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| Cimolodon desosai Mantilla, Newbins, Fastovsky, Zhang, Montellano-Ballesteros, Alcántara & Chen, 2026 Illustration by Andrey Atuchin |
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.
SYSTEMATIC PALEONTOLOGY
MAMMALIA Linnaeus, 1758
MULTITUBERCULATA Cope, 1884
CIMOLODONTA McKenna, 1975
PTILODONTOIDEA Sloan and Van Valen, 1965
CIMOLODONTIDAE McKenna, 1975
CIMOLODON Marsh, 1889
CIMOLODON DESOSAI, sp. nov.
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| Partial cranium of the holotype of Cimolodon desosai (IGM 14691). Images are three-dimensional surface renderings from μCT scans in: A, anterior; B, stereo dorsal; C, stereo ventral; D, left lateral; and E, right lateral views of the partial cranium; and F, occlusal view of the right upper cheek tooth row in high magnification. Dashed white lines represent interpreted position of cranial bone sutures. Abbreviations: al, anterior lamina; fr, frontal; iof, intraorbital foramen; mx, maxilla; na, nasal; naf, nasal foramen; otc, orbitotemporal canal; pa, parietal; pav, palatal vacuity; pmx, premaxilla; pop, postorbital process; sq, squamosal; zpm, zygomatic process of the maxilla. Scale bar equals 10 mm for A–E and 2 mm for F. |
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| 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. Illustration by Andrey Atuchin |
Gregory P. Wilson Mantilla, Isiah R. Newbins, David E. Fastovsky, Yue Zhang, Marisol Montellano-Ballesteros, Dalia García Alcántara and Meng Chen. 2026. 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. Journal of Vertebrate Paleontology. e2641109. DOI: doi.org/10.1080/02724634.2026.2641109 [22 Apr 2026]
