Fona herzogae

This whole thing started from a website called Thescelosaurus!, so unsurprisingly I'm particularly interested when an old-fashioned "hypsil" metaphorically crosses my desk. Our (belated) guest today is the new genus and species Fona herzogae. Before we get into the meat of the post, I would also like to throw a kind word to the iguanodontian Comptonatus chasei Lockwood et al. (2024), published online the same day. (Yes, it *did* make me think of Camptonotus, which would have been Camptosaurus had somebody not pinned it to a cricket first.)

Genus and Species: Fona herzogae. "Fona" is a reference to an ancestral founding figure of the CHamorro people of the Mariana Islands, used for multilayered reasons (Avrahami et al. 2024); the discussion of the etymology is more than 300 words long and as such should be read in context rather than some guy's blog, but the upshot is the choice of Fona is "rooted in the story of Pontan's sacrifice and Fo'na's love for her brother, highlights the CHamoru values of inafa'måolek (to make good for all), geftåo (the need for compassion, selflessness, and familial bonds)... the importance of the equality shared between women and men... and ongoing efforts to decolonize paleontology" (Avrahami et al. 2024; ellipses for citations omitted here). The lead author Haviv Avrahami adds in an interview that the name is also a way to honor his mother, who is from Guam. The species name "herzogae" honors Lisa Herzog, "(discoverer of the Mini Troll locality) for her unparalleled dedication to the paleontology program at the NCSM [North Carolina Science Museum, Raleigh, North Carolina] and the collection, care, and conservation of fossil specimens worldwide" (Avrahami et al. 2024).

Citation: Avrahami, H. M., P. J. Makovicky, R. T. Tucker, and L. E. Zanno. 2024. A new semi‐fossorial thescelosaurine dinosaur from the Cenomanian‐age Mussentuchit Member of the Cedar Mountain Formation, Utah. The Anatomical Record. doi: https://doi.org/10.1002/ar.25505.

Geography and Stratigraphy: The holotype of F. herzogae is from the Karmic Orodromine locality in Emery County, south-central Utah, United States. Stratigraphically, the site is in the lower Mussentuchit Member of the Cedar Mountain Formation, below the Last Chance Sandstone (99.466 +0.046/-0.053 Ma [million years ago]). Two other sites with F. herzogae specimens are above the Last Chance Sandstone but older than 99.231 +0.090/-0.052 Ma (Avrahami et al. 2024). Therefore, we're just a hair into the Cenomanian stage of the Late Cretaceous.

Holotype: NCSM 33548, "a single partially articulated, nearly complete skeleton" (Avrahami et al. 2024).

Composite skull and mandible of Fona herzogae. Figure 3 in Avrahami et al. (2024), which see for complete caption (CC BY-NC-ND 4.0).

Fona herzogae immediately leaps to the status of one of the most abundant dinosaurs of the Mussentuchit, after Eolambia, the "early lambeosaurine" that wasn't (Avrahami et al. 2024). It also immediately leaps to the status of one of the best-known "hypsils". Not only is there the nearly complete type specimen, several other individuals from at least two other sites are known, including juveniles. Despite all of this material, most of the differences between it and other "hypsils" are pretty subtle (Figure 5 in Avrahami et al. 2024 is a handy visual guide to the differences). Far be it for me to say "seen one, seen 'em all", but "hypsilophodonts"/basal ornithopods/basal neornithischians/what-have-you definitely tended to share a structural type. If I were to ask the typical reader of this blog to describe or draw or otherwise define a general "hypsil"/etc., the end result would probably look a lot like Fona. It would also probably look a lot like Orodromeus, and Parksosaurus, and Hypsilophodon, etc. In fact, about the only one we know of with obvious visible differences is chunky old Thescelosaurus with its long femur and short tibia, proud scion of an evolutionary lineage that was sick and tired of the whole "dinosaurian gazelle" thing. (This makes it a bit ironic that Thescelosauridae is the new Hypsilophodontidae, but that's the way priority crumbles.)

Quarry map of assorted Fona bones. Some assembly required. Figure 4 in Avrahami et al. (2024), which see for complete caption (CC BY-NC-ND 4.0).

The substantial material available for F. herzogae provides a rare opportunity to document variation within a species, and it does not disappoint. Minor differences are present in just about every bone, even after taking into account the taphonomy (with some interesting implications and effects; see below) (Avrahami et al. 2024). Since we have different ages of individuals and different sites, it's easy to come up with many potential drivers: individual variation (including variation of paired bones within individuals), variation due to age, sexual dimorphism, minor shifts in anatomy over time...

About that taphonomy: F. herzogae shows an interesting tendency to be found as tightly packed elements, sometimes partially or fully articulated (Avrahami et al. 2024). By "tightly packed", we're talking about 1 x 2 m blocks (3.3 x 6.6 ft). Meanwhile, other dinosaurs in the Mussentuchit are found in dispersed bone beds. As shown by the anatomically similar Oryctodromeus, there is one surefire way to keep thescelosaurs tightly packed: burrows. An actual burrow has not yet been observed, but that could be due to the paleoenvironment. Nor is it known if F. herzogae dug burrows themselves or if they borrowed them, although it looks likely they weren't dragged in as food due to the absence of predator traces (Avrahami et al. 2024).

In Avrahami et al. (2024), the solution to the eternal terminological problem for "hypsils" is the acronym SBEDO, for "small-bodied early diverging* ornithischian". This is useful because of the explosion of "hypsils" across several different lineages; the darn things aren't as neat as "prosauropods", which can all be called basal sauropodomorphs with no cost except extra letters and aesthetics. F. herzogae's home is determined to be Thescelosauridae as the earliest known thescelosaurine. There are some unusual results in their analysis, including Oryctodromeus hopping to Thescelosaurinae instead of Orodrominae, Parksosaurus refraining from joining the thescelosaurid fun, and Micropachycephalosaurus and Kulindadromeus sometimes joining.** (To be honest, after seeing phylogenetic analyses for nearly 30 years, everybody's got something atypical happening in theirs, or they're not trying hard enough. If you're curious for an alternative fresh take on SBEDOs, I recommend Fonseca et al. 2024, which I used to revamp ornithischians over on The Compact Thescelosaurus.)

*If you haven't been following the literature the past few years, "early diverging" in practice functions like "basal", which in turn replaced "primitive".

**There is a disconnect in their phylogenetic figure (Figure 34) and the caption: the figure just has Thescelosauridae, while the caption indicates there was originally a figure that depicted more of Ornithischia. Captions are sneaky devils for review and editing!

As the authors note, F. herzogae as a thescelosaurine provides a deeper ancestral paper trail to a clade that otherwise just seems to appear out of nowhere with a significant ghost lineage. It also would show two clades of thescelosaurids coexisting for tens of millions of years in North America. The waters are muddied somewhat by F. herzogae's phylogenetic buddy Oryctodromeus making a special appearance in Thescelosaurinae after being with the orodromines all these years, so the story is probably not yet fully revealed. An interesting question, not yet addressed, is what might the functional differences have been between orodromines and thescelosaurines?

References

Avrahami, H. M., P. J. Makovicky, R. T. Tucker, and L. E. Zanno. 2024. A new semi‐fossorial thescelosaurine dinosaur from the Cenomanian‐age Mussentuchit Member of the Cedar Mountain Formation, Utah. The Anatomical Record. doi: https://doi.org/10.1002/ar.25505.

Fonseca, A. O., I. J. Reid, A. Venner, R. J. Duncan, M. S. Garcia, and R. T. Müller. 2024. A comprehensive phylogenetic analysis on early ornithischian evolution. Journal of Systematic Palaeontology 22(1):2346577. doi: https://doi.org/10.1080/14772019.2024.2346577.

Lockwood, J. A. F., D. M. Martill, and S. C. R. Maidment. 2024. Comptonatus chasei, a new iguanodontian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight, southern England. Journal of Systematic Palaeontology 22(1):2346573. doi: https://doi.org/10.1080/14772019.2024.2346573.