Re: Sinornithoides in DA... the first Sleeping Dragon.

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

Torsten van der Lubbe (DragonsClaw@gmx.net) wrote:

<That appears to me to be a clear statement _contra_  Xu & Norell 2004.>

Not to step on Kris' toes replying here, but I think a few clarifications are
needed.

1. Definitive statements required definitive data: The authors clarify their
evidence in the Methods section of the paper, which I quote here:

  "Life posture inference
  "The holotype of *M. long* is inferred to be buried in deposits when the
   animal was sleeping or resting, and thus preserves a life posture.
   Exceptionally well-preserved vertebrate specimens have been collected from
   the Lujiatun beds over the last few years, and it has been proposed that
some
   of them provide information for dinosaur behaviour[3]. The Lujiatun beds are
   alluvial depositsmainly comprising tuffaceous conglomerate debris flows,
   sandstones and mudstones[26]. Some of the most fossiliferous locations are
   considered to be the result of instant catastrophic mass mortality
   events[26,27] preserved in tuffaceous ashes up to 3m in thickness. Although
   not all are volcanic in origin, such Pompeii-like depositional conditions
are
   present in other localities that preserve behavioural characters in fossil
   vertebrates[1,28]. Other dinosaur specimens from the lacustrine beds of the
   Yixian formation[26] and specimens from the more classically fluvial lower
   sandstone beds (such as *Shenzhousaurus*[29]) are not preserved in life
   posture, but in more typical death poses with heads bent back above the
spine
   and the hind appendages and tails extended[30]. Both the specimen itself and
   the sedimentology of the deposits from which this specimen was collected
   indicate that the preserved posture represents a life posture for the
animal.
   Such a posture can also be inferred from the Early Cretaceous troodontid
   *Sinornithoides* from the Ordos basin and perhaps for the nesting
oviraptorid
   *Citipati* (IGM100/979); however, these specimens are incomplete and more
   distorted[1,11]." (pg. 840-841)

  Note: The authors do not cite other evidence of oviraptorids, possibly
*Oviraptor* itself, from Iren Dabasu in the Nei Mongol Autonomous Region, China
(Dong and Currie, 1994). *Citipati* is just much better and more conclusive
evidence, and the specimen they cite isn't even the "good" one (there is a
slightly smaller specimen which pertains to the holotype that is much more
complete overlying a nest in an identical posture).

<Concerning the mode of burial I would think that Xu & Norell proposed
"Pompeii-like depositional conditions" which I would agree with since it
explains both the excellent preservation of the specimen and the apparently
undisturbed 3D-mode of it. Why didnt Mei make an attempt to run away when the
ash started to fall? Possibly because it had been killed in it's sleep by the
vulcanic gasses before.>

  This issue has been debated on the list before. The burial of Pompeii was
rather dramatic and non-instaneous, as Vesuvius was rumbling and sending smoke
into the sky for days before it's eruption. The pyroclastics, which would have
burned the skin and tortured the victims in the second or two before they were
cooked to death was powerful enough to cause the victims to huddle and in many
cases be preserved in defensive positions, showing activity and other fallen as
they ran. The famous mother curled around her child may clearly indicate what
Kris has proposed in *Mei*, as an animal taking a defensive posture to protect
itself, but failed. The gases, which preceded such death assemblies as in the
mid-Miocene Messell deposits in Germany, or the early Oligocene Quercy deposits
in France, may have killed local flora and fauna much as carbon
dioxide/monoxide kills, "silent but deadly".

<So for my sense the easiest explanation for the specimen would be: Mei was
sleeping in it's natural bird-like posture. It got killed by the volcanic
gasses in it's sleep. When the ash began to fall, Mei was already dead and thus
buried gently by a layer of ash thick enough so it could be found well
preserved 128 - 139 million years later.>

  In my opinion, as I think in Kris', this is the "sexiest" and "prettiest"
idea, given that burial in ash beds very seldomly seems to be "peaceful". Take
the Ashfall Beds of Nebraska, USA, which buried hundreds of animals, all on
their sides, do to volcanics (the same kind that buried Pompeii, Herculaneum,
Messell, and Liaoning).

  Cheers,

Jaime A. Headden

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

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