Recently Barrett and Maidment (2025) published a paper on the state of Morrison hypsilophodont-things, which is of great interest here because after two long posts on Nanosaurus agilis, we're solidly invested in its fate. How did it fare? Short answer: not very well. But, on the other hand, neither did anybody else. Well, Drinker was shown more appreciation than probably anyone has given it since 1990, but that's not saying much.
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| So, what to call these happy fellows at the Denver Museum of Nature and Science? |
Barrett and Maidment (2025) went over the type specimens of N. agilis, N. rex (Othnielia), Laosaurus celer, L. consors (Othnielosaurus), L. gracilis, and, via illustrations, Drinker nisti. (There is a slight advance on Carpenter and Galton 2018, in that we now get the implication that Bob Bakker has D. nisti as opposed to the whereabouts being unknown.) They find none of the type specimens to be diagnostic. The one that comes off the worst is L. consors. Material cataloged as the type is an assemblage rather than an individual. To be fair, Marsh knew he had multiple individuals at the time, but then he should have been more careful about specifying a type. The parts that had been on display as a panel mount at Yale may be one associated individual, consisting of most of the cervical and dorsal series (just centra), possibly six sacrals, parts of the left shoulder girdle and the pelvis, a partial left femur and complete left foot, and parts of the right femur, tibia, and astragalus. This is a lot of parts/partials plus a lot of plaster, which is not encouraging. The rest of the material is a chimeric mix including at least juvenile dryosaur and hypsil material. The only one of the six that ends up being interesting is D. nisti, which has some dental and jugal features reminiscent of pachycephalosaurs (but is still not diagnostic, although it would be nice to have the type material in hand to be sure).
Where does this leave the Morrison hypsil(s), which Carpenter and Galton (2018) had declared N. agilis? Anonymous, for the time being. Carpenter and Galton (2018) looked upon the pile of Morrison hypsil bits and proposed it was "all" Nanosaurus agilis. Barrett and Maidment (2025) looked upon the same pile and clutch of names and regarded it as a taxonomic dead end, to be set aside to allow a fresh start for more complete and better preserved specimens (with quarry maps and documented associations and such).
At heart, we're seeing two different approaches to taxonomy, and which one you choose depends on how pragmatic you are and how bound you feel by existing names. If you want a species with a holotype featuring robust apomorphies, N. agilis is not for you. We saw that in the comments section of the last post: most of the characters cited by Carpenter and Galton (2018) are widely distributed among hypsil-things, with just a couple that might have some particular use. However: Is there a hypsil-thing in the Morrison that is anatomically
consistent across specimens, whether or not said specimens are
diagnostic across Ornithischia? If so, is it reasonable to call this
hypsil *something*, knowing that it may be revised later? If so, the oldest existing name is Nanosaurus agilis. If you go that route, I'd recommend looking into a neotype, though. ("All would be well, if, if, if, if, if...")
References
Barrett, P. M., and S. C. R. Maidment. 2025. A review of Nanosaurus agilis Marsh and other small-bodied Morrison Formation “ornithopods". Bulletin of the Peabody Museum of Natural History 66(1): 25–50. doi: https://doi.org/10.3374/014.066.0102.
Carpenter, K., and P. M. Galton. 2018. A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA. Geology of the Intermountain West 5:167–207. doi:
I'll repeat my comment from the Dinosaur Mailing Group on this paper, as it demonstrates just what a poor job the authors did when evaluating diagnosability.
ReplyDeleteI'm inherently untrusting of Maidment's claims of nomen dubium, as she is quick to point out prior suggested diagnostic characters are primitive or shared with other taxa, while never saying e.g. "Nanosaurus can't be distinguished from valid taxa X and Y", and much like Nesbitt just relies on published character lists. As an obvious example here, Barrett and Maidment note that Galton (1978) diagnosed Nanosaurus in part by "(G5) fourth trochanter index of femur about 0.43; and (G6) tibia about 115% of femur length." Their reply is-
"The fourth trochanter index (G5) appears to relate to how proximally the fourth trochanter is positioned. The “index” given by Galton (1978) indicates the fourth trochanter is on the proximal part of the femoral shaft, a feature that is plesiomorphic for Ornithischia (Butler et al. 2008; Boyd 2015). Similarly, a tibia that is longer than the femur (G6) is a feature shared by all bipedal ornithischians and is also an ornithischian plesiomorphy (Maidment and Barrett 2012)."
I have zero opinion on whether Nanosaurus is valid or not, but you can't just take "about 0.43" and "about 115%" and change that to <0.5 and >100% respectively to dismiss their value as characters.
I'll also repeat my comment from the Dinosaur Mailing Group:
ReplyDelete"Notwithstanding that the holotype and referred material for _Drinker_ are insufficiently figured/described, there might be enough wiggle-room to regard it as a provisionally valid genus. Although Barrett & Maidment found its dental and jugal characters to be indistinguishable from pachycephalosaurs like _Dracorex_, there are astragalar characters that might differentiate _Drinker_ from known pachycephalosaurs. It's slim pickings; but perhaps enough to uphold the validity of _Drinker_. This assumes that the holotype (CPS 106) craniodental and postcranial material come from the same individual, as stated by Bakker &c (1990). "
Also I agree that the "Bob Bakker has D. nisti as opposed to the whereabouts being unknown" is (somewhat) reassuring.
Recycling yet another of my comments from the Dinosaur Mailing Group (this time regarding erstwhile _Nanosaurus_ material):
ReplyDelete"There is the potential for a new taxa to be described, including based on the headless partial skeleton BYU ESM 163R (originally described by Galton & Jensen, 1973, as "_Nanosaurus (?) rex_"). Note that Boyd (2015) erroneously regarded BYU ESM 163R as the holotype of _Othnielosaurus consors_; this specimen, and another headless partial skeleton UW 24823, were regarded as representing a single taxon in Boyd's comprehensive phylogenetic analysis. If these specimens, as well as NMZ 1000010 ("Barbara", the most complete), pertain to the same genus and species, there is the promise of a very well-known new Morrison neornithischian."
Maybe one of these specimens could serve as a neotype for _Nanosaurus agilis_? Or perhaps it's better to just shitcan this genus/species name altogether (too much baggage) and pick a new one.
BTW, nice article Justin.
Thank you! "Neotype or bust" is pretty much my feeling on it by now as well, as YPM 1913 is... well, it's doing its best. The funny thing about BYU ESM 163R is I wouldn't be surprised if *everyone* in the field who was born between about 1970 and whenever "Barbara" came to attention has it as their ingrained image of what the Morrison "hypsil" is supposed to be. Of course, the catch with using it as a type for anything is that ornithischian people don't like when there isn't a skull.
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