Re: Caenagnathus species (long?)

["Jaime A. Headden" <qilongia@yahoo.com>]

Tim Williams wrote:

<Basically, there are two sets of criteria for
separating caenagnathid species. The first method
divides the material based largely upon the degree of
coossification of the tarsometarsus. This was the
method employed by Osmolska (1981) and Currie (1989,
1990). Under this scenario, Elmisaurus has a
coossified tarsometatarsus, Chirostenotes does not. 
(Elmisaurus can also be distinguished from
Chirostenotes by additional characters outlined 
above.)...>

  ...as well as having a thinner third manual digit,
more prominent flexor tubercles on the manual claws,
in addition to being shallower, giving the claw a
sharper, for recurved profile, a relatively shorter
pedal digit 1, and flatter ventral side of pedal
claws... *Elmisaurus* is a very well established
genus.

<The second method divides the material on the basis
of the construction of the limb elements - gracile
versus robust. This was the method used by Currie and
Russell (1988) and Sues (1997). The latter author
provided cranial characters for the diagnosis of his
gracile and robust species, courtesy of ROM 43250 and
the Caenagnathus jaw material.>

  I think this method is good, but in its own way, not
as a genus/species identifier/diagnoser, but as Raath
(1990) and Colbert (1990) suggested for their
respective genera (*Syntarsus* and *Coelophysis*), as
sexual dimoprhic indicators. Relative robusticity of
*E. rarus* to *E. elegans,* or *C. pergracilis* to *C.
sternbergi* (= *C. elegans*?) is based on very little
evidence, and as both authors showed, partially
seconded by Carpenter (1990), the femur and pelvis are
the most distinctive probably indicators of sexual
dimorphism. Only *C. pergracilis* preserves the
relavant material, as recognized.

<Sues recognised two North American species: C.
pergracilis and C. elegans. Sues doubted that the
tarsometatarsal characters observed by Osmolska (1981)
and Currie (1989, 1990) were of any diagnostic value,
and regarded Elmisaurus as a suspect genus.>

  The regular form of the metatarsus in *C.
pergracilis* (or at least specimens refered to that
species) is suggestive of regular form in that
species, whereas the abberant form of the metatarsus
in *Elmisaurus* is distinctive enough, including the
tarsal process in the two species, to warrant a
generic identity. Sues' points for differentiating *C.
elegans*' pes from *C. pergracilis*' stands as the
most probable differentiation of the two genera, along
with the characters remarked above. As for *C.
sternbergi*, the mandibular articulation is the only
valid comparative element, as all further jaws of *C.*
cf. *sternbergi* (see Currie, Godfrey, and Nessov,
1994) lack the region for comparison (for all we know,
the spade-tipped jaw could be referrable to *C.
sternbergi* -- anyone at least got a specimen # for
that, or the Sandy material?). Sues (1997) should be
regarded as a suggestion, as the synonymy of "O."
elegans and *C. sternbergi* cannot be verified without
further evidence.

===
Jaime A. Headden

"May I lure us, ere the mote ends us?"

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