Ambiguity in an Australian Dinosaur

Based on a single bone from the Lightning Ridge locality of Griman Creek, Victoria, Austrialia, Rapator is a large dinosaur from the middle Cretaceous (Aptian--Albian) that has puzzled researchers for decades. Since it was described by von Huene in 1932, researchers have patently used his identification of the only element as the first metacarpal of a coelurosaurian animal, or often something more carnosaurian or ceratosaurian. The last was a conclusion arrived at by Long in 1999, but so far, nothing definitive has been reached as to it's identity. Von Huene drew comparison to Ornitholestes, and this became obvious in his selection of a specific epithet, which translates to "like or in the shape of Ornitholestes." The generic, "first" name, however, has no provided etymology, and this has become problematic to students of the name. There is no Latin source for the name, except the word raptor; in Latin, any declension of the word does not possess the rapa- (note the highlighted section) structure, and in this appears to be a misinterpretation or poor attempt at forming a nominative noun -- from a noun. Thus, the name may simply mean "raptor; one who snatches, siezes; the snatcher, the seizer." However, Ben Creisler (here; go to section II, Translations, and select dinosaurs, then "R", and find Rapator) offers an alternative solution, raptor + -ator, Latin for "seizer" and "one who does." This however, is apparently redundant, as raptor already carries this active connotation (see above). Another solution (Tim Williams, pers. comm.) is a bizarre variation of rapax (rapacious, plunderous, inordinately greedy) or a combination of rapax and -ator or rapax and raptor, forming "one who plunders, plunderer." We have no source for von Huene's intent and can only hope we can come close.

Fig. 1. Preserved material of Rapator ornitholestoides, BMNH R3718, either the first metacarpal or the first phalanx of the first digit. On the top row, left to right: dorsal, ventral, medial, and lateral; on the bottom row: distal and proximal views. The bone measures 7cm along it's length, though von Huene's measurment is not based on a particular axis that can be verified from figures. It is proximally 4.5cm wide, 4cm wide distally, and in the middle it is 2.5cm.

    Recently, new research has led to an innovative idea, one which even von Huene himself dismissed on the basis of the then-current fossil record; that the bone he called a first metacarpal was in fact the first, proximal phalanx of the first digit. Von Huene tried to show how this was not possible because the proximal articular facet for the first manual phalanx of any digit typically has two facets, or cotyli, to match the two distal condyles of the metacarpals. That he compared this taxon to Ornithomimus is intriguing because in that taxon, the third metacarpal has a single condylar ball and the proximal phalanx of the third digit has but one cotylus. Placing the bone within the digit then opens up new possibilities for comparison. Current research on this topic is in press, though through the preemptive actions of Tim Williams, PhD (here), and myself (here; no PhD, though) in a public forum (The Dinosaur Mailinglist), some of it has come to light completely independantly: Rapator may be an Australian alvarezsaurian, related to the Mongolian Mononykus and Shuvuuia, and the Argentinian Patagonykus. In this it agrees in both the proximal single cotylus of the first pollecial (thumb) phalanx, the enlarged crests on the medial, ventral edge, the asymmetry of the distal condyles (for the first claw) and their vague hourglass-shape when viewed from end-on, and in general appearance. If so, Rapator will be the largest alvarezsaur. However, a detailed comparison is not yet in evidence though is underway (and in press, so just wait for the paper).

Fig. 2. First phalanx of the first digit of Mononykus olecranus, GI (SPS) 107/6 (holotype). Left to right, dorsal and medial views, and below, in proximal view.

    Curiously, among the other remains von Huene described from Australia was an ambiguous vertebra from the caudal series that he named Walgettosuchus woodwardi. A camellate internal structure, neural arch very narrow and with the postzygapophyseal facets on a single process, neural spine nearly absent, and the likelihood of each prezygapophyseal facet on a single, unified process, suggest that the element belongs to a theropod. The provenance of the vertebra is the same as that of Rapator, and this is in itself interesting (Tim Williams, pers comm.) The vertebra compares well with the caudals of Shuvuuia (personal observation) and thus both Australian taxa may actually be congeneric (are the same taxon), and in comparison.

Fig. 3. The caudal vertebra of Walgettosuchus woodwardi, BMNH R3717, in dorsal, left lateral, and distal views; in dorsal and left-lateral views, the proximal end is to the left.

    Meanwhile, I have translated von Huene's original text (a whole three paragraphs but well more than all else that has been written on Rapator put together), and this is available here.

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References (and a more extensive draft, with more illustrations) are forthcoming, but one is available in the document above. Caution: the document is in Word 2000 format, but I will be able to modify the document at request if emailed at qilongia@yahoo.com. Please bear in mind: the contents of this website are mine; do not copy or reproduce or download anything without my permission.