Before I tackle Caudipteryx, I thought I'd enlighten everyone as to the facts behind one of the most mysterious dinosaurs around- "Beelemodon".
"Beelemodon" Bakker 1997
Kimmeridgian-Tothonian, Late Jurassic
Morrison Formation, Wyoming, USA
Material- (TATE 546) (~1.5-4 m) tooth (7.1 mm long, FABL 5.4 mm)
(TATE coll.) tooth (~9 mm)
Currently indeterminate pending more detailed comparison to several theropod taxa.
This taxon is still a nomen nudum, as it is not yet diagnosed, nor does it have a species name. Bakker describes it as an "omnivorouscarnivorous dinosaur of uncertain relations" and an "enigmatic dinosaur". It is supposedly "coyote-to-wolf size". Although using tooth size to determine total length is extremely risky, comparison to various theropods indicates a length of 1.5-4 meters is probable, depending on body form. It is unclear whether postcranial remains can be referred to the taxon, as only teeth are described and illustrated. A single tooth is illustrated in side view and cross section. Another tooth is plotted in the "denticle-width vs. crown height" graph, indicating a slightly larger specimen is known as well.
The illustrated tooth is slightly recurved, laterally compressed (50% as wide as anteroposteriorly long) and missing its distal tip. Fluting is present on the illustrated side. The root is constricted, the anterior carina lacks serrations and the posterior carina has serrations extending to the base. The serrations are small (4.3 per mm, ~35 on the whole crown), pointed and project slightly distally. The cross section indicates it was fairly symmetrical labiolingually, narrowing anteriorly and exhibiting a slight anterior expansion labially(?) and a slight posterior expansion lingually(?).
At first glance, these specimens look very similar to ornithischian premaxillary teeth. The posterior two premaxillary teeth of Lesothosaurus have anterior serrations, but lack them posteriorly except at the tip. This is the reverse of the case in "Beelemodon". The serrations are comparatively larger (~15 per tooth if they extended as proximally as in "Beelemodon") and do not extend to the base of the crown. Drinker has a very similar tooth morphology, with serrations present only on the posterior carina. These serrations are slightly larger (25-30 per tooth) and have longer interdenticle slits. The tooth itself is not recurved, but is otherwise similar in shape. Galtonia also has similarily shaped teeth, but with larger serrations and anterior serrations present distally. "Beelemodon" is obviously based on theropod maxillary or dentary teeth however, as the premaxillary teeth of most theropods have serrations displaced so that the distance between them is much longer labially than lingually. Troodontids, tyrannosaurids and ornithischians have premaxillary teeth that not only have the latter character, but are also much wider labiolingually than "Beelemodon". The cross section of "Beelemodon" is very similar to theropod maxillary and dentary teeth.
While "Beelemodon" is obviously theropod, placing it within that clade is a more difficult task. The constricted root is known in Compsognathus, Pelecanimimus, segnosaurs, Protarchaeopteryx, Caudipteryx, mononykines, Archaeornithoides, troodontids, Microraptor, Archaeopteryx and toothed pygostylians. Therefore, chances are pretty good this is a coelurosaur. Compsognathus has some teeth that have unserrated anterior carinae and serrated posterior carinae. These have larger serrations relative to crown height (20-25 per tooth). They are shaped similarily and have similar serration morphology. Pelecanimimus has yet to be described in detail, but has both anterior and posterior carinae unserrated. Segnosaurs differ in having crowns that are less recurved, more elongate and labiolingually wider, with much larger posterior serrations (8-10 per tooth) and equally sized anterior serrations. Protarchaeopteryx is described briefly, but differs in having anterior serrations that are slightly larger compared to crown height (20-30 per tooth). The highly elongate, needle-like teeth of Caudipteryx lack serrations altogether, so are very dissimilar. Mononykus has unserrated carinae, more elongate and less recurved crowns. The teeth of Archaeornithoides differ in lacking both serrations and carinae, as well as being nearly conical. Archaeopteryx has teeth that are completely unserrated, lack posterior carinae and are much wider labiolingually. They are similarily proportioned and have unserrated anterior carinae. Some troodontid teeth lack anterior serrations, but have them posteriorly, and are laterally compressed. The teeth of "Beelemodon" differ from troodontids in being less recurved, lacking hooked serrations and having comparatively smaller serrations (compared to 15-20 per tooth). Microraptor is similar in having crowns with unserrated anterior carinae and posterior carinae with distally projecting serrations. It differs in having larger serrations in comparison to crown height (20-25 per tooth), longer blood grooves and a wider crown. Pygostylians have unserrated crowns without carinae that are very wide, so are similar to Archaeornithoides, but dissimilar to "Beelemodon". "Velociraptorines" also sometimes lack anterior serrations, are laterally compressed and have similar amounts of serrations (15-35), but are more recurved and lack basal constriction.
Therefore, the greatest resemblence is to Compsognathus, although the few facts known about Protarchaeopteryx are also in agreement and a deinonychosaur might also be expected to evolve a similar tooth, judging by comparisons with Microraptor, Saurornitholestes and Morrison "velociraptorine" teeth (Britt 1991). Are there any theropods already known from the Morrison Formation that could have "Beelemodon" teeth? Although Morrison compsognathids are not known, both Coelurus and Ornitholestes are close phylogenetically and have poorly described or unknown teeth. Protarchaeopteryx comes out as a segnosaur-oviraptorosaur in my phylogeny, so perhaps these teeth belong to the Morrison segnosaur-oviraptorosaur, known from two cervical vertebrae. Finally, although reported Morrison "velociraptorine" teeth lack constricted roots (Britt 1991), it is not inconceivable "Paleopteryx" had a mix of avian and dromaeosaur characters in it's teeth, like Microraptor. There are therefore several taxa to which "Beelemodon" could be reasonably referred. However, as it is currently impossible to chose one over another, they should be left separate. Given the amount of variation in serration number in a single theropod genus (Allosaurus- 20-35; Saurornitholestes- 15-35), there is no way to separate "Beelemodon" from Compsognathus or Protarchaeopteryx at this point. Because of this, it must remain indeterminate. The fluting or serration morphology may eventually prove diagnostic, but this cannot be determined from the available literature. I recommend classifying "Beelemodon" as a provisionally indeterminate coelurosaurian nomen nudum until further research is done.
reference- Raptor family values: Allosaur parents brought great carcasses into their lair to feed their young. Bakker, R. In “Dinofest International”, Proceedings of a Symposium, Academy of Natural Sciences, eds Wolberg, Sump and Rosenberg, 51 - 63 (1997).
Anyone who wants a scan of the tooth, ask me offlist.