Sasayamagnomus Explained

Sasayamagnomus (meaning "Gnome from Sasayama") is a genus of neoceratopsian dinosaur from the Early Cretaceous (Albian) Ohyamashimo Formation of Hyogo prefecture, Japan. The genus contains a single species, S. saegusai.[1] Type specimen is estimated to reach 80cm (30inches) long, although this specimen is not fully grown.[2]

Discovery and naming

Sasayamagnomus was found at the Miyada microvertebrate site in Tamba-Sasayama city, Hyogo Prefecture. It is known from 17 assorted cranial bones, the right coracoid and a left tibia. The presence of two right nasals in the material suggests that at least two individuals were represented. Before its formal description, it had been announced in a conference abstract in 2023.[3]

The holotype is specimen MNHAH D1-060516, and it was formally described as a new genus and species of neoceratopsian in 2024. The generic name Sasayamagnomus is named after the Sasayama Basin, from where the bones were collected, and the Latin word for gnome, gnomus. The specific name saegusai honors the late Dr. Haruo Saegusa, who was the leader in dinosaur excavation in the Tamba area, and was a significant contributor to vertebrate paleontology in the Hyogo Prefecture.

Classification

In their phylogenetic analyses, Tanaka et al. (2024) recovered Sasayamagnomus as the sister taxon to Aquilops in a basal neoceratopsian clade also containing Auroraceratops. Their results are displayed in the cladogram below:

Paleoecology

Sasayamagnomus is known from the Ohyamashimo Formation (Sasayama Group), which dates to the early–middle Albian age from the end of the Early Cretaceous.[4] These layers are predominantly made up by sandstones, mudstones, and conglomerates. The depositional environment represents a fluvial system with a subhumid to semi-arid climate.[5] Dinosaur teeth are common in various localities throughout this formation including those belonging to other theropods (dromaeosaurids, therizinosaurs, and tyrannosauroids) as well as sauropods, ankylosaurs, and iguanodontians.[6] Several dinosaurian oospecies (egg fossils) have also described, including Himeoolithus, Subtiliolithus, Nipponoolithus, and Prismatoolithus.[7] The monstersaurian lizard Morohasaurus, the titanosauriform sauropod Tambatitanis, and the troodontid theropod Hypnovenator are also known from the formation.[8] [9] Although not specified as this Formation in original descriptions, Sasayama Group have some other fossil fauna known, such as eutherian Sasayamamylos,[10] scincomorph Pachygenys,[11] two frogs Hyogobatrachus and Tambabatrachus.[12]

See also

Notes and References

  1. Tanaka . Tomonori . Chiba . Kentaro . Ikeda . Tadahiro . Ryan . Michael J. . A new neoceratopsian (Ornithischia, Ceratopsia) from the Lower Cretaceous Ohyamashimo Formation (Albian), southwestern Japan . Papers in Palaeontology . September 2024 . 10 . 5 . 10.1002/spp2.1587.
  2. Web site: 兵庫県で発見の角竜類の化石 新属新種と確認 お知らせ・トピックス . 2024-09-04 . 岡山理科大学 . ja.
  3. Tanaka . Tomonori . Chiba . Kentaro . Ikeda . Tadahiro . Kubota . Katsuhiro . 2023 . Phylogenetic position of a ceratopsian dinosaur from the Lower Cretaceous Ohyamashimo Formation (Albian) of the Sasayama Group in Tambasasayama City, Hyogo, Japan . The Palaeontological Society of Japan.
  4. Kubota . K. . Kobayashi . Y. . Ikeda . T. . Early Cretaceous troodontine troodontid (Dinosauria: Theropoda) from the Ohyamashimo Formation of Japan reveals the early evolution of Troodontinae . 2024 . Scientific Reports . 14 . 16392 . 10.1038/s41598-024-66815-2 . free . 11272788 .
  5. Hayashi . Keiichi . Fujita . Saki . Koarai . Kazuto . Matsukawa . Masaki . 2017-09-15 . Stratigraphy and paleoenvironment of the Cretaceous Sasayama Group in the Sasayama area, Hyogo Prefecture, western Japan . The Journal of the Geological Society of Japan . en . 123 . 9 . 747–764 . 10.5575/geosoc.2017.0016 . 0016-7630. free .
  6. Kubota . Katsuhiro . 日本産の中生代恐竜化石目録 2022年版 . A list of Mesozoic dinosaur fossils from Japan in 2022 . Bulletin of the Gunma Museum of Natural History . 27 . 157–170.
  7. Tanaka . Kohei . Zelenitsky . Darla K. . Therrien . François . Ikeda . Tadahiro . Kubota . Katsuhiro . Saegusa . Haruo . Tanaka . Tomonori . Ikuno . Kenji . 2020 . Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan . . 114 . Article 104519 . 10.1016/j.cretres.2020.104519 . 2020CrRes.11404519T . 219449961 .
  8. Ikeda . T. . Ota . H. . Tanaka . T. . Ikuno . K. . Kubota . K. . Tanaka . K. . Saegusa . H. . 2021 . A fossil Monstersauria (Squamata: Anguimorpha) from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan . . 130 . Article 105063 . 10.1016/j.cretres.2021.105063 . 239230916 . free .
  9. Saegusa, H. . Ikeda, T. . 2014 . A new titanosauriform sauropod (Dinosauria: Saurischia) from the Lower Cretaceous of Hyogo, Japan . Zootaxa . 3848 . 1 . 1–66 . 10.11646/zootaxa.3848.1.1 . 25112425. free .
  10. Kusuhashi . Nao . Tsutsumi . Yukiyasu . Saegusa . Haruo . Horie . Kenji . Ikeda . Tadahiro . Yokoyama . Kazumi . Shiraishi . Kazuyuki . 2013-05-22 . A new Early Cretaceous eutherian mammal from the Sasayama Group, Hyogo, Japan . Proceedings of the Royal Society B: Biological Sciences . en . 280 . 1759 . 20130142 . 10.1098/rspb.2013.0142 . 0962-8452 . 3619506 . 23536594.
  11. Ikeda . Tadahiro . Ota . Hidetoshi . Saegusa . Haruo . 2015-01-02 . A new fossil lizard from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, western Honshu, Japan . Journal of Vertebrate Paleontology . en . 35 . 1 . e885032 . 10.1080/02724634.2014.885032 . 0272-4634.
  12. Ikeda . Tadahiro . Ota . Hidetoshi . Matsui . Masafumi . 2016-06-01 . New fossil anurans from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, Western Honshu, Japan . Cretaceous Research . 61 . 108–123 . 10.1016/j.cretres.2015.12.024 . 0195-6671.

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