We're really in the dog days of summer up here in Toronto (remind me not to move somewhere with humid summers for my next job), so I'm putting a spin on this for the next couple weeks with a series I'm calling "The Dog Days of Dissorophids," where I talk about my actual dissertation study system for once instead of waxing poetic about metoposaurids. This may or may not be foreshadowing an in press publication as well...
A brief history of Cacops
Cacops is a fairly old (in a historical sense) dissorophid, particularly for North America. It was described in 1910 by the American palaeontologist Samuel W. Williston in a paper creatively titled "Cacops, Desmospondylus; new genera of Permian vertebrates" ("Desmospondylus" was some form of reptile that was almost immediately recognized to be the same animal as the already described stem amniote Seymouria the following year). The first species was Cacops aspidephorus, named from a dense bonebed from the early Permian of Texas that was aptly named the Cacops Bonebed. You can find the skeleton of this animal on display at the Field Museum in Chicago alongside other early Permian temnospondyls. For 99 years, this was the only known species of Cacops (not that unusual). Then in 2009, a second species from the early Permian Richards Spur locality in Oklahoma was named by my advisor, Robert R. Reisz, Canadian palaeontologist Jason Anderson (University of Calgary), and German palaeontologist Rainer Schoch (Staatliches Museum für Naturkunde Stuttgart): Cacops morrisi. A third species was named in 2012, also from Richards Spur, by German palaeontologist Nadia Fröbisch (Museum für Naturkunde) and Robert: Cacops woehri.
How do you pronounce that name?
I'm honestly not sure - I hear both 'cake-ops' and 'cak-ops.' I'm sure someone who reads this blog will know based on the purported etymology of the name ('blind face').
What makes Cacops special?
There's a lot of dissorophids, so many of them are distinguished by unique combinations of fairly esoteric anatomical features, rather than a large number of singular unique features (autapomorphies). All species of Cacops have long skulls, with the back end being proportionately short. They have a pretty large otic notch (where the ear would have been) with a fairly unique architecture. Their osteoderms are short anteroposteriorly (front-back) and transversely (side-to-side).
One other attribute (not diagnostic but special) is that we know of quite a lot of Cacops material. As the name suggests, the Cacops Bonebed was extremely productive, although it is unfortunately now underwater due to artificial damming of Lake Kemp, and there is only one other published specimen of Cacops aspidephorus not from that locality, so the future prospects in Texas seem rather slim... The Richards Spur site has continued to produce on the other hand. Fragmentary remains were first identified at the site by the late American palaeontologist John Bolt (e.g., Bolt, 1977) and later by Robert and Canadian palaeontologist Corwin Sullivan (Sullivan et al., 2000), but there was nothing that suggested that it was a different species from C. aspidephorus. Fast forward to today, and we're up to five complete skulls of Cacops morrisi and about 0.75 skulls worth of Cacops woehri (half of one skull and a back end of another) (Reisz et al., 2009; Fröbisch & Reisz, 2012; Fröbisch et al., 2015). Considering that many dissorophids are known from a holotype skull and maybe one or two more fragmentary specimens, this is pretty substantial! Why does having a lot matter? It gives palaeontologists a better idea of variation, for example that which occurs during development of the animal. If you only have one, and the animal is long-dead, you can't exactly make many inferences about how it grew. We have a bunch of variably sized Cacops that help us characterize growth and thus use it as a reference for other dissorophids that might have had similar development but that don't have enough specimens at the moment to know.
A tale of two dissorophids
When I moved to Canada, one of the first things I started working on was this pair of blocks, each with a complete skull of Cacops morrisi. One was articulated with the front half of the body, and the other had a nearly complete backbone lying on top of it. This was some of my first exposure to the Richards Spur locality, and these specimens were AMAZING. I spent the first couple months of my PhD studying these (in parallel with metoposaurid projects of course), during the course of which I did a little bit of prep on each of them. Lo and behold, there was actually more Cacops in each block. The first block (we'll call it block A) with the articulated skeleton had a snout on it, and the second block (block B) with the full backbone had part of a postorbital (behind the eye) region. Cool, no problem, add it into the description. It was late one night (like 8 PM, so not that late, but the sun sets at 5 in March up here, so it was uncomfortably dark outside), and I was putting together the last touches on my manuscript. I wrote the sentence, "block A has a complete skull and a partial skull with the pre-orbital region, and block B has a complete skull and a partial skull with the postorbital region." My thoughts then proceeded in the following fashion:
I honestly thought this was some kind of set up - that everybody else had known all along that these blocks fit together and it was some weird test to see whether I could put it together (literally and figuratively). It was not apparently The punchline? Robert got those blocks from different people, and he didn't know they fit together either! Although the fit is tight between blocks (i.e. there wasn't a lot lost on the edges of the blocks), it was only with the exposure of the skull that's broken in half between the two blocks that there was a clear connection; there wasn't really much other fossil spanning the break that would have keyed us into these blocks fitting together. Again, they had distinct specimen numbers too, which usually I've not questioned the reliability of...
Given all of this, the next day, we pulled out all of the large blocks we had from Richards Spur and tried to jigsaw them together. We ended up finding one more fit that comprised a large headless non-Cacops dissorophid, again made of two blocks with different specimen numbers and that came from different people! You can read about that specimen (which also has a Cacops butt preserved on it) in Gee & Reisz (2018b in Fossil Record).
About the blog
A blog on all things temnospondyl written by someone who spends too much time thinking about them. Covers all aspects of temnospondyl paleobiology and ongoing research (not just mine).