1300 egg and eggshell specimens (Tanaka et al., 2020), and fragmentary vertebrate remains, the new lizard material described here was excavated from the red-brown mudstone layer of the Kamitaki Egg Quarry at the Kamitaki Locality, which is equivalent to the upper part of the Ohyamashimo Formation of the Sasayama Group (Fig. 1) (see Tanaka et al., [2020] for details of the layer). Several authors have investigated the geological ages of the formations of the Sasayama Group (e.g., Matsuura and Yoshikawa, 1992; Yoshikawa, 1993; Hayashi et al., 2010).
Fossil eggshells of amniotes as a paleothermometry tool
2021, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :Considering that both Korea and Japan were characterized by heavy volcanism/magmatism in the Cretaceous (Fig. 1; Taira, 2001; Chough and Sohn, 2010), the dark color of fossil eggshells from both countries might have been caused by the combination of local volcanism, magmatism, and/or burial depth. Indeed, egg fossil localities in Korea and Japan are frequently characterized by the presence of volcanic rocks (Azuma, 2003; Lee, 2003; Paik et al., 2004, 2012; Imai and Azuma, 2015; Gihm et al., 2017; Tanaka et al., 2020; Imai et al., 2020) and Kim et al. (2009) suggested that thermal activity (e.g. volcanism and plutonism) of the one of fossil localities of Korea might have influenced the δ18O values of fossil eggs. Similarly, the Two Medicine and Frontier formations in Montana, USA, were influenced by volcanism (Dyman et al., 2008; Foreman et al., 2008), and eggshell from these formations are as dark as Korean and Japanese eggshells (SC, personal observation).