Memo Koseman Chides Me With Turtles, and Other Musings

So today, after spending a relaxing yesterday working on two unrelated projects (one of which was the subject of this comment-heavy post on my hypothesis on oviraptorid diet), Memo Koseman (or NemoRamjet, of DeviantArt, who is a fantastic artist, by the way) decided to take me to task for my recent posts on ornithischian soft-tissues (this one, and this one, which follow this one, which frames my initial hypothesis).

Memo posted the following “meme” picture:

That’s the alligator snapping turtle (Cryptodira, Macroclemmys temminckii) up top, and African [or Nile] soft-shell turtle (also Cryptodira Pleurodira, Trionyx triunguis) below.

Tagged with this, was Memo’s comment, referring to my recent posts:

My opinion on the “cheekless dinosaur world” hypothesis proposed by Jaime Headden. I think that lips, cheeks and beaks can show far more variety in a single clade than normally assumed.

The point that irks me, and it irks Dr. Casey Holliday as well — whose work I have heavily cited as it is been intrinsic in assessing homology and analogy in soft tissue reconstruction for fossil animals — is the use of “extant phylogenetic bracket.” This refers to the post that started it all, “Making Lip of It,” in which I attempted to use the EPB as a tool to determine what kind of extraoral tissues would be present in theropods. This seemed like an easy thing, and so far no one had questioned whether theropods would have realistically had cheeks, not Velociraptor mongoliensis anyway, and so I figured I was on stable ground. Moreover, I did not rely on the EPB to make my case. In fact, if I were to restrict myself to the EPB, we would find me arguing against any sort of fleshy extremity. I extended the bracket, but moreover, I referred to work by Drs. Tobin Hieronymous and Larry Witmer, who following the former’s doctoral dissertation work, were trying to figure out not just sauropsid soft-tissue correlates on bones of the skull, but also in theropsid, the side of Amniota that includes mammals.

I realize, however, that I haven’t been very noticeably explicit in my regard to the data I’ve presented. I’ve claimed this as an “argument,” qualified based on various factors, including “[d]irect tissue homologies, extrapolation of the extant phylogenetic bracket, and functional considerations of the jaws should,” where I qualify the data when dealing with fossils, and then I note “only in the gaps this information doesn’t cover should speculation enter the framework.” I then present one such specific refutation, Panoplosaurus mirus.

I do not believe I am correct; I think the fossils are, however, but we all make assumptions on how we handle them, and consider their nature as living organisms. We don’t have all the data, but we try to find it. One way in which data gets obscured is when people make broad statements, saying a thing “must” be (“ornithischians must have cheeks”) or that they “can’t” be (“we can’t know everything, so it’s okay just to broadly generalize; no need to explicit support”). I’ve been delving into the specifics of this for some time, and know myself I don’t have all the answers, nor do I think I can truly argue the right way. But this entire series of posts is based on hypothesis, produced by applying assumptions to a leading premise:

What is the soft-tissue structure around of the mouth of X?

I have been less than clear than I could be in noting that variation can exist, where I’ve discussed with particulars in places other than this blog, but especially in the post that certainly sparked Memo’s response and a veritable “explosion” on FaceBook, I wrote [scroll towards the end]:

There are, of course, possibilities (I say, waffling) that some ornithischians had developed a fleshy “cheek,” almost certainly one not comprised of muscle, while others did not. Ornithischia is a complex clade, and its backbone was a series of lineages all based on small, bipedal taxa with jaws full of teeth and no real distinct inset of the jaws that might even suggest a “cheek,” yet has produced three clades all convergent on the lingually-rotated mandibular ramus[.]

Wow. It’s like I am saying that there is no one answer. I haven’t been as explicit in this, even though I have included cautionary language in regards to the conclusions I make on the bases of the data I present and allude to. I do not have all the data, and I also do not mention or refer to unpublished or personal data, merely my own observations from shown data and from the literature. I do not think it untenable to post on this before this work is “available,” seemingly premature or not. I am explicitly attempting to determine where the limits of specific data lie.

Let me put it this way: I cannot say what the form of the flesh that surrounds the mouth of a fossil carnivoran mammal was, whether it was a rostrally-extended fleshy, nonmuscular cheek formed from the rictus, or if there were giant bloodhound like flaps of the lips, or something like the distended flap on cat lower lips, and so forth, with any level of certainty. I can make inferences, certainly. I don’t have a process by which I can determine the presence of flanges of skin sticking off the sides of the head in mata mata (Chelus fimbriatus), or the fleshy flaps that hang down and cover the beaky rhamphotheca in trionychids, shown at top and used as evidence for “cheeks” in turtles. But I can try to use certain tools (as mentioned) and make inferences of the first and second type to see what is likely, and test against that. My posts are merely that: speculation, with some attempt at grounding.

I should also note that it has been the unifying premise of my posts on this topic that I have been using these tools to deduce the presence of extra-oral tissues, not their absence. It is not my desire to prove a negative.

Then again, it is also probably wrong of me to make “conclusions” in regard to this: There likely will, eventually, be a hard and fast answer on what tissue is associated with what fossil, and simple things we can point to that say “that’s why.” We’re not there yet.

Incidentally, my initial argument I was going for in “Making Lip of It” was that theropod dinosaurs had NO fleshy “lips.” It eventually went the other way as I realized the data could not reasonably support that conclusion based almost strictly from comparison of soft tissues: theropods like Velociraptor mongoliensis seem to lack features that appear in turtles and birds — the taxa I used to consider rhamphotheca — and nor they have have croc-like cornified skin, which left me with squamates, and I couldn’t find a reasonable case where anything other than say a few bits of cornification of the rostral tips of the jaws might occur, but not evidence supporting a “beak” or bone-tight skin. Color me surprised.