Cryptarcus
Extinct genus of dinosaurs
From Wikipedia, the free encyclopedia
Cryptarcus is a genus of ceratopsid dinosaur found in the Dinosaur Park Formation of Alberta, dating to the middle Campanian age of the Late Cretaceous.
| Cryptarcus Temporal range: Late Cretaceous (Campanian), | |
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| Holotype skull in multiple view | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ceratopsia |
| Family: | †Ceratopsidae |
| Subfamily: | †Chasmosaurinae |
| Genus: | †Cryptarcus Holmes et al., 2026 |
| Type species | |
| †Chasmosaurus russelli | |
It was first named in 1940 by Charles Mortram Sternberg as a species of the genus Chasmosaurus and given the name Chasmosaurus russelli. The specific name honored Loris Shano Russell, who discovered the first known specimen. It was recognized as part of this genus for several subsequent decades. Throughout the early 21st century it would be considered one of two species of Chasmosaurus, alongside C. belli, and many specimens would be referred to it. However, differences between the original specimen (a nearly complete skull) and other supposed C. russelli specimens were noted, prompting reassessment. New work on the specimen was published in 2026, concluding the former was a distinct species from most of the others. Therefore, it was made the type species of the new genus Cryptarcus, with a partial parietal as the only other specimen retained within the species. While its relationships remain uncertain, it may be more closely related to animals such as Utahceratops and Pentaceratops rather than Chasmosaurus.[1]
Amongst other traits of the skull, it can be distinguished by the deep embayment on the back of its parietal frill and the dome-shape of the ornamentation along the edge of this embayment.[1]
History of research
The specimen that would become the holotype (name-bearing specimen) of Cryptarcus was discovered in 1936 by palaeontologist Loris Shano Russell during his work for the Geological Survey of Canada.[1][2] It was found near the former Onefour Research Station southeast of Manyberries, Alberta, and bears the specimen number CMNFV 8800. Most of the skull was preserved and fully articulated, but the front of the snout, the lower jaws, the right half of the frill, and various portions of the left side of the face were missing and were reconstructed with plaster after recovery of the specimen. Today, the area the specimen was recovered from is known to represent a portion of the Dinosaur Park Formation, known for its diverse assemblage of dinosaurs dating to the Campanian age of the Late Cretaceous. In 1940, Charles Mortram Sternberg interpreted the specimen as a new species of the genus Chasmosaurus, which he named Chasmosaurus russelli in honour of Russell. In addition to the holotype, Sternberg referred three other specimens to his new species, designating them as paratypes. These include CMNVP 8801, a skull lacking the frill, the fragmentary skull CMNVP 8802 (which was destroyed in 1941) and the isolated parietal CMNVP 8803. The association of these specimens with C. russelli was later doubted; the former two do not preserved the necessary anatomical traits to identify them at the species level, and are merely considered indeterminate Chasmosaurus, while CMNVP 8803 shows unusual anatomy and its identity remains uncertain.[1][3]
Subsequent studies would revise the taxonomy of Chasmosaurus, for which seven different species have been named, and a two species model emerged where only C. russelli and the type species C. belli were recognized. A number of Chasmosaurus specimens were referred to C. russelli. Ostensibly, C. russelli was found in the lower layers of the Dinosaur Park Formation (making it older in geologic time), whereas those belonging to C. belli were from the upper layers of the formation.[1][4][5] However, only one specimen other than the holotype has a definitively known stratigraphic height within the formation.[4] Furthermore, rediscovery of the quarry where Sternberg discovered the holotype revealed it to be from a high layer of the Dinosaur Park Formation.[1][4][5] The anatomical distinction of C. russelli and C. belli also proved troublesome, partially due to the large amount of anatomical variation seen in Chasmosaurus. Traits such as the orientation of the lateral bars of the parietal, the size of the horns, and the relative size of the epiparietal ornamentation on the frill proved to be variably distributed across the two species. As such, the division between C. russelli and C. belli became drawn based upon the angle of the median embayment, a "dip" in the shape of the top of the frill. C. russelli had embayments formed by left and right posterior parietal bars meeting at angle between 89° and 128°, whereas those of C. belli met an angle between 136° and 180°.[5] In 2010 Nick Longrich argued many of the specimens referred to C. russelli actually represented a new genus and species, Mojoceratops perifania, but this was rejected by most other researchers. A further complication to the two species model was raised when it was noted that the holotype of C. russelli seemed to be anatomically distinct from the other specimens referred to the species.[1][4]
In 2026, a study by Robert B. Holmes, Jordan C. Mallon, Michael J. Ryan, and David C. Evans reevaluated the holotype and reprepared it to clarify the anatomy obscured by plaster reconstruction. Finding support for its anatomical distinction from other "Chasmosaurus russelli" specimens, they made C. russelli the type species of the new genus Cryptarcus. The generic name is derived from the Latin crypticus, meaning "hidden", and arcus, meaning "arch", referencing to the genus being "hidden" within Chasmosaurus since its initial naming as well as the anatomy of the back of the parietal. They noted that ongoing issues in the taxonomy of chasmosaurs made definitive classification difficult, and noted it was possible Cryptarcus may later become associated with another genus, the lack of any definite link to Chasmosaurus made it most responsible to give it a distinct genus. The other former specimens of C. russelli were considered unrelated, and left in the genus Chasmosaurus pending dedicated study. In addition to the holotype, they recognized the partial parietal TMP 2013.019.0038 as belonging to the species. It was discovered in 2013 in the Onefour area by Wendy Sloboda on the Sage Creek Grazing Reserve, 5.7 kilometres (3.5 miles) east of the holotype quarry and slightly higher in the Dinosaur Park Formation. A large isolated horn, CMNFV 55193, was also discovered in the Onefour area and was noted as possibly representing C. russelli as it does not conform to any other known ceratopsid from its horizon, though it contains no diagnostic characters of the holotype.[1]
Classification
Revision of the material and taxonomy of Cryptarcus found that CMN 8800 was not able to be resolved as closer to either Chasmosaurus or Pentaceratops, with alternative methodologies finding both options possible. Anatomical features that were believed to unite Cryptarcus with Chasmosaurus (low facial profile, rear maxilla hidden below jugal, thin parietal strut) can also be seen among other chasmosaurines and can be subject to taphonomic distortion. The lack of a postorbital horncore, shared with Chasmosaurus, may also be subject to resorption during growth and therefore not a unique feature. Phylogenetic results following the reassessment of Holmes and colleagues (2026) are shown below, based on Iterations 1 and 2 (no weighting). Iterations 3 and 5 (k = 3) recovered Cryptarcus in an unresolved polytomy with Agujaceratops spp., more closely related to Pentaceratops than Chasmosaurus, while Iterations 4 and 6 (k = 12) recovered it closer to Chasmosaurus than Pentaceratops.[1]
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