Arrhinoceratops brachyops
(Re-upload because I forgot to sign it)
This is the first of a series of paintings I plan to do on the fauna of the Horseshoe Canyon Formation.
This image took me quite a while. There was a lot of digging and cross-referencing and swapping taxa. Originally I was inspired by a small farm pond near where I live, the pond scum, dead leaves, and dark branches looked like a good setting to plop a dinosaur into.
But which one? My go-to is always a ceratopsid because they're my favorites, and I'd been wanting to do some Horseshoe Canyon stuff for a while. So, the initial candidates were Pachyrhinosaurus (because it's my favorite) and Anchiceratops (because of the body fossil, more later). I decided against Pachyrhinosaurus as it's known from at least 3 separate monodominant bonebeds, one for each species within the genus, and at least 2 of those are floodwater accumulations. So, to me I think Pachyrhinosaurus + water would equal a wildebeest crossing the Mara composition, rather than a moose in a lake situation.
So I began on an Anchiceratops in the water.
But I couldn't leave well enough alone, I knew a little about the odd body fossil assigned to Anchiceratops and it's potential implications from an old TetZoo post (on TetZoo v2, which now no longer works properly so no images). So I went to digging and found that particular fossil got a proper description by Mallon and Holmes in the New Perspectives on Horned Dinosaurs book.
Side-note: This specimen is referred to in older works under the accession number NMC 8538 but in Mallon & Holmes (2010) it is referred to as CMN 8547. My best guess is that the designations got changed when the National Museum of Canada restructured itself into the Canadian Museum of Nature. I spent an entire day trying to find Lull's 1933 overview only for it to get a passing mention under the old number, but with a photo to confirm it was the same thing
Regardless, this fossil is a complete skeleton from the first to last vertebra, including every rib and every toe and every finger save for 2 hooves on the left hand. Unfortunately the skull is almost completely gone, only 4 fragments of the frill remain and they're barely enough to show it must've been a chasmosaurine. So, why was this touted as Anchiceratops for almost 100 years? In their description the authors make a compelling argument that Sternberg assigned it to Anchiceratops by default as he was likely unaware of any other ceratopsids from the Horseshoe Canyon Formation (Edmonton Formation at the time).
This body fossil is odd amongst ceratopsids for a couple reasons. normally ceratopsids are very conservative in their postcranial morphology, with the only notable differences manifesting as slight familial differences between centrosaurines and chasmosaurines, and differences due to different absolute sizes. CMN 8547 conversely has a few trait that ordinarily could be diagnostic, but without sufficient overlapping material (the head) it can't be directly compared to any of the chasmosaurines within the Horseshoe Canyon Formation. These include 2 extra sacral vertebrae, 1 extra dorsal vertebra, and 1 extra cervical vertebra. That extra cervical is particularly interesting because it's part of the syncervical, a uniquely ceratopsid structure composed of the first 3 (in this case 4) neck vertebrae fused together to hold the weight of their massive heads. The ribs are very thick for its size and additionally the olecranon process of the ulna is large and the deltopectoral crest of the humerus is HUGE. Taken together these traits have been interpreted as possible indicators of semi-aquatic habits; a Mesozoic hippo!
But who is it!? I'm painting a very specific body fossil, standing in the water where it's less than visible, and it's a ceratopsid. It needs a head! Another specimen is mentioned in the Discussion section of the description that preserves a skull and left forelimb, ROM 1493. This specimen, they report, had been previously assigned to Arrhinoceratops and later to Torosaurus. Torosaurus? that's an odd dinosaur to show up at this time and place, so I checked their citation on that; Farke (2007) in a different book on my shelf! There is no ROM 1493 mentioned, but ROM 1439 is! It's only mentioned in passing, basically stating that 'a thin frill is not enough to diagnose fragmentary fossils.' The mention is not suggesting this mystery overlapping specimen is actually Torosaurus. So I checked the Arrhinoceratops citation, Tyson (1981), which was also mentioned within the Torosaurus paper. In that paper this second Arrhinoceratops specimen is mentioned right near the beginning and is labelled as ROM 1439. So Mallon and Holmes made a typo. Further, Tyson states that at the time of her study ROM 1439 is both not fully prepared and its location unknown.
I done a Hail Mary and google searched ROM 1439. Lo, and behold! that specimen was both found and prepped, and then described in 2014! It has a badly crushed skull, partial neck and most of the left arm. Of the overlap with CMN 8547 the two important elements are the syncervical and the humerus (the ulna is not preserved in ROM 1439). The humerus does have the huge deltopectoral crest, but what is left of the syncervical is composed of only 3 vertebrae. Still not helpful.
I'd gone about as far as the fossils could take me, it was time to make a judgement call. I reckoned that the large deltopectoral crest was a unique defining trait that I could use to justify the pairing. The syncervical mis-match could be due to the poor state of preservation of ROM 1439, so maybe. This leaves Arrhinoceratops as a very tenuous identification for the body fossil, and while this is a super shaky referral, it's better than Anchiceratops which from what I could find has no known postcranial material; several skulls, but no bodies. Therefore, I continued on with my painting!
Below is my master process file from after my taxonomic super sleuthing spree.
I got a little wrapped up in the dinosaur and lost the focus on the environment I originally started with, but I do like how it turned out.
More Horseshoe Canyon to come!
References:
The body fossil CMN 8547:
Mallon, J. C., Holmes, R. (2010) Description of a Complete and Fully Articulated Chasmosaurine Postcranium Previously Assigned to Anchiceratops (Dinosauria: Ceratopsia) in M. J. Ryan, B. J. Chinnery-Allgeier, & D. A. Eberth (eds.) New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, pg. 189-202. Bloomington; Indiana University Press
The Torosaurus 'identification"
Farke, A. A. (2007) Cranial Osteology and Phylogenetic Relationships of the Chasmosaurine Ceratopsid Torosaurus latus. in K. Carpenter (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs, pg. 235-257. Bloomington: Indiana University Press
The Arrhinoceratops mention
Tyson, H. (1981) The Structure and Relationships of the Horned Dinosaur Arrhinoceratops parks (Ornithischia: Ceratopsidae). Canadian Journal of Earth Sciences 18: pg. 1241-1247
The Arrhinoceratops second specimen
Mallon, J. C. et. al. (2014) New Information on the rare Horned Dinosaur Arrhinoceratops brachyops (Ornithischia: Ceratopsidae) from the Upper Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences 51: pg. 618-634