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Re: [dinosaur] Zhongjianosaurus, new tiny microraptorine dromaeosaurid from Early Cretaceous of China (free pdf)



The idea of niche partitioning among Jehol dromaeosaurids sounds
entirely reasonable.  After all, there is a huge disparity in size,
and substantial variation in limb proportions.  But I really doubt
that this niche partitioning followed a terrestrial/arboreal divide,
with the smallest of the Jehol dromaeosaurids being arboreal and the
larger ones being fully terrestrial.  I think this is what Xu and Qin
mean by "small-sized Jehol dromaeosaurids such as _Microraptor_ are
more likely to have been arboreal or even gliding animals".  The
implication is that tiny _Zhongjianosaurus_ (like _MIcroraptor) was
arboreal, and therefore possibly also a glider.

First of all, I'm highly skeptical that _Microraptor_ was "arboreal".
Okay, so it might have climbed trees occasionally; but the skeleton of
_Microraptor_ is not adapted for either bipedal or quadrupedal
climbing, let alone perching.  Like all dromaeosaurids, the skeleton
has the proportions of a cursorial biped.  (Ditto for
_Archaeopteryx_.)

Second of all, despite _Zhongjianosaurus_ being extremely small - "the
smallest known (osteologically adult) Jehol dromaeosaurid" - this
microraptorine looks even less adapted for arboreality than
_Microraptor_.  Curiously, the authors mention pedal proportions in
support of arboreality in _Zhongjianosaurus_: longer pedal III-3
relative to III-2.  But III-3 is not that much longer than III-2 (5.6
vs 5.5 mm), and feet specialized for grasping tend to have a highly
elongated III-3.  Besides, without knowing the length of III-1, any
functional interpretation of the third toe is limited (arguably even
pointless).  Even more curiously, the authors cite Dececchi and
Larsson (2011), even though Dececchi and Larsson state that
microraptorines were non-arboreal, with pedal phalangeal indices
identical to those of terrestrial non-avian theropods.

On a positive note, it's nice that this little theropod was named
after the eminent Chinese paleontologist Prof. Yang Zhongjian (known
historically in the Western world as Chung-Chien Young or "C.C.
Young").  The Cretaceous bird _Zhongjianornis yangi_ (named 2009) also
takes his full name.  Previously, dinosaurs named in his honor used
the romanized version, e.g. _Yimenosaurus youngi_, _Fulengia youngi_
(originally described as a lizard).



On Tue, Apr 11, 2017 at 2:22 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>
> Ben Creisler
> bcreisler@gmail.com
>
>
> A new paper in open access:
>
>
> XU Xing and QIN Zi-Chuan (2017)
> A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of
> western Liaoning and niche differentiation among the Jehol dromaeosaurids.
> Vertebrate PalAsiatica (advance online publication)
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ivpp.ac.cn_cbw_gjzdwxb_pressonline_201704_t20170410-5F4772854.html&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=95ugNj5LtH6wHh2GuTs867J4et1jZVrhvcb6BUAVajs&s=QaRMMZSsVnsJ5o6p7P4M9Jh6QBcmeTL4xY480sWj-2M&e=
>  
>
> Free pdf:
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ivpp.ac.cn_cbw_gjzdwxb_pressonline_201704_P020170410587218147108.pdf&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=95ugNj5LtH6wHh2GuTs867J4et1jZVrhvcb6BUAVajs&s=2QO7EHiV4zCSFS_RpY1CeWud0PJ0z-D4UL70Lq0-GX4&e=
>  
>
>
> The Early Cretaceous Jehol dromaeosaurids are taxonomically and
> morphologically diverse, and one of them, Microraptor zhaoianus, has been
> suggested to be among the smallest known non-avialan theropods. However,
> this idea is based on specimens of relatively early ontogenetic stages, and
> the lower limit of the mature body mass of Jehol dromaeosaurids thus remains
> unknown. Here we describe a new dromaeosaurid, Zhongjianosaurus yangi gen.
> et sp. nov., based on a specimen from the Lower Cretaceous Yixian Formation
> (the middle section of the Jehol Group) from Sihedang, Lingyuan County,
> Liaoning in Northeast China. While this new taxon is referable to the
> Microraptorinae, it differs from other microraptorine dromaeosaurids in
> numerous features, most notably the fusion of proportionally long uncinate
> processes to dorsal ribs, a humerus with a strongly medially offset proximal
> end and a large fenestra within the deltopectoral crest, an ulna slightly
> longer than the humerus, and an arctometatarsalian pes. Most significantly,
> the estimated 0.31 kg mass of the Z. yangi holotype of an adult individual
> confirms that some Jehol dromaeosaurids are among the smallest known
> non-avialan theropods. Our preliminary analysis demonstrates niche
> differentiation among the Jehol dromaeosaurids, a phenomenon rarely reported
> among Mesozoic dinosaurian faunas.
>