Sphaerotholus buchholtzae
Sphaerotholus buchholtzae model, WIP. Model primarily based on Stegorceras due to extremely fragmentary nature of Sphaerotholus material.
Sphaerotholus buchholtzae was a highly derived Pachycephalosaur, initially described from a partial skull. The genus Sphaerotholus was quite long-lived, with the earliest species S. goodwini from the Late Campanian showing that this genus lasted for at least 7-8 million years (Carr and Williamson, 2002).
Some researchers believe that this taxon is actually synonymous with Prenocephale edmontonensis (Sullivan, 2003), though recent research based on new S. buchholtzae material (a complete postorbital) seems to support its status as a distinct taxon (Mallon et al., 2015).
"Leptorhynchos" elegans
[Model for this taxon has not been made yet, as I need a copy of the Anzu model to make it]
The reason the scientific name is in quotation marks in this case is because the remains from Hell Creek are assigned to this species but most likely represent a unique taxon (whether this is a new genus or just a new species of Leptorhynchos is uncertain), and thus this name is being used until a new name is proposed and accepted. Leptorhynchos elegans was a species of Caenagnathid Oviraptorosaur (belonging to the same family as Anzu), known from the Late Campanian of Western North America. Distinct characters for this genus include small size, a short, robust mandible, and an upturned tip of the beak (Longrich et al., 2013). In the future I will try to communicate with these authors and perhaps others so that I can figure out the best way to go about making a model of the similar taxon from Hell Creek.
Avisaurus archibaldi
Avisaurus archibaldi model, WIP. In-game version will be feathered.
Avisaurus archibaldi was one of several avian theropods from the Hell Creek formation, and unfortunately both A. archibaldi and its sister taxon A. gloriae are known only from the tarsometatarsus (a single bone in the foot) (Varrichio et al., 1995). Avisaurus was a genus of enantiornithine - the most abundant group of avian dinosaurs in the Mesozoic. They were extremely similar to modern birds, though most retained teeth and clawed fingers on their wings. The tarsometatarsus of A. archibaldi measures 73.9mm, which is the longest known in any enantiornithine (Varrichio et al., 1995). It was one of the largest volant [flying] dinosaurs from the Late Cretaceous, with an estimated mass of 5kg (Longrich et al., 2011).
Cimolopteryx maxima
[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]
C. maxima was a species of Charadiiforme bird, known from several late Maastrichtian formations. It was a rather small bird, approximately the size of a small gull (Hope, 2002). It is known almost exclusively from isolated coracoids, though their anatomy is distinct enough for several species to be identified (currently four species are recognized). C. maxima was an estimated 2kg in weight (Longrich et al., 2011).
Brodavis
[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]
B. baileyi was a species of freshwater hesperornithiform bird, known only from the holotype - a single left metatarsal. The genus Brodavis belongs to its own family, Brodavidae. Interestingly, while the marine members of the Hesperornithoform order appear to have lost volant abilities by the end of the Cretaceous, the minimal amount of pachyostosis in Brodavis suggests that it may have had at least a limited ability to fly (Martin, 2012). One of the unnamed Hesperornithiforms from Hell Creek was also attributed to a second species in this genus, Brodavis americanus.
Potamornis skutchi
[Remains too fragmentary to reconstruct a model without thorough collaboration with paleontologists]
Potamornis was another hesperornithiform, described from remains collected from the Lance Formation - remains from Hell Creek have been attributed to this taxon. While it was almost certainly a member of the Hesperornithes clade, its precise relationships within the group are not certain. Though, it does share the unique pterygoid articulation with the family Hesperornithidae (and poorly defined [or even absent] division of the head), the hinge-like temporal articulation, exceptionally small orbital process, and prominent attachment site for the deep layers of the protractor pterygoidei et quadrati muscle as well as several other details set it apart. These unique characters, combined with its smaller size (roughly 1.5-2kg), seem to suggest a feeding specialization differing from that of Hesperornithidae (Elzanowski et al., 2001).
Unnamed taxa:
There are three ornithurine taxa that currently lack formal names, though they are informally referred to as "Ornithurine B", "Ornithurine C", and "Ornithurine D". Each of the three are known only from partial coracoids, and as such there is not enough material to publish a sufficient description for a new taxon. Size estimates based on a graph in Longrich et al. (2011) estimates masses of around 500-600g for "Ornithurine B", 700-800g for "Ornithurine D", and around 2.9-3kg for "Ornithurine C". Since the data was presented as a bar graph rather than a table of mass estimates, these numbers are my estimates based on what I can see, so I could certainly be wrong. I would encourage anyone to look at the original literature and make your own informed decision.
I hope this Creature Feature has filled your brains with more knowledge about some of the more mysterious taxa from Hell Creek! There are one [possibly two] more dinosaur taxa for me to cover, but after that I will be doing more of these grab-bag Creature Features due to many of the other vertebrate fauna being rather fragmentary.
Acknowledgements:
Carr, T. E.; Williamson, T. D. 2002. A new genus of highly derived pachycephalosaurian from western North America. Journal of Vertebrate Paleontology 22 (4): 779-801.
Sullivan, Robert M. 2003. Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae). Journal of Vertebrate Paleontology 23 (1): 181-207.Mallon, Jordan C.; Evans, David C.; Tokaryk, Tim T.; Currie, Margaret L. First pachycephalosaurid (Dinosauria: Ornithischia) from the Frenchman Formation (upper Maastrichtian of Saskatchewan, Canada. Cretaceous Research 56: 426-431.
Longrich, N. R.; Barnes, K.; Clark, S.; Millar, L. 2013. Correction to Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a Revision of the Caenagnathinae. Bulletin of the Peabody Museum of Natural History 54 (2): 263.
Varrichio, David J., Chiappe, Luis M. 1995. A New Enantiornithine Bird From the Upper Cretaceous Two medicine Formation of Montana. Journal of Vertebrate Paleontology 15 (1): 201 - 204.
Longrich, Nicholas R.; Tokaryk, Tim; Field, Daniel J. 2011. Mass Extinction of Birds at the Cretaceous–paleogene (k-pg) Boundary. Proceedings of the National Academy of Sciences of the United States of America 108 (37): 15253-15257.
Hope, S. 2002. The Mesozoic radiation of Neornithes. 339-388 In: Chiappe, L.M. and Witmer, L. (eds.), Mesozoic Birds: Above the Heads of Dinosaurs.
Martin, Larry D.; Kurochkin, Evgeny N.; Tokaryk, Tim. 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld 21 (1): 59-63.
Elzanowski, Andrzej; Paul, Gregory S.; Stidham, Thomas A. 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology 20(4): 712-719
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