2026-04-23 ワシントン大学（UW）
An illustration of Cimolodon desosai on the tree with a fruit in its mouth. It was about the size of a golden hamster. It likely scampered on the ground and in the trees and ate fruits and insects. Photo: Andrey Atuchin
＜関連情報＞
- https://www.washington.edu/news/2026/04/23/researchers-discover-the-fossil-of-a-new-hamster-sized-mammal-that-lived-alongside-dinosaurs-on-the-pacific-coast/
- https://www.tandfonline.com/doi/full/10.1080/02724634.2026.2641109
メキシコ、バハ・カリフォルニアの上部白亜紀（カンパニアン期）エル・ガロ層から発見された、新種のキモロドン（哺乳綱、多丘歯目、キモロドン科）の頭蓋骨および体骨格の化石 Cranial and postcranial remains of a new species of Cimolodon (Mammalia, Multituberculata, Cimolodontidae) from the Upper Cretaceous (Campanian) El Gallo Formation of Baja California, México
Gregory P. Wilson Mantilla,Isiah R. Newbins,David E. Fastovsky,Yue Zhang,Marisol Montellano-Ballesteros,Dalia García Alcántara & Meng Chen
Journal of Vertebrate Paleontology Published:22 Apr 2026
DOI:https://doi.org/10.1080/02724634.2026.2641109
ABSTRACT
Late Cretaceous mammals from North America are predominantly known from isolated teeth and fragmentary jaws and from localities representing coastal lowlands along the Western Interior Seaway. Here, we report craniodental and associated postcranial remains of a new species of the cimolodontid multituberculate genus Cimolodon from the Upper Cretaceous (Campanian) El Gallo Formation of Baja California, México. The specimen was deposited along the Pacific Coast between 75.17 ± 0.30 Ma and 74.55 ± 0.18 Ma. It represents the most complete mammal known from the Mesozoic of México and one of the best known cimolodontan multituberculates from North America. Morphologically, the new species, Cimolodon desosai, is most like C. nitidus, but differences include upper anterior premolar shape, molar cusp formulae, and relative length proportions of the cheek teeth. Phylogenetic analysis supports placement of the new species within Cimolodon and Ptilodontoidea, but uncertainties remain regarding relationships among cimolodontan families. Using the craniodental and postcranial data, we quantitatively reconstruct C. desosai as a small-bodied (∼100 g), animal-dominated omnivore with a scansorial locomotor mode. With the new taxonomic occurrence, the El Gallo mammalian local fauna is now known from 16 specimens referred to three multituberculate species (Mesodma cf. M. formosa, ?Stygimys sp., and Cimolodon desosai), one metatherian (Pediomys sp.), and one eutherian (Gallolestes pachymandibularis). Although further sampling is needed, the mammalian local fauna presently shows greatest biogeographic affinities with the Terlingua local fauna of western Texas.
