Here’s the skull of the anurognathid Anurognathus ammoni. This guy appears on the banner above — occasionally — to which I’ve granted nice, long filamentous integument, especially in front of the eyes. And there’s not a whole lot in front of the eyes….
Since Döderlein’s original description, there have been only two serious attempts published to reason out the cranial anatomy and arrangement of bones of the holotype’s skull, crushed and scattered. The first, Wellnhofer’s 1975 treatment in a review of Rhamphorhynchoidea (paraphyletic version), helped establish the “very short skull” of this animal, a novelty among the slender, triangular skulls of all its relatives. The second, Bennett’s 2007 description of a second, smaller specimen which included a much, much more complete skull, has cemented the reconstruction of a face dominated by the orbit.
The head of Anurognathus ammoni is half orbit, one-quarter eyeball.
So, those are pretty huge eyes. And here I thought oviraptorids probably had big ones. But the more interesting thing is that for their size, the scleral ring seems fairly thin. I haven’t done the math, but it does seem to suggest that Schmitz & Motani’s (2011) hypothesis about relative diameters to active foraging time (or diel) indicates that Anurognathus ammoni had scotopic eyes, and was thus likely nocturnal. A further analysis, by Thomas et al. (2006), indicates that — for shorebirds, at least — mere eyeball size and proportions indicates diel, but that foraging with tactile capabilities does not affect eye size, nor is such behavior predicted from eye size. As it is, whether these pterosaurs used long filamentous “whiskers” as do nightjars is something of a untested hypothesis. I reconstructed the silhouette for this pterosaur, as will be visible in the banner (happy hunting!), to have enormous filaments sprouting rostral to the orbit, something the fossils do NOT indicate.
Aside from the bones of the skull, the eyes were probably the heaviest part of the head, and one might think that with such investment, there might be little else in the head to really devote a lot of energy developing — eyes are expensive organs! Thus, with a plate reduced to thin struts (not very visible in these images), a braincase smaller than the volume of one eye, and thin, fragile teeth in a jaw quite unlikely to be fused, I tend to think these animals may not have spent a whole lot of energy actually processing their prey in their mouths. It seems more likely that, as do frogmouths, nightjars and many, many microbats, this little pterosaur would have hunted on the wing, and caught and swallowed prey as whole as possible. It is also for this reason that I’ve forgone the typical interlocking rostral dentition, which almost everyone else tends to include, and simply pulled the lower teeth inside the uppers; really, it probably didn’t need to interlock teeth, as these animals were likely not holding on to prey in their mouths. Grab and swallow.
Bennett, S. C. 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81: 376-398.
Döderlein, L. 1923. Anurognathus Ammoni, ein neuer Flugsaurier [Anurognathus ammoni, a new pterosaur]. Sitzungsberichte der Mathematisch-Naturwissenschaftlichen Abteilung der Bayerischen Akademie der Wissenschaften zu München 1923: 306-307.
Schmitz, L. & Motani, R. 2011. Nocturnality in dinosaurs inferred from scleral ring and orbit morphology. Science 332: 705-708. (SOM) [Note: This paper received a reply, to which the authors in turn replied]
Thomas, S. J., Székely, T., Powell, R. F. & Cuthill, I. C. 2006. Eye size, foraging methods and the timing of foraging in shorebirds. Functional Ecology 20: 157-165.
Wellnhofer, P. 1975. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Teil I. Allgemeine Skelettmorphologie [Rhamphorhynchoidea (Pterosauria) from the Upper Jurassic limestones of southern Germany. Part I. General morphology of the skeleton]. Paläontographica, Abteilung A 148: 1-33.
Sorry to hear you bought into Bennett’s little monster. No other anurognathid has these skull proportions. All have smaller eyes in the back of the skull, like all pterosaurs. All have a larger antorbital fenestra than orbit. No other pterosaur has that ultra-wide, set of parietals, greatly separating the upper temporal fenestra apart from each other. Bennett’s main mistake was identifying a maxilla with tooth root subdivisions for a giant scleral ring preserved edge on, which never happens otherwise in crushed fossils. Despite the complete skull, Bennett, by his own admission, was unable to identify many bones and unable to find paired bones, other than those of the skull roof, which don’t fit ptero morpho patterns. The real smaller scleral rings near the back of the skull are like little cheerios and every other paired bone, including the other maxilla, are identified in a layered movie at reptileevolution.com/anurognathus-SMNS.htm. All the bones can be lifted without distortion and placed into a reconstruction in which all the parts fit, and closely follow the shapes of other anurognathids, further validating the flat-head reconstruction.
1. I’m not so sure all the anurognathids have the same cranial structure, or should. They may be paraphyletic with respect to most other pterosaurs. Inference from other taxa is fine, as long as you allow yourself to look at other taxa, not just those you assume to be relevant. But even so, there are differences in the cranial structure of anurognathids that makes copy-pasting problematic; this works with those odd ducks, scansoriopterygids, too, which have some similar cranial morphology, skulls that resemble megalancosaurs and anurognathids in many respect, but which appear to have vastly different oral anatomy. Not a problem: They can be scansoriopterygids, too.
2. Anurognathids in the broad sense (that is, including all taxa referred to the clade) may have fundamentally different cranial structure as befits animals that can specialize on a variety of prey. Some taxa may specialize on insects, some have giant eyes and a nocturnal diel, some were probably diurnal, and had tinier eyes. These can influence wing shape, claw curvature, body size and proportions. Anurognathid cranial form may be diverse, but it is also highly specialized; it is NOT surprising to me that so many different reconstructions have been produced for them, but most have settled on the broad, rounded snouts, and indeed the structure of the skull heavily implies a very broad head, short face, very forward-facing eyes, and an overly-baord temporal region of the skull. Not shown is that I ALSO produce a dorsal skull reconstruction, and will produce a ventral. These reconstructions take into account several things, but not least of which is that in many ways, there may be cartilaginous elements of the skull that simply do not preserve, and portions of the palate and temporal region may be among them; this reconstruction makes broad assumptions on identifications, but it does so by first taken the VERY DIFFERENT palatal structure into account. There seem to be rules about how some bones associate with others, and application of these rules suggests that the skull looks a lot like this.
3. I do no “buy” into Bennett’s reconstruction, I used the material as the basis of the reconstruction. And given that I am not doing this based on the illusions of tracing artefacts on photos, I think you can cut me a little slack. It also happens to be an hypothesis, not a settled, agree-upon conclusion. This is A reconstruction, not THE reconstruction.
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I hear alot of “mays” here. You’re cutting Bennett a lot of slack. Bennett’s reconstruction breaks all the rules. If I had come up with that reconstruction you would have given me the same arguments I’m giving you. One of these days you’ll have to explain to me why my anurognathid “illusion” bone tracings are symmetrical, I find every bone and they precisely fit into in vivo reconstructions, and reconstructions match one another in morphology and follow phylogenetic patterns. Jaime, just look at the closest outgroup to anurognathids, Dimorphodon, and you’ll understand anurognathid skull morphology, only a little smaller, a little wider with small eyes in the back half of the skull and a big antorbital fenestra. If you don’t like that experiment find me just one more anurognathid with giant scleral rings in the front half of the skull. Just one more. Good luck.
Once again, please don’t assume I just take the paper’s arguments for granted, or dismiss your … err … reasoning for the sake of doing so. I do actually look into this myself. When citing this stuff, though, unless I can come up with better, I fall to the best previous reconstruction I can’t discount. My reconstruction does NOT copy-paste Bennett’s, there are personal observations involved in there. As for breaking rules, WHAT RULES?
Consider that “closest” outgroups for some pterosaurs vary from analysis to analysis: anurognathids shift from the most basal pterosaurs, more derived than eudimoprhodont-ish taxa, more derived than dimorphodont-ish taxa, or even more derived than rhamphorhynchid-ish (Rhamphorhynchoidea, sensu stricto: Rhamphorhynchus muensteri <- Pterodactylus kochi), from analysis to analysis. There are certain patterns that appear in many analyses, but this tends to involve character selection, and that’s the problem: There’s not an analysis out there that uses more than 200 characters, despite the range of morphology. Cranial characters dominate these, but mandibular or mandibular-inclusive characters have varied from less than 5% of the total character list, to barely more than 12%. Some have had NO mandibular only characters! Correct, and quantified, pterosaur character analysis has NOT been done, and until it is, I will not take any arguments of “outgroup”-based constraints for granted. Beyond that, If there is something about the skull that counterindicates an inference from an implied outgroup, then it stands to reason it isn’t a very good model for that point. I just went through a character by character analysis of purported similarity involving Scansoriopterygidae; had I taken the tact of simply pretending the shape by itself was valuable, and start interpreting elements by supposed sister taxon relationship, I would have come to different conclusions. Indeed, I could have performed additional analysis assuming sister taxa and assessing character polarity and possible distance between lineages; simply thinking about this, I would have LONGER distance between Scansoriopterygidae and Paraves, than with Oviraptorosauria, but shorter distance if, instead, I assumed a non-Ovi+Paraves position with Alvarezsauria or Ornithomimosauria relationship, as the origins for those clades come closer to the Middle Jurassic than Oviraptorosauria/Paraves.
I also have something of a thing for looking at cranial and facial shortening in taxa. There is no reason to assume this doesn’t occur in pterosaurs, as it does occur in squamates (as it does in snakes and several lineages of lizards), in turtles, in mammals, in stem-mammals, in various dinosaur and croc clades, and in birds specifically. The “rules” are generally universal: the transversely arrayed, higher than long premaxilla; “subvertical” ENF; and positively GIGANTIC orbit (as supported by the size of the scleral ring, which your reconstruction shrinks by under half) all support a strongly rostrocaudally-shorted skull and especially facial region. Assuming that the sister-relationship with dimorphodont-ish taxa is making you think the WHOLE skull must be organized and proportioned accordingly, and that means you’re not interpreting the skull through examination of the material itself. You seem to be putting too much weight in your characters (however sparse and undersampled they are), and haven’t produce enough data that helps correct sampling bias and observer bias. That’s why I’ve tried to get you to increase your character sampling, improve character analysis, test your “DGS” “method.”
And that’s a cute dare, Dave: I have to find a scleral ring. Not a giant orbit, such as the humongous length of the orbit in Jeholopterus ningchengensis — no, I have to specifically find a ring.
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