Let’s get the most interesting part out of the way first. The holotype and only described specimen for the new oviraptorid Wulatelong gobiensis (Xu et al., 2013) preserves a nearly complete pes with a hyperextended second toe. This may be natural. If so, it is intriguing. So far, this has only been mentioned on blogs and popular media. I reported this when I first received the email and scanned the paper, noting first that Xu et al. illustrated the foot with an apparent hyperextended toe, and then did not mention it. Then Andrea Cau got in on the discussion on his blog, supporting the apparent morphology — which is visually compelling. And then Darren Naish tweeted on this, stressing the incredulity of the authors not to mention, even to dismiss, this preservation.
Posture of toes in “normal”-footed dinosaurs tend to have all the toes down near one another if they might be just normal; but in some specimens, this toe is splayed upwards of the others, and it has led some workers (especially Greg Paul, in 1988 and other places) to assume the toe was hyperextensible. Hyperextensibility in the foot may be predicted by the presence of several features: 1) a second metatarsal (MTII) that is much shorter than the fourth, on the other side of the weight-bearing toes; 2) the condyles of MTII that articulate with the second toe (pdII) are more ginglymoidal with a distinct groove dividing it into two condyles; 3) the non-ungual phalanges of pdII are relatively shorter than in pdIII, whereas they tend to be longer; 4) the distal end of pdII-1, the first phalanx of the second toe, is enlarged, and the condyles of the end may be inflected so that they oriented dorsally rather than distally; 5) the ungual, or claw, of the second toe (pdII-3u) is remarkably larger than would be predicted by pdIII-4u, the ungual of the fourth toe; 6) is strongly curved; 7) and has a larger flexor tubercle; as well as 8) the relatively even lengths of pdIII and pdIV while the distal ends of mt’s III and IV are even, as seen in troodontids and dromaeosaurids (pdIV is typically a little longer than pdIII, but is positioned closer to the ankle, which shortens it).
The holotype specimen of Wulatelong gobiensis (IVPP V18409) includes a nearly complete pes, shown above. This specimen shows evidence for characters 5 and 6, but the others cannot be determined (1–2, 4, 7) or are not present (3, 8), making the situation problematic enough that to assert an hyperextensible claw is to jump to conclusions. That, however, doesn’t make the pes morphology uninteresting.
In the next post, I will discuss the unusual morphology of the hand of IVPP V18409 and its import, especially the argument of its being a basal oviraptorine oviraptorid. I am leaving the discussion on the foot for now and will pick it up later, towards the end of a series of posts on this over the next week, so as to more fully discuss the nitty-gritty of characters of the foot, as that will help me discuss what the heck is going on with the foot above. Meanwhile, follow the comments below for more details.
Xu X., Tan Q.-w., Wang S., Sullivan, C., Hone, D. W. E., Han F.-l., Ma Q.-y., Tan L. & Xiao D. 2013. A new oviraptorid from the Upper Cretaceous of Nei Mongol, China, and its stratigraphic implications. Vertebrata PalAsiatica 51 (2): 85–101. [PDF]