Recall my earlier post on Daemonosaurus chauliodus. At the time, I thought this was a pretty silly dinosaur to provide a reconstruction for, since for the most part I agreed with the authors’ reconstruction, it matched the skull as i saw it, and their own interpretations. There are some issues, but those issues are minor, but broadly noticeable and thus something that can be accounted for relatively easily. First, the reconstruction from Sues et al.:
One of the more noticeable features of the skull is the oddly juvenile aspect: the overly large orbital fenestra, and short snout, the short triangular aspect of the snout, and the giant, snaggly teeth. It’s those teeth I’m interested in, and in many cases, find that extraordinarily-elongated teeth in conventionally-shaped skulls are worthy of heightened scrutiny. That is to say, it seems unusual, but one shouldn’t accept it and it bears further investigation.
Elongated teeth usually arise through either natural recovery, when the teeth have exceptionally large crowns, or exceptionally long roots (when the tooth is thecodont, found within a deep socket surrounded by bone), or because the tooth as partially become dislodged within its socket, which can arise due to replacement teeth lying underneath and pushing outward, or because the soft-tissues that bind the root to its socket have been degraded. These loose teeth can look exceptional, and have occasionally resulted in being described as a natural feature of the skull in question, and even feature in fleshy reconstructions of the belonging skull. A great example is in a juvenile Ceratosaurus ?nasicornis, in which the teeth seem to overhang the mandible when the jaw is shut. This reconstruction may actually put the lie to the hypothesis for an enclosing, squamate-like fleshy “lip,” but if the teeth are slipped from their sockets, and hanging by a thread of tissue when the skull was fossilized, then it seems more likely the skull is “conventionally toothed.
I suspect the same happened in the jaws of Daemonosaurus chauliodus, largely because the shape of the teeth themselves show a distinct caudal recurvature and basal expansion of the distal carina but in the mandibular teeth and some teeth of the upper jaw, these seems to end halfway along the exposed crown. Almost certainly, this can be settled by examining extent of enamel, but also extent of soft-tissue to enamel exposure on crowns in living reptiles and/or mammals, and consider how extrapolable this is to dinosaurs. Part of this argument stems from an observation that generally (though not always) the upper dentition of a closed reptile’s jaws (including lizards and tuataras for the most part) tend not to pass beyond the line of foramina that follows the mandibular branch of the trigeminal nerve that innervates the lateral surface of the mandible. This nerve innervates the lateral tissues of the jaw, including the oral margin and sensory organs that lie around the jaw surface, including in crocodilians and mammals, and innervate the “lips” in mammals, lizards and snakes alike, but is also found in birds, which do also possess foramina tracts that follow the trigeminal nerve; they would, by logical extrapolation from the EPB, do so in theropod dinosaurs as well. I find it generally unlikely that this tract would exhibit tissues flush to the jaw’s outer wall, show no evidence of this in the form of impressions on the jaw surface for blood vessels typically associated with close-lying hard tissues such as cornified keratin sheaths, as this is the only process by which the jaws can have a sensory surface, but the teeth overlie them. I pointed out this improbability here. It is an hypothesis, then, that teeth should not generally extend far beyond the mandibular foraminal tract, and that this tract represents a general boundary for the base of the lower extraoral tissues where they separate from the mandible, forming a “trough” lined with epithelium into which the upper teeth are contained. Rather than see snaggly-toothed theropods, the teeth should be kept “pocketed” as they are in lizards and snakes and most likely most non-eusuchian crurotarsans. I’m beginning to wonder if the same is true for sauropterygians (ichthyosaurs, plesiosaurus) and other reptiles as well (e.g., placodonts) often shown with teeth fully exposed when the jaw is shut, though those groups and various others haven’t received much scrutiny on facial reconstruction.
Nonetheless, this forms the basis of a more “conservative” cranial reconstruction for Daemonosaurus chauliodus, which also alters how Sues et al. restored the postorbital skull, which was damaged.
Sues, H.-D., Nesbitt, S. J., Berman, D. S. & Henrici, A. C. 2012. A late-surviving basal theropod dinosaur from the latest triassic of North America. Proceedings of the Royal Society of London, B 278:3459-3464.