Cryptarcus, new genus for "Chasmosaurus” russelli from Alberta (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Cryptarcus gen. nov.
Cryptarcus russelli comb. nov.

Robert B. Holmes, Jordan C. Mallon, Michael J. Ryan and David C. Evans (2026)
New information on the holotype of “Chasmosaurus” russelli (Ornithischia: Ceratopsidae) necessitates the establishment of a new genus to receive the species
Canadian Journal of Earth Sciences (advance online publication)
doi: https://doi.org/10.1139/cjes-2025-0031
https://cdnsciencepub.com/doi/10.1139/cjes-2025-0031

Free pdf:
https://cdnsciencepub.com/doi/epdf/10.1139/cjes-2025-0031

Although the holotype of Chasmosaurus russelli Sternberg, 1940, from the upper Dinosaur Park Formation of southern Alberta, shares features with other Chasmosaurus Lambe, 1914 specimens from Dinosaur Provincial Park as well as various chasmosaurine taxa from the southwest United States, it also possesses unique features of the premaxilla and frill epiossifications. An iterative phylogenetic analysis, scoring only the holotype (CMNFV 8800), produces three consensus topologies, one of which places CMNFV 8800 closer to Chasmosaurus than to Pentaceratops, another in which CMNFV 8800 is closer to Pentaceratops than to Chasmosaurus, and a final topology in which these relationships are unresolved. Under current definitions, CMNFV 8800 cannot be accommodated within Chasmosaurus or any other known chasmosaurine genus. Consequently, we erect Cryptarcus gen. nov. to receive it. Cryptarcus russelli comb. nov. may represent a migrant originating from the southern “Pentaceratops clade”, but it may also be part of a lineage more closely related to Chasmosaurus in which Pentaceratops-like features (e.g., frill wider anteriorly than posteriorly, deep parietal embayment, and first epiparietals nearly touch at the midline) evolved convergently. None of our phylogenetic topologies support an anagenetic trend from Cryptarcus russelli through Pentaceratops to produce Terminocavus Fowler and Freedman Fowler, 2020, as has been recently hypothesized.

===

[Mickey Mortimer]

Great looking paper, though I'm not a ceratopsian expert, but I thought the title deserved a comment given recent discussions here on naming new genera for established species. The title claims "New information ... necessitates the establishment of a new genus to receive the species", but the abstract itself shows this isn't the case because in some runs of the analysis russelli is sister to Chasmosaurus (and Mojoceratops, that the authors do not accept as valid). And in other runs, it's in a trichotomy with Chasmosaurus and the Pentaceratops group, so again COULD be Chasmosaurus. Indeed, it's only in the runs using the extreme weighting of k=3 (which was found by Goloboff et al. 2018 to give less accurate results than unweighted or k=3 analyses) that russelli falls within the Pentaceratops group.  So first I would say no strong evidence indicates russelli ISN'T Chasmosaurus. And even if you accept the k=3 topologies as equally probable, it's still uncertain if russelli is Chasmosaurus, so Chasmosaurus? russelli would be just as justified as Cryptarcus russelli, thus nothing necessitated creating Cryptarcus, contra the title.  

The authors confusingly say "One option would be to retain the name “Chasmosaurus” russelli, using scare quotes to denote our uncertainty regarding the generic designation. However, this solution could be misunderstood as suggesting that it is more closely related to Chasmosaurus than to the “Pentaceratops clade”, an implication that is not entirely supported by our results."  But scare quotes would actually indicate russelli was NOT Chasmosaurus, or at least that there's no good reason to think it is, quite the opposite of suggesting it's more closely related to Chasmosaurus than other genera.  And that indeed would be worse than erecting Cryptarcus, since some analyses indicate it could be Chasmosaurus. 

And all of this is even ignoring the assumption genera must be monophyletic, as the k=3 topologies leave the possibility open that russelli is basal to Agujaceratops and the rest of the Pentaceratops group, so that Chasmosaurus (including russelli) could be a paraphyletic grade genus. like Daspletosaurus has been argued to be. 

Not that I have a problem with the creation of Cryptarcus, as ceratopsid workers have been extreme splitters for the last two decades, but it wasn't necessary.

Mickey Mortimer

[Gregory Paul]

Mickey raises some points. The best thing about the paper is that is shows that CMN 2280 is clearly not the same as the C. russelli type, which I did not realize. I wonder why 2280 was not given a new species name. 

The N Amer ceratopsids and lambeosaurines tend to be way over split, with differing species level display features of frills and/or horn/lets and/or crests being used to designate genera despite the rest of the skull and skeleton being similar. This is way my entries in the field guides differ from the standard namings. Putting all these chasmosaurines in Chasmosaurus solves the problems of what is and is not to be a genus. Like Cervus and Tragelaphus. The very varying results of the phylogenetics shows why I am skeptical about relying too much on that factor, grade is also very important. 

GSPaul

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/2b381db0-a1d9-44fc-80ea-1b173bdc0f87n%40googlegroups.com.