New publication: Dissorophid diversity at the early Permian cave system near Richards Spur, Oklahoma (Gee, Bevitt, & Reisz, 2019; Palaeontologica Electronica)

Title: Dissorophid diversity at the early Permian cave system near Richards Spur, Oklahoma.
Authors: B.M. Gee, J.J. Bevitt, R.R. Reisz
Journal: Palaeontologia Electronica, article 22.2.46
Link to paper - this is an open access paper than anyone can read!

Summary for non-scientists
​Despite the above image including a lot of CT data, this is not really a CT paper. It is, however, a metaphorical smorgasbord of dissorophids - 21 specimens reported for the first time here, distributed across at least 4 genera, all from Richards Spur. Dissorophids are the ones with armour along their backbone, which you can see in the above image (os.i = internal osteoderm). We've got new skulls, new skeletons, and new data! The point of this paper is largely to summarize what we know and what we have from  the locality, which is quite a lot (coincidentally we've got even more in the last few months since this paper was accepted). This plethora of new specimens gives us a lot of new anatomical information, including internal data that we gleaned from the CT data, and also expands the known diversity at Richards Spur by an additional two taxa that were previously only known from Texas.

​Even more Cacops​...
​I think we find a new Cacops specimen every year that I've been here. The skull of Cacops morrisi with associated postcrania from the anterior part of the skeleton (below on left) is the sixth that we've published on (fourth for me) and the seventh in existence. Normally, it would be a pretty remarkable specimen in terms of completeness and the presence of articulated postcrania, but a comparably sized specimen that we previously published on (Gee & Reisz, 2018a; JVP) is even better preserved than this one, so it doesn't contribute as much new information as you might think. The Cacops woehri skull (below on right) is the third published one and somehow got perfectly sheared straight down the midline. I looked for that other half, but it might very well be 2" farther down (the block is about 6" thick), and there was too much other stuff that would have to be destroyed to even explore. This specimen is distinctly larger than the holotype (which is split in a similar fashion) and about the same size as the second specimen (which was just the back of the skull).

New Cacops morrisi specimen.

New Cacops woehri specimen.

​Williston's mystery humerus
In one of my previous publications (Gee & Reisz, 2018b; Fossil Record), we described a headless dissorophid from Richards Spur that was very clearly not like any other dissorophoid from the site (we knew of more or less all of this newly published material too). However, it looked a lot like this one that American paleontologist S.W. Williston figured in 1910! Unfortunately, Williston didn't describe it much other than to say that it was a new species, and he didn't list a specimen number. I always suspected it was at the Field Museum where the bulk of the other described material is reposited, but it's kind of hard to track down one specimen when you don't have its number or much idea of its taxonomy. 

Me comparing Williston's mystery humerus to the one that we published on from Richards Spur (Gee & Reisz, 2018b).

​So conveniently, about a month after the paper was published, I was at the Field Museum and found Williston's specimen! Of course, it was sitting in one of those drawers way high up that stored random miscellaneous amphibian and reptile bits. Above you can see the photo of me holding the specimen up against the image of the Richards Spur animal. Unfortunately, nobody else has a precise idea of what the animal is either, so the precise taxonomy remains a mystery... We found a few more fragments that we think go to this animal from Richards Spur, so the Field Museum specimen is also included in there as a supplement. 

Illustrations of the mystery humerus from Williston (1910).

Photos the same humerus from this paper (Appendix 4).

Digital slices through osteoderms of Cacops and cf. Aspidosaurus, showing the internal relationship of the osteoderms with the neural spines.

​New insights into osteoderms
Osteoderms are a typical feature of dissorophids, although they are found in many other flavours in other temnospondyls. In dissorophids, the osteoderms are thought to have stabilized the trunk during terrestrial locomotion (Dilkes & Brown, 2007; Dilkes, 2009) and are thus not the same as osteoderms that might confer protection against predators (see ankylosaur dinosaurs, for example). 
    Osteoderms come in a lot of shapes and forms within dissorophids, with general patterns. For example, derived eucacopines such as Cacops have two series of osteoderms. The internal series fuses to the vertebral spines in adults, and the external series has a ventral flange that inserts between successive internal osteoderms. Here, we (largely inadvertently) identified a ventral flange (abbreviation: 'vf') on the internal series as well (see 4-6 to the upper left). This is interesting because ventral flanges on internal osteoderms is only supposed to occur in dissorophines such as Dissorophus ​(see below). 

Digital segmentation of osteoderms of Dissorophus showing the internal anatomy of the ventral flanges and the association with the neural spines.

Furthermore, only dissorophines and derived eucacopines are supposed to have two series of osteoderms. This has led previous authors to conclude that the double series evolved independently in both of these dissorophid subfamilies (Schoch, 2012), which would explain the various differences between the osteoderms of these two groups. However, we also identified what appears to be a very clear double series in what is supposed to be an early diverging (basal / 'primitive') dissorophid, Aspidosaurus (see 1-3 in the first figure of this section). Compared to dissorophines and eucacopines, the internal osteoderm is disproportionately smaller than the external osteoderm and largely covered by it. This raises a lot of questions about whether this really is Aspidosaurus (by all other accounts it's indistinguishable from other Aspidosaurus ​material), in which case it could be that the double series wasn't identified by previous authors for any number of reasons (or doesn't occur in everything assigned to Aspidosaurus, or only occurs in part of the vertebral column, or....well there are lots of options) or if it is something very close to Aspidosaurus but not Aspidosaurus proper. Part of the problem here is that the type species of Aspidosaurus was only known from the holotype, and that was destroyed in World War II... 

Photos and digital segmentation of isolated osteoderms and neural spines that we *think* go to Aspidosaurus.

I also got a sweet tattoo out of one of the specimens we described for this paper (no I didn't get it just because it was a temnospondyl). The ink was done by E.K. Chan, who is a phenomenal person and artist; you can see the illustration they did for me to the left and check out their Instagram page here!

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TLDR: Lot of new dissorophid material from Richards Spur - (1) additional anatomical details that further inform on the taxonomy of previously known taxa; (2) new reports of taxa previously known only from other sites; (3) sweet CT data; (4) tattoo for Bryan.

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Refs

• Dilkes DW. 2009. Comparison and biomechanical interpretations of the vertebrae and osteoderms of Cacops aspidephorus and Dissorophus multicinctus (Temnospondyli, Dissorophidae). Journal of Vertebrate Paleontology, 29(4):1013-1021. doi: 10.1671/039.029.0410
• Dilkes D, Brown LE. 2007. Biomechanics of the vertebrae and associated osteoderms of the Early Permian amphibian Cacops aspidephorus. Journal of Zoology, 271(4):396-407. doi: 10.1111/j.1469-7998.2006.00221.x
• Gee BM, Reisz RR. 2018a. Cranial and postcranial anatomy of Cacops morrisi, a eucacopine dissorophid from the early Permian of Oklahoma. Journal of Vertebrate Paleontology, 38(2):e1433186. doi: 10.1080/02724634.2018.1433186
• Gee BM, Reisz RR. 2018b. Postcrania of large dissorophid temnospondyls from Richards Spur, Oklahoma. Fossil Record, 21(1):79-91. doi: 10.5194/fr-21-79-2018
• Schoch RR. 2012. Character distribution and phylogeny of the dissorophid temnospondyls. Fossil Record, 15(2):121-137. doi: 10.1002/mmng.201200010
• Williston SW. 1910. Cacops, Desmospondylus; new genera of Permian vertebrates. Bulletin of the Geological Society of America, 21(1):249-284. doi: 10.1130/GSAB-21-249