Better Know an [Oviraptorid] — The First Egg Thief

Scientists are often busy fellows, so that when they find and describe a new animal, they must often do so in steps, preparing longer works of description as they do their other things. Some taxa wait a few years, others a few decades. Oviraptor philoceratops has waited for almost 100 years.After its initial description in a small paper, described along with Velociraptor mongoliensis and Saurornithoides mongoliensis (in Osborn, 1924), Henry Fairfield Osborn left the specimen to be mounted in a panel in the American Museum of Natural History, New York City, and promptly when on to a few other things. Treatment was not returned to this specimen until the early 1990’s, when the panel was taken down as part of a re-preparation effort on the part of AMNH staff after the finding of troves of oviraptorid fossils in southern Mongolia. David Smith ended up describing some of this new preparation, but many things were and remain obscured, and smith got a few things wrong. For one, he continued the trend in rendering Oviraptor philoceratops as a low-skulled, short-necked oddity that Greg Paul had developed in 1988, and the reconstructions differed very little from that of the previous several decades, including Osborn’s own. I covered some of this here. So much of the background on Oviraptor philoceratops was covered on the “Myth of the Oviraptor” story that it serves as a jumping point for this post, which is then a decent #2.

Preserved material of AMNH FR6517, holotype of Oviraptor philoceratops Osbron (1924).

Oviraptor philoceratops is not completely preserved. For one thing, it’s missing half of the skeleton. Additional difficulties include the way that portions of the skeleton, especially the skull, have been rendered in media. Above is an illustration as it appears in Norell, Gaffney and Dingus’ 1994 volume, Discovering Dinosaurs (pg. 125), depicting the form of the original wall mount. Obscured is the beautiful contrast in color, whitish yellowed bone on ruddy sandstone. The hands are clutched around the remains of eggshells, likely associated, while in the rear of the preserved portion, a small lizard skeleton is preserved, although it has never been described. The bones are in relatively poor condition, riddled-through with the bore holes of insects.

AMNH FR6517 is also the first nonavian dinosaur to show evidence of  a distinct furcula, although Osborn called it an interclavicle (only birds had furculae, or wishbones, you see). Previous examples of clavicular structures were found with coelophysoids, like Segisaurus halli Camp (1936), and later shown to be furcula, but these discoveries  followed that of Oviraptor philoceratops (Carrano et al., 2005).

Skull of AMNH FR6517, holotype of Oviraptor philoceratops Osborn (1924). Light grey areas are preserved bone, but lack preserved surface, while dark grey areas indicates missing material.

Osborn toyed around with the name a little bit. In a presentation before the American Museum, he granted the name “Fenestrosaurus,” but as this was never published in a legitimate venue, the name has been taken as a nomen nudum, and I would argue even that and put the name in quotes. But the reasoning and purpose of the name is clear: Osborn wanted to indicate the unusual form of the skull, otherwise unknown at the time among virtually any terrestrial vertebrae, a skull comprising of many splints and bars, and lots of large fenestrae (antorbital, maxillary, orbit and infratemporal, while the mandible had a huge, whopping avian-style mandibular fenestra (otherwise seen primarily among the phorusrhacoids). Reconstructions of this skull vary heavily, largely due to the incompleteness, and many illustrators have chosen to take Osborn’s as gospel. Above, I have illustrated what is preserved of the skull and placed a hypothetical “minimum” projection of the skull’s true extent, but this obscures a few details, which are made apparent when certain features are taken into account.

The skull is crushed, so reconstructing is purely as seen is problematic. One side of the skull is skewed posteriorly, so that the occiput and middle regions of the skull are distorted, bent, and stretched out of position. The occiput is much narrower than it is likely to be. The parietals are preserved rather than as a long tubular structure as they are in other oviraptorids, but as a tall, steepled pair of plates. They are not fused. This is particularly interesting because virtually all other oviraptorids have fused parietals, a sign of maturity. The tall, thin parietals form a blade, and in Rinchenia mongoliensis, these are the posterior-most extent of the cranial crest. Does Oviraptor then have a crest extending to the parietal? I think this is very likely. The frontals that are preserved are incomplete along their midline, and do not match up with one another, and despite their incomplete preservation, it is possible to suggest that they are oriented in a more dorsal fashion as shown, rather than flatter as in other oviraptorids; however, this is pure speculation, and the frontals of Rinchenia mongoliensis are dorsolaterally concave, while those of Oviraptor philoceratops are convex (as in other oviraptorids). This then implies that if there was a cranial crest, it may have been rather short. In the skeletal reconstruction below, I have illustrated what is likely to be the maximum extent of such a crest.

So after noting that Oviraptor philoceratops might have had a cranial crest, we wonder then about the next odd thing, the shape of the maxilla. Only two oviraptorosaurs have maxillae like this, a long element with a ventrally convex margin and large antorbital fossae: ROM 43250 and the Triebold specimens, CM 78000 and 78001. The latter two are undescribed, but casts of their skull are widely known, and this observation is drawn from that. This tells us that Oviraptor philoceratops had a particularly long face compared to all other oviraptorids, and that it was one of the most basal oviraptorids. However, this analysis is not based on much; most analyses using AMNH FR6517 have found it to shift around, likely due to improper coding, or lack of resolution with fewer features that could indicate otherwise.

Skeletal reconstruction of AMNH FR6517, holotype of Oviraptor philoceratops Osborn (1924). Shown is all preserved material. Not accurately scaled.

Oviraptor philoceratops is a small animal, comparatively speaking. Most oviraptorids are fairly tiny, between 1.5 and 4 feet in length. Oviraptor philoceratops was not that much larger. The skull length compares favorably around 1/10th of the total body length in several oviraptorids, while in Citipati osmolskae and MPC-D 100/42 (the Zamyn Khondt “oviraptorine”), the ratio is a bit lower as the neck is longer in comparison. The skull of Oviraptor philoceratops would have been about 11cm, or a bit over 4in, long, but was probably immature (the above skeleton is not correctly scaled). This projects a length of around 1.1m, or 3.5 ft, and it would have been a little larger the holotype of Khaan mckennai, and larger if more mature (maybe not by much).

There are several unique features of the taxon, affirming its uniqueness, although as the nominative taxon for the Oviraptorosauria, this should come as no surprise (although it happens on occasion that the nominative type is a piece of crap, such as that of Allosaurus fragilis, and many others).

1. The maxilla is elongate with a ventral convex tomial margin, and with a maxillary fenestra that takes up much of the antorbital fossa (as in most oviraptorids), distinguishing it from ROM 43250.
2. The profile of the mandible, and of the external mandibular fenestra, is very low and long, intermediate in form between caenagnathids and virtually all other oviraptorids.

These features separate Oviraptor philoceratops, and also appear to place it at the base of Oviraptoridae, although this is not supported by current phylogenetic analyses. If this is true, the term Oviraptorinae in an explicit phylogenetic sense would be equivalent to Oviraptoridae, while the clade of crested oviraptorids (if it exists) would have to use a different monicker. This clade generally comprises Citipati osmolskae, Rinchenia mongoliensis, MPC-D 100/42, Nemegtomaia barsboldi, and whatever the hell this is:

Cast of the skull and manus of an undescribed oviraptorid, cast by Gaston Design from the original which is held in private hands. Image from the Witmer Lab.

I’m including this image because it’s important to note several things. Primary among them is the importance of specimens like this to arrive in the hands of researchers, especially if they are placed in the care and study of institutions and in the public domain. Not only does this increase the knowledge that can be derived from such specimens (as a cast, this specimen tells us only about shapes of the surface of the skull and manus, while as a private specimen, privately collected, precise provenance and association details are unavailable), it allows further workers to examine, verify, validate, or reject previous arguments made using it. But that is all fine and dandy as an ethical “standard,” but this specimen is also reflective of a type that could very well be unique, and if it is, its availability to science increases our knowledge through the support of science workers who use the papers and publicity generated from noting these things to improving science and education (when possible). If this skull represents a new taxon, which it might very well do, it would be amazingly useful to nerds like me who want to study the [CENSORED] out of it. I can only do so much from a photograph, or cast. [n1]

Whatever the significance of undescribed specimens like the “mitre-crested” form above (simply an exaggeration of the Nemegtomaia barsboldi crest, but there are differences), there is a dearth of attention focused on AMNH FR6517; while Smith described the specimen in more detail than Osborn, it was not subjected to the level of detailed description and illustration that lends researchers the ability to validate the work, and several new taxa have been published on in brief, then later in full in one fashion or another, including Heyuannia hwangi (described by Lü in 2002, followed by Lü, 2005 (a book) and Lü et al., 2005), Citipati osmolskae (described by Clark, Norell and Barsbold in 2001, followed by detailed description of the skull by Clark et al., 2002; the postcranium was described in detail by Clark et al., 1999, but it belongs to a specimen other than the Citipati osmolskae holotype). The nominating taxon deserves a fuller, and more detailed, illustrated, and phylogenetically sound analysis, as several things I’ve noted here beg for its clarification.

[n1] I am nontheless informed that a second specimen is in the hands of researchers, and it is informative of the first, although not nearly as complete (no manus attached). However, something is better than nothing in this case, and that’s a Good Thing.

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