#ornithomimus

I’ll be making a poll later today that’s going to be for which ones I should make into keychains, so keep an eye out for that :)

My Mesozoic is Yellow!! Eoraptor - Yinlong - Dilophosaurus

Baryonyx - Quetzalcoatlus - Carcharodontosaurus

Argentinosaurus - Archelon - Homalocephale

Iguanodon - Medusaceratops - Miragaia

Mononykus - Nodosaurus - Ornithomimus

Dromiceiomimus brevitertius

A male in breeding plumage takes shelter from the sleet of a spring coldsnap

The second of my Horseshoe Canyon series. I didn't have any particular knowledge of ornithomimids before this piece and I think I might actually know less now that I've completed it. Specifically, this taxon in particular has been problematic for nearly it's entire existence. Originally it was named as a new species of Struthiomimus, and later given it's own genus by Russell in his review of the ornithomimids of Alberta. One of his chief characters for distinguishing this taxon was the ratio of tibia to femur length. This has proven very problematic as this ratio can be affected by individual variation and/or growth stage and subsequently Dromiceiomimus has been subsumed into Ornithomimus by various authors. Though the issue of whether it's synonymous with O. edmontonicus or a valid species within Ornithomimus is not agreed upon even by them. The most recent publication I could find was the Macdonald and Currie (2019) description of a near complete specimen. Therein they run a series of tests to see if the limb ratio is even a valid character, and to my surprise it seems to be so. Of the tested taxa (Dromiceiomimus, Ornithomimus, Struthiomimus, and Gallimimus) all kept a consistent ratio of tibia/femur length across absolute sizes, and therefore the ratio is independent of growth stage at least, suggesting that it could be a diagnostic character (Gallimimus is a small outlier, it had a slight negative allometry, the tibia shortened in comparison to the femur as the specimens got bigger). Combining this with subtle features of the hand and claws they reasoned that Dromiceiomimus was distinct at both the specific and generic levels.

As for depicting it, my best sources were the photos of the fossil from Macdonald and Currie (2018), the skeletal diagrams and thigh muscle reconstructions provided in Russel (1972), the "Ornithomimus brevitertius" skeleton in Paul (1989), and the image of the holotype pelvic girdle provided in Parks (1926). The integument of Ornithomimus has been fossilized in a couple specimens described in Zelenitsky et. al. (2012) and van der Reest, Wolfe, & Currie (2015). given the taxonomic issues, I figured the Ornithomimus integument would be appropriate. What surprised me about the integument was the wings. Specimen TMP 1995.110.1 preserves on its ulna carbonized traces of feather shafts. These traces disappear towards both the proximal and distal ends, meaning that the wing (pennibrachium of their terminology) would have been limited to the forearm and wouldn't continue onto the hand and 2nd finger, nor up to the shoulder as is the case in more derived maniraptors. It feels like a cardinal sin to depict dinosaur wings that way, but that's what the evidence shows for Ornithomimus at least.

The composition, colors, and pose were all inspired by Poodonkis (and if you get the reference maybe take something for your back pain). My challenge was to make him believably pink and spotted and to have him be 'snowed in.' I eventually settled on the idea that the bright pink would be male breeding plumage and since bullfinch, pine grosbeak, and pink headed fruit doves manage the color without filtering crustaceans like flamingoes or spoonbills I figured it could be justified. The spots could be either camouflage like a northern flicker or display like a peacock pheasant, so I done a little of both. The 'snowed in' was tougher, luckily there have been some determinations of paleoclimate for the Horseshoe Canyon Formation, most relevant here are the paleosol samples of Quinney et. al. (2013). Most of the specimens referred to Dromiceiomimus are from the Tolman Member of the formation, which was deposited in a cooler and drier interval. The mean annual temperature and precipitation determined by Quinney et. al. was comparable to those of modern Belgium and Luxembourg, which gives us a rough ballpark to play in. Close enough that I think a cold spring could reasonably produce a sleet storm, not quite a snow-in but close enough for the composition.

References:

Macdonald, I., Currie, P. J. (2018) Description of a partial Dromiceiomimus (Dinosauria: Theropoda) skeleton with comments on the validity of the genus. Canadian Journal of Earth Sciences 56: pg. 129-157. doi.org/10.1139/cjes-2018-0162

Russell, D. A. (1972) Ostrich Dinosaurs from the Late Cretaceous of Western Canada. Canadian Journal of Earth Sciences 9: pg. 375-402.

Paul, G. S. (1989) Predatory Dinosaurs of the World, Touchstone Simon & Schuster. pg. 391

Parks, W. A. (1926) Struthiomimus brevetertius - A new species of dinosaur from the Edmonton Formation of Alberta. Transactions of the Royal Society of Canada, series 3. 20(4), 65-70 (digitized, pg. 949-955)

Zelenitsky, D. K., et. al. (2012) Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. Science 338: pg. 510-514. DOI: 10.1126/science.1225376

van der Reest, A. J., Wolfe, A. P., Currie, P. J. (2015) A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation, Alberta, Canada. Cretaceous Research 58: pg. 108-117. doi.org/10.1016/j.cretres.2015.10.004

Quinney, A. et. al. (2013) Palaeoenvironmental and palaeoclimatic reconstruction of the Upper Cretaceous (late Campanian-early Maastrichtian) Horseshoe Canyon Formation, Alberta, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 371: pg. 26-44. doi.org/10.1016/j.palaeo.2012.12.009