Cifelliodon
| Cifelliodon Temporal range: Early Cretaceous,
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Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Clade: | Cynodontia |
| Clade: | Mammaliaformes |
| Genus: | †Cifelliodon Huttenlocker et al., 2018 |
| Type species | |
| †Cifelliodon wahkarmoosuch Huttenlocker et al., 2018
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Cifelliodon is an extinct genus of mammaliaforms. The type species, Cifelliodon wahkarmoosuch, was described based on a skull from the Cedar Mountain Formation in Utah, United States, dated to the Early Cretaceous. The skull is well preserved and large for a mammaliaform of its age. Its teeth were compared to those of the hammer-headed bat, a fruit-eater, while scans of the inner skull allowed for hypotheses regarding brain structure and function. Some of its features resemble those of mammaliamorphs of the Triassic, while others are seen in crown members of Mammalia.
The classification of Cifelliodon has been disputed, with the genus variously labelled a haramiyidan, an allotherian, or neither. The researchers who described it labelled it as evidence that mammaliamorphs with large bodies and diverse ecological roles lived in North America during the Early Cretaceous. The Yellow Cat Member, believed to represent a long span of geologic time, has also yielded remains of a range of dinosaurs.
Discovery and naming
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Cifelliodon was described by the American paleontologist Adam Huttenlocker and colleagues in 2018 based on an "exceptionally preserved skull". The skull was recovered from the Yellow Cat Member of the Cedar Mountain Formation. The site is Early Cretaceous in age, between 139 and 124 million years old according to radiometric dating estimates. The type species of the genus Cifelliodon was named Cifelliodon wahkarmoosuch. Cifelliodon means 'Cifelli's tooth', in honor of the mammal paleontologist Richard Cifelli, while wahkarmoosuch comes from the Ute words for 'yellow' (wahkar) and 'cat' (moosuch).[1]
Description
[edit]The skull of Cifelliodon was noted for its large size relative to those of other mammaliaforms of the Mesozoic: 70 millimeters (2.8 in) in length, corresponding to an estimated total body mass of 0.91–1.27 kilograms (2.0–2.8 lb). Most of its upper dental features are missing, but two alveoli (tooth sockets), belonging to the incisors; one canine; and four postcanines, including an unerupted pair of molars, are preserved. The incisor roots are reclined back and converge centrally, indicating procumbency (inclination toward the lips). The alveoli of the postcanines appear to be similar in diameter to that of the canine. The final molar possesses a well-defined central valley that is closed-off from the front by a tall cusp (raised tooth point), as well as a lingual (tongue-facing) ridge that connects to a posterolingual (at the base of the tongue) cusp below, a pattern which the researchers compared with the teeth of the hammer-headed bat (Hypsignathus monstrosus), a fruit-eater. The molar was noted for its extensive similarity, aside from size and proportion, to that of Hahnodon taqueti, a mammaliaform from the Early Cretaceous of Morocco which had been previously identified as a multituberculate. Huttenlocker and colleagues wrote that the features of the molars of Cifelliodon and H. taqueti appeared more haramiyidan than multituberculate.[1]
The type specimen also displays a variety of ancient traits more commonly seen in mammaliamorphs of the Triassic in than those of the Cretaceous. The include the shape of its parietal bones, which are waisted along their lateral sides rather than bulging outward; the presence of a tabular bone; and the extension of the front part of the jugal bone. However, some of the features exhibited are found in crown-group mammals, including an extensive process (outgrowth of tissue) on the premaxilla that borders the nasal region; reduced premaxilla process between the nostrils; and the limited extent of the rear end of the jugal bone. X-ray-computed tomography of the inner skull revealed traits intermediate between primitive mammal relatives and crown mammals. The size of the cranial vault was described as "modest", with an encephalization quotient (a measure of actual brain mass compared to expected brain mass based on body size) of between 0.25 and 0.30, which the authors wrote was smaller than those of the mammaliaform Hadrocodium and the Cretaceous crown mammals Vincelestes and Pucadelphys. They also wrote that much of the brain volume would have been taken up by olfactory bulbs and the piriform cortex (both associated with the sense of smell). The neocortex would have been small, its features poorly defined, especially compared with those of Cretaceous crown mammals. The authors concluded that the features of the brain support the hypothesis that haramiyidan brain development and behavior were primarily scent-oriented.[1]
Classification
[edit]In their description of Cifelliodon, Huttenlocker and colleagues expressed support for the recognition of Haramiyida, the order to which they assigned Cifelliodon, as a monophyletic group closely related to Mammalia, as opposed to belonging to Mammalia itself as a relative to the multituberculates, as some authors had proposed. They defined Haramiyida as all mammaliaforms more closely related to Thomasia and Haramiyavia than to Didelphis and placed Cifelliodon as forming a polytomy with Hahnodon and Vintana, the latter of which is a gondwanathere. Their study supported the placement of Gondwanatheria within Haramiyida and outside of Mammalia. They wrote that the well preserved remains of Cifelliodon supported the relationship of hahnodontids to Haramiyida (placing the former group within the latter).[1]
In 2020, the Canadian paleontologist David W. Krause and colleagues reassessed the relationships of mammaliaform lineages and placed Cifelliodon within Mammalia at the base of Allotheria. According to their work, Allotheria also contains Euharamiyida and a clade formed by Multituberculata and Gondwanatheria. The haramiyidans Haramiyavia and Thomasia, as well as the poorly studied Megaconus, were placed outside of Mammaliaformes altogether.[2] The placement of Cifelliodon within Allotheria was supported by the Chinese paleontologist Fangyuan Mao and colleagues, although they placed it as the sister group of a clade formed by Euharamiyida and Gondwanatheria and also moved Haramiyavia and Thomasia within Allotheria.[3] A September 2023 study by the Chinese paleontologist Zhiqiang Yu and colleagues instead placed Cifelliodon outside of Mammalia and as a close relation of Haramiyavia and Thomasia (all three of which were placed within Mammaliaformes). This study rejected the idea of Haramiyida as a monophyletic group, finding no close relation between the three aforementioned genera and euharamiyidans (with the latter group recognized as crown mammals).[4]
Paleoecology
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The skull of Cifelliodon is have been remarkably large for an Early Cretaceous mammal. The animal would have been approximately the size of a medium hare at a time when most mammals were around shrew- or mouse-sized. Only one known North American contemporary was larger: the carnivorous Gobiconodon ostromi.[5] Huttenlocker and colleagues wrote that the discovery of Cifelliodon supported the idea that haramiyidans, with which they classified the genus, survived until the Early Cretaceous and ranged across the ancients continents of Laurasia and Gondwana. They also described the presence of related dinosaur taxa across the continents as evidence of later intercontinental links than previously thought. They identified the mid-Cretaceous radiation of other mammalian groups, namely multituberculates and tribosphenids, as coinciding with the extinctions of many of their more primitive relatives. They labelled Cifelliodon as evidence that large-bodied mammaliamorphs with diverse ecological roles persisted in North American ecosystems until the mid-Cretaceous.[1]
The Yellow Cat Member is known for its well-preserved dinosaur fossils, which are believed to record a relatively long span of geologic time.[6] The Yellow Cat Member is distinct from other geologic units of the Cedar Mountain Formation, with its own relict vertebrate fauna with Jurassic affinities similar to the Wealden fauna of Europe. Dinosaurs found include iguanodontids, polacanthids (ankylosaurs), and brachiosaurids (sauropods). Theropod dinosaurs include Utahraptor ostrommaysorum and Nedcolbertia justinhofmanni.[7]
See also
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References
[edit]- ^ a b c d e Huttenlocker, Adam K.; Grossnickle, David M.; Kirkland, James I.; Schultz, Julia A.; Luo, Zhe-Xi (June 2018). "Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana". Nature. 558 (7708): 108–112. doi:10.1038/s41586-018-0126-y.
- ^ Krause, David W.; Hoffmann, Simone; Hu, Yaoming; Wible, John R.; Rougier, Guillermo W.; Kirk, E. Christopher; Groenke, Joseph R.; Rogers, Raymond R.; Rossie, James B.; Schultz, Julia A.; Evans, Alistair R.; von Koenigswald, Wighart; Rahantarisoa, Lydia J. (May 2020). "Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity". Nature. 581 (7809): 421–427. doi:10.1038/s41586-020-2234-8. ISSN 1476-4687. Retrieved 22 February 2026.
- ^ Mao, Fangyuan; Li, Zhiheng; Hooker, Jerry J; Meng, Jin (11 July 2023). "A new euharamiyidan, Mirusodens caii (Mammalia: Euharamiyida), from the Jurassic Yanliao Biota and evolution of allotherian mammals". Zoological Journal of the Linnean Society. 199 (3): 832–859. doi:10.1093/zoolinnean/zlad050. ISSN 0024-4082. Retrieved 22 February 2026.
- ^ Yu, Zhiqiang; Wang, Haibing; Zhang, Chi; Dong, Liping; Huyskens, Magdalena H.; Cui, Zexian; Cary, Paige; Di, Yankun; Amelin, Yuri; Li, Gang; Li, Qiuli; Xia, Xiao-Ping; Deng, Chenglong; Wang, Yuanqing; He, Huaiyu; Yin, Qing-Zhu (1 September 2023). "Temporal framework for the Yanliao Biota and timing of the origin of crown mammals". Earth and Planetary Science Letters. 617. doi:10.1016/j.epsl.2023.118246. ISSN 0012-821X. Retrieved 22 February 2026.
- ^ Hoffmann, Simone; Krause, David W. (June 2018). "A 3D view of early mammals". Nature. 558 (7708): 32–33. doi:10.1038/d41586-018-05134-9. Retrieved 25 February 2026.
- ^ Joeckel, Robert M.; Suarez, Celina A.; McLean, Noah M.; Möller, Andreas; Ludvigson, Gregory A.; Suarez, Marina B.; Kirkland, James I.; Andrew, Joseph; Kiessling, Spencer; Hatzell, Garrett A. (26 January 2023). "Berriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA". Geosciences. 13 (2): 32. doi:10.3390/geosciences13020032.
- ^ Garrison, James R.; Brinkman, Donald; Nichols, Douglas J.; Layer, Paul; Burge, Donald; Thayn, Denise (1 June 2007). "A multidisciplinary study of the Lower Cretaceous Cedar Mountain Formation, Mussentuchit Wash, Utah: a determination of the paleoenvironment and paleoecology of the Eolambia caroljonesa dinosaur quarry". Cretaceous Research. 28 (3): 461–494. doi:10.1016/j.cretres.2006.07.007. ISSN 0195-6671. Retrieved 27 February 2026.
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