Deep Breath Now….


In all seriousness, though this joke never seems to get old with some people, Amy Balanoff and Dr. Mark Norell have just recently published the long, long — extremely long — awaited monograph on Khaan mckennai, stately oviraptorid without a cranial crest. The monograph deals with three specimens, the first two including the holotype (MPC-D 100/1127, missing most of the tail) and a referred nearly complete skeleton (MPC-D 100/1002), and a partial skeleton and nearly complete skull (MPC-D 100/973, which is dorsoventrally compressed).

Khaan mckennai mpc-d 100-973 skull

While the monograph leads off with color photos, such as the ones above and below, greyscale photos present the rest of the monograph, and are the only illustrations aside from a modified cladogram. Rather than use the later “MPC” label for specimens at the Mongolian Paleontological Center of Ulaanbaator, Balanoff & Norell follow general AMNH operating procedure by using the “IGM” label. MPC-D 100/973 is used for extensive CT sections, and reveals in part that the endocranial cavity is smaller relative to the skull than in Citipati osmolskae, while there are less extensive cavities within the frontal. I have some thoughts about that, but it seems notable that the frontal is relatively shorter in Khaan mckennai than in Citipati osmolskae.

Khaan mckennai skeletons

Skeletons of Khaan mckennai (Clark et al. 2001), MPC-D 100/1127 (holotype; left) and MPC-D 100/1002 (right).

Khaan_mckennai_skeleton2

Khaan mckennai is a gracile, small animal, illustrated above with a skull based on MPC-D 100/1002. It is also the best oviraptorid for which a cervical series is known, and as shown it is quite elongated by the presence of numerous small, relatively short vertebrae. (The skeleton is shown in a mere, “skin-wrapped” aspect. I’ve not had time to correct the fattening and integument of many skeletons; maybe some day.)

One short point before closing out: Balanoff & Norell remark on the often quite extensively fenestrated maxilla in oviraptorids. In some taxa, the lateral surface is penetrated by several large, elongated foramina which appear to correspond to the tract of the maxillary nerve and are ventral to the antorbital fossa; however, there have been some questions as to the problem of the maxillary and promaxillary fenestrae, which are entirely enclosed by the maxilla in most, if not all, theropod taxa. Balanoff & Norell argue that the large fenestra, conventionally referred to as the maxillary fenestra, is in fact a promaxillary fenestra, while the smaller fenestra often dorsal to it is the true maxillary fenestra. This is remarkably similar to the argument Mickey Mortimer made back in April of 2011 here, and a comparison is provided below:

Top section from Balanoff & Norell (2013); bottom after Mickey Mortimer. Slightly modified for the format. In the top section, red is the antorbital fenestra, blue the promaxillary fenestra, and green the maxillary fenestra; oviraptorids may present an additional, more ventral fenestra representing ventral extensions of the antorbital fenestra into the maxillary "body."

Top section from Balanoff & Norell (2013); bottom after Mickey Mortimer. Slightly modified for the format. In the top section, red is the antorbital fenestra, blue the promaxillary fenestra, and green the maxillary fenestra; oviraptorids may present an additional, more ventral fenestra representing ventral extensions of the antorbital fenestra into the maxillary “body.” In the bottom section, red is the promaxillary fenestra, and blue is the maxillary fenestra. Mickey’s argument is essentially the same as Balanoff & Norell’s.

Leaving aside the issue of who came up with what first (it is quite likely both came up with this independently) this piques my curiosity when it comes to the development and expression of the maxillary and promaxillary fenestrae and their internal diverticulae through the bone, and why they would “switch places,” and what that means for their internal anatomy. There is also the question of support for this hypothesis, as Balanoff & Norell seem to concern themselves merely with external anatomy; tracking the internal structures and associating them with possible homologous features of the bone:

Does the promaxillary diverticulum always lie dorsal, or ventral to the maxillary diverticulum?

Do the tracts for the diverticulae lie alongside one another, but the pockets themselves stay fixed?

Is there a medial association of the antrum in which it can be determined the promaxillary and maxillary fenestrae are always associated, and thus by looking at these — using CT! — a clearer statement be made about the identification of fenestrae?

No matter, this monograph adds more extensive information on the anatomy of oviraptorids in general than we’ve had available, the first extensive description of postcrania for this group available for quite some time.

Balanoff, A. M. & Norell, M. A. 2013. Osteology of Khaan mckennai (Oviraptorosauria: Theropoda). Bulletin of the American Museum of Natural History 372:1-77.
Clark, J. M., Norell, M. A. & Barsbold R. 2001. Two new oviraptorids (Theropoda: Oviraptorosauria), Upper Cretaceous Djadokhta Formation, Ukhaa Tolgod, Mongolia. Journal of Vertebrate Paleontology 21(1):209–213.

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