The Changeling – The Foot

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.

Wulatelong gobiensis holotype pes

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 (12, 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]

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17 Responses to The Changeling – The Foot

  1. Andrea Cau says:

    Wulatelong may indicate that absence of osteological correlates of hyperextension is not absence of functional hyperextension.
    I’ve evaluated such in my blog, arguing that the derived condition in basal paravians (presence of both osteological correlates and evidence of hyperextension in articulated specimens) may derive from a more widespread ‘Wulatelong-like’ condition (absence of the former absent, presence of the latter). What hyperextends is a complex of soft tissues, not bones, the latter allowing a more extendive degree of hyperextension, but not the mere function. This may suggest an evolutionary precursor of the deinonychosaurian feature and an intermediate stage between absence of any hyperextension and the paravian condition.

    • Yes, I understand these points. However, the morphological corellate is the only real way we can argued this, especially when people like Greg Paul and Scott Hartman reconstruct Archie with a hyperextended mdII, despite the unequivocal preservation of this toe aligned with mdIII. If the reasoning is flesh alone, when we’d not have much way to evaluate it. I suspect the tendency to argue for hyperextension is based on preservation.

      There will be a follow-up post concluding the arguments when I get through my prepared discussion. But one of the data points, the enlarged ungual as evidence for hyperextensibility is equivocal as the proportion of the toe unguals is close to the condition in Khaan mckennai. I will go into more detail on this in the next post, which is mostly written.

  2. Andrea Cau says:

    Also, note that your list of features supports this interpretation: Wulatelong shows at least 2 of the seven features, thus is itself an intermediate between absence (0) and full development (7).

  3. Nick says:

    Is this a reasonable assessment? The proximal phalange (pdII-1) does not appear to be present, I do not think we can assume this is a natural articulation.

    • Nick says:

      That said, I am more annoyed by the authors’ choice in using II-IV designations to describe manual digit anatomy.

    • There’s more to this; there’s data in the OTHER toes that I wanted to present in the conclusion, when I talk about the proportions of the toes in more depth. For example, the toe proportions of pdIII and IV, their relatively morphology, etc. The presence of the second toe features in Avimimus portentosus and its much more clearly non-extensible morphology suggests that those toe features are not analogouys to extensibility. I sorta just wanted this post to introduce the subject, rather than fully discuss it. Well, aside from the comments!

    • Andrea Cau says:

      Note that also the distal end of Mt-II is missing. Perhaps, these parts were eroded away very recently, but the rest of the skeleton seems in natural articulation.

      • But toes get mixed up. Most interesting case for this is the third manual digit in Archie: It tends to be preserved crossing the second in a LOT of specimens, but it’s NOT natural. But since we’re missing not just the distal end of MTII but also all of pdII-1, as Nick notes, this seems a case for questioning the value of the preserved orientation. This is why it is better to look at morphology, and that is far more ambiguous.

        • Andrea Cau says:

          What if pdII-1 is currently preserved but still covered by matrix and/or pdIII-1?

          • I make the assumption it can exist and is the same length as pdII-2 — at least. But even if it were, and not longer than pdII-2 as in all other theropods, we don’t know if it were. Missing distal end of MTII may suggest we shouldn’t expect it. Playin’ it safe.

  4. df says:

    mmm… do you really think the pedal D-II is hyperextended? D-III and D-IV look to be mildly flexed to me, and D-II looks only slightly extended: no more extended than you would expect for a normal walking position.

    • It is my general hypothesis that the pes shows no evidence for extension, just preserved posture. Examined against the morphological data, it is not satisfying, but that is not saying it isn’t true. This skeletal reconstruction is done in the “safe” non-extended posture, and I’m rather fond of this reconstruction over the other.

  5. Pingback: The Changeling – The Hand | The Bite Stuff

  6. Pingback: The Changeling – The Skull | The Bite Stuff

  7. Pingback: The Changeling – The Analysis | The Bite Stuff

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