[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Anzu wyliei, near-complete caenagnathid oviraptorosaurian

There is much to agree with what Tim said, but it's too early to
suggest this. GM and statistical analyses of caenagnathid feetw ould
be useful when assessing capability of the foot in tranducing forces
while walking, running, etc. One notable thing is that length of pd-IV
seems a greater predictor of cursorial ability in theropods and birds
than length of pd-II. This is especially true when you consider that
in some taxa, pd-II is lost, but never pd-IV. The ungual in pd-IV is
also quite small in *Macrophalangia canadensis* (CMN 8538), despite
large size of md-I and its ungual. pd-II and IV are subequal,
revealing likely absence of high predatory capability. If generalists
then, regardless of distal position of pd-I and its large ungual, the
foot suggests limited grasping ability. Biomech analyses would be

And yes, caenagnathids seem to develop towards an arctometatarsus,
despite the rest of the foot, which implies the pes was dealing with
torsional forces and the third metatarsal differently. How? Unclear,
but it does suggest at least high mobility rather than necessarily
speed. That means not really cursoriality. The elongated first toe
falls in line with this, in acting as a stabilizer and secondary
gripping device (Fowler et al. 2011). An "Ornithomimus" elegans
specimen from Hell Creek (MOR 759, Varricchio, 2001) shows broader
phalanges, including unguals, than in *Macrophalangia canadensis*, a
feature that has been pointed out. Caenagnathid toes are generally
slender, but in *Elmisaurus* they are not where the articular surfaces
are broader but proportionately the phalanges and metatsarsi retain
proportionate diameters. Yet regardless this, the toes appear about
the same size, with *Elmisaurus* having smaller first toes. These
suggest at least somewhat ecological distinction, either trophic or
environmental adaptation. But to claim the one rather than the other
requires substantially more data.

Fowler, D. W., Freedman, E. A., Scannella, J. B. & Kambic, R. E. 2011.
The predatory ecology of Deinonychus and the origin of flapping in
birds. PLoS ONE 6 (12): e28964. doi:10.1371/journal.pone.0028964
Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda)
dinosaurs from Montana. pp. 42-57 in Tanke, Carpenter & Skrepnick
(eds.) Mesozoic Vertebrate Life: New Research Inspired by the
Paleontology of Philip J. Currie. Indiana University Press
(Bloomington & Indianapolis).

On Sun, Mar 23, 2014 at 6:17 PM, Tim Williams <tijawi@gmail.com> wrote:
> Jay <jayp.nair@yahoo.com> wrote:
>> Congrats to Matt Lamanna and the other authors on this awesomeness; this 
>> paper presents the first decent look into the complete morphology of 
>> caenagnathids:
> I'll second that.  It even has an eminently cool name.  It's amazing
> that our knowledge of the anatomy of derived caenagnathids has
> advanced so far, in a large part thanks to _Anzu_.  We've come a long
> way since the first _Caenagnathus_ jawbone was regarded as coming from
> a bird (Sternberg, 1940); and all we had to go on for the postcranial
> skeleton of caenagnathids was tantalizing hand- and foot-bones (the
> latter often called "elmisaurids").
> A couple of studies (including this one by Lamanna et al., as well as
> Longrich et al. [2013]) have mentioned the odd pedal morphology of
> caenagnathids - especially their long toes and relatively elongated
> penultimate phalanges.  One suggestion is that the proportions of the
> non-ungual phalanges, especially the relatively long penultimate
> (ungual-bearing) phalanges, made the pes more adapted for grasping
> than running.  So it follows that the pes might have been used for
> prey capture or even climbing.
> However... this idea shouldn't be taken too far.  Hopson (2001) found
> that, among birds, the phalangeal proportions of the third toe were a
> fairly reliable indicator of habits.  Using the pes of the
> caenagnathid _Chirostenotes_ as an example (based on the specimen
> originally named _Macrophalangia_), it is true the penultimate phalanx
> of the third toe is quite long by non-avian theropod standards (about
> 31.5% the length of the total non-ungual digit length).  Also, the
> first phalanx is relatively short (~40.5%) - quite unlike what is seen
> in highly cursorial birds.  But the phalangeal proportions are a long
> way from the feet of specialized grasping birds, where the penultimate
> phalanx is typically over 40% of the non-ungual digit length (in the
> osprey and swifts it's over 50%).
> The phalangeal proportions of _Chirostenotes_'s third toe are not too
> different from those of _Coelophysis_.  So rather than representing a
> shift to a 'better' grasping foot, caenagnathids might represent a
> reversal toward a more generalized, less cursorial type of foot. The
> long toes and phalangeal proportions of _Chirostenotes_ are similar to
> those of the moorhen ("swamp chicken"), which might suggest a
> preference for wetlands.  Lamanna et al. mention that the depositional
> environments of caenagnathid fossils suggest that these theropods were
> "adapted to wetter, more humid surroundings".  This fits with an old
> hypothesis that the long hindlimbs (especially the metatarsus) and
> large feet of caenagnathids were adaptations for wading (Currie and
> Russell, 1988).  However, I wouldn't read too much into the pedal
> proportions (and long hindlimbs) in inferring wading habits for
> caenagnathids, including _Chirostenotes_ and _Anzu_.  It may just be,
> as Lamanna et al. suggest, that caenagnathids were ecological
> generalists.  So they may occasionally have ventured into shallow
> water to feed, without being specialized waders.  Either way, the
> evidence points to a very different ecology to oviraptorids, as
> Lamanna &c make clear.
> Caenagnathids also had an arctometatarsalian foot, which may seem
> strange for non-cursorial animals.  Nevertheless, although this
> feature is found in highly cursorial theropods, it may not be a
> cursorial adaptation per se, and be more concerned with energy
> transduction.  (A near-arctometatarsalian condition is seen in
> _MIcroraptor_, which was also distinctly un-cursorial.)
> Cheers
> Tim

Jaime A. Headden
The Bite Stuff: http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)