Open Paleo

Koshisaurus

Shibata & Azuma, 2015 koh-shee-SOR-us

Named for 'Koshi', an old Japanese regional name for the area including Fukui Prefecture where the fossils were discovered, combined with Greek 'sauros' meaning 'lizard'.

121.4–113.2 million years ago Aptian, Early Cretaceous
Early Cretaceous stages

Koshisaurus is a monospecific genus of basal hadrosauroid from the Kitadani Formation in Japan. The discovery of the genus suggests that hadrosauroids had higher diversity along the eastern margin of Asia in the Early Cretaceous. "Koshi" means an old Japanese regional name including Fukui prefecture where fossils of the genus were discovered.

Under dispute

Koshisaurus katsuyama was recovered at the base of Hadrosauroidea by its describers (Shibata and Azuma, 2015) and among Eurasian hadrosauroids by Madzia and colleagues (2019), but Tsogtbaatar and colleagues (2019) recovered it as the sister to Hadrosauriformes, outside Hadrosauroidea.

Diagnosis

  1. Lingual ridge running apicobasally on the maxillary tooth crown, the genus's sole autapomorphy (the labial primary and subsidiary ridges are common to hadrosauriforms)
  2. Antorbital fossa positioned between the main and secondary lacrimal processes
  3. Rostroventral process of the maxilla curving rostroventrally
  4. Maxillary tooth row nearly straight in occlusal view
  5. Enclosed obturator foramen of the pubis
  6. U-shaped extensor intercondylar groove of the femur, partially enclosed by expansion of the medial and lateral condyles

Species

Koshisaurus katsuyama Shibata & Azuma, 2015

Type species

Named for Katsuyama, a city in Fukui Prefecture, Japan, where fossils of the genus were discovered.

Holotype
FPDM-V9079 , Fukui Prefectural Dinosaur Museum
Material
A nearly completely preserved right maxilla
Horizon
Bonebed IV Bed, Kitadani Formation, Aptian, Early Cretaceous , 121.4–113.2 million years ago
Locality
Kitadani Dinosaur Quarry, Fukui, Japan

References

  1. Shibata, M.; Azuma, Y. (2015). New basal hadrosauroid (Dinosauria: Ornithopoda) from the Lower Cretaceous Kitadani Formation, Fukui, central Japan. Zootaxa 3914(4). Magnolia Press. doi:10.11646/zootaxa.3914.4.3 shibata2015b
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the body length estimate.

    jones2026a
  3. Madzia, D.; Jagt, J. W. M.; Mulder, E. W. A. (2019). Osteology, phylogenetic affinities and taxonomic status of the enigmatic late Maastrichtian ornithopod taxon Orthomerus dolloi (Dinosauria, Ornithischia). Cretaceous Research 108: 104334. Elsevier BV. doi:10.1016/j.cretres.2019.104334

    Osteology and phylogenetic study recovered Koshisaurus as a basal hadrosauroid.

    madzia2019a
  4. Tsogtbaatar, K.; Weishampel, D. B.; Evans, D. C.; Watabe, M. (2019). A new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi Desert (Mongolia). PLOS ONE 14(4): e0208480. Public Library of Science (PLoS). doi:10.1371/journal.pone.0208480

    Described new hadrosauroid recovering Koshisaurus as sister to Hadrosauriformes.

    tsogtbaatar2019a