Cifelliodon was a prehistoric mammal which lived in Utah during the early Cretaceous Period approximately 135 million years ago.

The only specimen which we have of this animal is a single upper jaw measuring 2.75 inches (7 cm) long which was found in eastern Utah in 2004. The locality where the fossil was found was discovered by the paleontologist Andrew R. C. Milner, and for that reason it was named “Andrew’s Site”. The rocks here date to the upper part of the Yellow Cat Member of the Cedar Mountain Formation, 135-132 million years ago. The creature was named Cifelliodon in 2018 in honor of Dr. Richard L. Cifelli, a paleontologist who specializes in prehistoric mammals. The species name wahkarmoosuch comes from the native Ute language, and literally means “yellow cat” because the fossil was found within the upper part of the Yellow Cat Member.

All of the teeth on this specimen are missing except for an un-erupted pair of molars in the back of the jaw. The name Cifelliodon literally means “Cifelli’s tooth”, which is somewhat awkward considering that there are hardly any teeth on the specimen itself.

Upper jaw of Cifelliodon wahkarmoosuch (collection ID code: UMNH VP 16771). A) Dorsal view; B) Ventral view; C) Left lateral view; D) Anterior view; E) Posterior view. Scale bar = 10mm. Image modified from that seen in Huttenlocker et al (2018).

Because the only known specimen of Cifelliodon is a single upper jaw and absolutely nothing else, there’s a lot about this animal’s anatomy that needs to be inferred.

Firstly, what would the entire skull have looked like? Although no teeth themselves were found with the jaw specimen, it had 7 tooth sockets on each side: two incisors, one canine, and four molars. Interestingly, there were no tooth sockets at the very front of the jaw, leaving a prominent gap in the middle. This suggests that the front of the lower jaw had two large incisors which fit into this gap. Such a feature is seen in many extinct and extant mammals, including rodents and even lemurs which are primitive primates.

Skull of the prehistoric allotherian mammal Meniscoessus from the Hell Creek Formation. Cifelliodon likely had a similar overall appearance. Rocky Mountain Dinosaur Resource Center, Woodland Park, Colorado. Photograph by MCDinosaurhunter (November 19, 2008). Creative Commons Attribution-Share Alike 3.0 Unported license.

A prominent sagittal crest running atop the middle of the cranium and large temporal fenestrae indicate that the creature possessed large and very strong jaw muscles. This enabled it to crack through the hard husks of seeds, the exoskeletons of insects or other arthropods, or perhaps the shells of freshwater bivalves, or even crunch through the bones of small vertebrates. Huttenlocker et al (2018) states that the interior of the skull possessed large olfactory areas. This suggests that Cifelliodon had an exceptional sense of smell.

Secondly, how big would the whole animal have been? Huttenlocker et al (2018) gave an estimated body mass of 2-2.8 pounds (0.91-1.27 kg). As mentioned before, Cifelliodon had a skull measuring 2.75 inches long. That’s slightly larger than the skull of a modern-day prairie dog or a muskrat. This is unusually large for a Mesozoic mammal, which were commonly no bigger than mice or rats. We might also be able to extrapolate size by comparing this jaw to other allotherian mammals. One example is Megaconus, which is slightly larger than a modern-day squirrel. Cifelliodon appears to have been around 50% bigger than Megaconus. Again, that’s in the size range of a groundhog or a muskrat.

Skeleton of the prehistoric mammal Megaconus. Zhou, Chang-Fu; Wu, Shaoyuan; Martin, Thomas; Luo, Zhe-Xi (2013). “A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations”. Nature, volume 500, issue 7461 (August 7, 2013). Page 164.

Third, where does Cifelliodon fit on the mammal tree? When it was described in 2018, Cifelliodon was classified as belonging to a group of mammals called “haramiyids”, whose members were previously known only from Morocco. However in 2020, it was re-described as a basal member of the prehistoric mammal group Allotheria. The allotherians first appeared during the middle of the Jurassic Period around 167 million years ago, they survived the Cretaceous extinction, and they persisted until the late Eocene Epoch of the Tertiary Period around 33 million years ago. The clade Allotheria is divided into several sub-clades including Haramiyida, Gondwanatheria, Multituberculata, Triconodonta, and Volaticotheria. Because Cifelliodon was described as a basal member of Allotheria, it didn’t fit into any of that clade’s sub-groups.

Due to the animal’s size and the fact that it lived in a savannah like habitat, one may be tempted to make comparisons of Cifelliodon to modern-day prairie dogs. In fact, due to comparisons which have been made between prehistoric Utah and the modern-day African savannah, it’s probably more appropriate to equate Cifelliodon with modern-day African ground squirrels. However, both of these species are social animals which live in communities. Is there any evidence that Cifelliodon did the same? The short answer is “No”. So far, preserved prehistoric burrows have not been found within the rock layers of the upper Yellow Cat Member. Furthermore, you’d think that we would find multiple skeletons of Cifelliodon if it was a social animal which lived in groups. However, keep in mind that modern-day prairie dogs and ground squirrels usually live in dry areas, and most of the fossils which were recovered from the Cedar Mountain Formation were found in riverine or lake deposits. Burrowing animals like these tend to not dig their burrows in areas where there’s a high water table due to the possibility of flooding. This means that, if Cifelliodon really was a prehistoric analog of a prairie dog, then it likely lived in drier areas where fossilization was unlikely to occur. So, for the time being, I think it’s best to think of Cifelliodon as a solitary animal until proven otherwise.

Below is a reconstruction which I made of Cifelliodon. The body is based upon that of the related allotherian mammal Megaconus from the middle Jurassic Period of China. The resulting image, although unintentional, ended up looking similar to a modern-day Australian marsupial called a numbat. The drawing was made with No.2 pencil and Prismacolor colored pencils on printer paper.

Cifelliodon. © Jason R. Abdale (April 6, 2023).


Huttenlocker, Adam K.; Grossnickle, David M.; Kirkland, James I.; Schultz, Julia A.; Luo, Zhe-Xi (2018). “Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana”. Nature, volume 558, issue 7708 (June 7, 2018). Pages 108-112.

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.; Koenigswald, Wighart von; Rahantarisoa, Lydia J. (2020). “Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity”. Nature, volume 581, issue 7809 (April 29, 2020). Pages 421-427.

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