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Re: Deinonychus Morphological Variations within Ontogeny



Nice work.  The study concludes with the hypothesis that juvenile
_Deinonychus_ might have been capable of some form of flapping flight.
This seems entirely reasonable.  However, given that _Deinonychus_ was
a predator, there is potential scope for alternative hypotheses to
flight capability; the ontogenetic changes might be related to a shift
in predatory strategy.  There is evidence that adult _Deinonychus_
targeted large prey (much larger prey if _Tenontosaurus_ was the
target), and the prey was grasped and held using both hands.  Younger
_Deinonychus_ likely targeted smaller prey, perhaps with greater
emphasis on one-handed prehension (as has been inferred previously for
sub-adult _Bambiraptor_).  The greater reach and proportionately
longer and slender manus of juveniles *might* be a flight-related
feature.  Or it might be tied to different prey preference between
juveniles and adults.

There is also the issue of whether _Deinonychus_ (including juveniles)
were capable of flapping at all.  This ability is dependent on the
orientation of the shoulder joint.  Dromaeosaurids have been
reconstructed as having a glenoid that was too ventrally oriented to
permit elevation of the humerus above the back (Senter, 2006).  So
_Deinonychus_ would have been limited to "passive" gliding or other
aerial behaviors that did not entail an upstroke (including WAIR).
Parsons & Parsons claim a more lateral orientation of the glenoid,
citing in support their own 2009 anatomical study of _Deinonychus_.
This orientation would allow some degree of flapping.  So there are
differing interpretations of the scapular glenoid orientation for
dromaeosaurids like _Deinonychus_.  I favor the more ventral
orientation (for dromaeosaurids, as well as for basal avialans such as
archaeopterygids and confuciusornithids), with powered (flapping)
flight not arising until Ornithothoraces.  But I'm happy to be
contradicted on this point.  I like the concept of flying
dromaeosaurs.  However, the biomechanics are currently not very
supportive of this idea.

On Thu, Apr 16, 2015 at 4:54 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
>
>
> New in PLoS ONE:
>
>
> William L. Parsons & Kristen M. Parsons (2015)
> Morphological Variations within the Ontogeny of Deinonychus
> antirrhopus (Theropoda, Dromaeosauridae).
> PLoS ONE 10(4): e0121476.
> doi:10.1371/journal.pone.0121476
> http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121476
>
>
> This research resulted from the determination that MCZ 8791 is a
> specimen of Deinonychus antirrhopus between one and two years of age
> and that the morphological variations within particular growth stages
> of this taxon have yet to be described. The primary goal of the
> research is to identify ontogenetic variations in this taxon.
> Histological analyses determined that the Deinonychus specimens AMNH
> 3015 and MOR 1178 were adults. Comparisons are made between MCZ 8791
> and these adult specimens. The holotype, YPM 5205, and the other
> associated specimens of this taxon within the YPM collection are
> similar in size and morphology to AMNH 3015. Further comparisons were
> made with the three partial specimens OMNH 50268, MCZ 4371, and MOR
> 1182. Although these specimens represent only a partial ontogenetic
> series, a number of morphological variations can be described. One
> secondary goal of this research is to compare the known pattern of
> variable, informative, ontogenetic characters in MCZ 8791 to a similar
> pattern of morphological characters in the sub-adult dromaeosaurid
> specimen Bambiraptor feinbergorum, AMNH FR: 30556. If the characters
> that have been determined to represent variable juvenile morphology in
> the ontogeny of Deinonychus are exhibited in Bambiraptor, this study
> will begin the process of determining whether a similar, conservative,
> ontogenetic pattern exists throughout the rest of Dromaeosauridae. If
> defensible, it may reduce the number of sympatric taxa within this
> clade. The other secondary goal relates to the forelimb function. The
> approximate body size, forelimb length, wrist development, and the
> presence of a more prominent olecranon on the ulna of MCZ 8791 support
> the hypothesis that juveniles of this taxon possessed some form of
> flight capability.