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The material, from Como Bluff, includes distinctive teeth and
perhaps skeletal elements, of an "omnivorous carnivorous [sic]"
dinosaur with a body approximately "coyote-to-wolf size.
Comments by Mickey Mortimer
Material
(TATE 546) (~1.5-4
m) tooth (7.1 mm long, FABL 5.4 mm) (TATE coll.) tooth (~9
mm)
Diagnosis
Currently
indeterminate pending more detailed comparison to several theropod
taxa.
Description
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(?).
Relationships
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).
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