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

Re: Australian Lark Quarry dinosaur stampede trigger scenario unlikely



Rescued from truncation:

From: Stephen Poropat <stephenfporopat@gmail.com>


As with the earlier papers written on this subject by these authors
(Romilio and Salisbury, 2011; Romilio et al., 2013), it seems to me that
there is a fundamental flaw with the hypothesis upheld by Romilio and
Salisbury (2014) that any or many of the tracks at the Dinosaur Stampede at
Lark Quarry Conservation Park were formed underwater:

How did the water level change without disturbing the site?

The reaction rim to the left of one of the large track maker's footprints
(Figure 13 in Romilio and Salisbury, 2014) has 6 cm of relief above the
track layer, yet shows no sign of distortion of any kind. This is despite
it being the only point of significant positive relief on the entire track
site. I visited Lark Quarry on Sunday, and observed that this was so for
myself.

The large track maker's footprints (cf. *Tyrannosauropus* in the original
parlance [Thulborn and Wade, 1984], *Amblydactylus* cf. *A. gethingi* in
Romilio's previous works [Romilio and Salisbury, 2011; Romilio et al.,
2013] and now cf. *Iguanodontipus* in the latest paper [Romilio and
Salisbury, 2014]) have to have been made before at least some of the small
footprints (originally *Skartopus australis* and *Wintonopus latomorum*
[Thulborn and Wade, 1984], all considered to belong to the latter by
Romilio and colleagues [Romilio and Salisbury, 2014; Romilio et al., 2013])
because several of said small tracks overprint the large trackway (e.g.
Thulborn and Wade, 1979: fig. 2B). This was stated explicitly by Thulborn
and Wade (1984: p. 418): =E2=80=9CFootprints in the latter three groups [i.=
e. those
they identified as cf. *Tyrannosauropus*, *Skartopus* and *Wintonopus*])
are equally well preserved, and all of them seem to have been formed at
about the same time. These footprints were formed after the muddy substrate
had been exposed long enough to have attained a firm plastic consistency.
>From the evidence of superimposed footprints it is clear that the carnosaur
traversed the Lark Quarry area before some, at least, of the ornithopods
and coelurosaurs did so.=E2=80=9D

Bearing that in mind: if the small track makers were even partially buoyed
when they traversed the area, how did the large dinosaur's tracks (and
their reaction rims) avoid destruction by the flow of the water? Why were
they not virtually obliterated like the large tracks formed elsewhere in
the site (Thulborn and Wade, 1984)? The relevant passage in Thulborn and
Wade (1984: p. 417), regarding what must have been the first tracks formed
at the site: =E2=80=9CRemnants of a few trackways made by fairly large bipe=
dal
dinosaurs. These remnants comprise scattered footprints which are very
poorly preserved and have no preferred orientation=E2=80=A6 They seem to ha=
ve been
formed, then eroded and filled with water-laid sediment, well before the
substrate was exposed to the air and the other footprints were formed at
Lark Quarry.=E2=80=9D An additional passage on the same page (Thulborn and =
Wade,
1984: p. 417), in reference to a single medium-sized ornithopod trackway
which must have been formed after the first tracks were formed, but before
the stampede: =E2=80=9Csome of its footprints were deeply impressed in soft
waterlogged mud and others (in lower-lying areas) were partly destroyed by
scouring. This trackway seems to have been formed at about the time the
substrate was draining free of surface water and was becoming exposed to
the air.=E2=80=9D

How did the substrate retain the capacity to preserve several successions
of subaqueous tracks (as proposed by Romilio et al., 2013) after drying out
sufficiently (but not totally: =E2=80=9CThe mud was exposed long enough to =
achieve
a firm plastic consistency, but not long enough for desiccation cracks to
appear=E2=80=9D [Thulborn and Wade, 1984: p. 419]) to preserve the large tr=
ackway
in the first place? Romilio et al. (2013: p. 116) state that =E2=80=9CThe
variability in the size of the swim traces, and, by inference, that of
their makers means that not all the animals could have been swimming and
touching the substrate at the same water depth. In the context of this
interpretation, Lark Quarry most likely represents an accumulation of
tracks over a period of time (perhaps days), during which water level
fluctuated, with the majority of the smaller animals swimming or wading,
and the larger animals walking or wading, and many animals using the
current to assist their movements.=E2=80=9D If we accept this, then for the
original sets (representing an absolute minimum of three medium-sized=E2=80=
=93large
bipedal dinosaurs =E2=80=93 sets A, B, and C in Thulborn and Wade [1984: p.=
 417])
of large tracks to have been preserved, they must have dried sufficiently
(but, as we have seen, not completely) to not be affected by water flow
after formation. How, then, could smaller tracks have been made by lighter
dinosaurs in this mud?

In my opinion, and I may be wrong (and would like to have it demonstrated
to me if so), you cannot have it either way.

The mud would have to been exposed, albeit moist, for both the large track
maker's footprints and the small track makers=E2=80=99 footprints to be pre=
served,
as originally proposed by Thulborn and Wade (1979, 1984). If the large
footprints were formed when the mud was exposed, but then water covered the
site to a depth sufficient to buoy several different size groups of small
dinosaurs, then either the large track maker=E2=80=99s footprints would hav=
e been
obliterated (which they weren=E2=80=99t), or the mud would have had to have=
 dried
sufficiently to retain the structure of the large track maker's footprints,
which would then preclude it from preserving any sets of footprints from
smaller dinosaurs (which it did), unless said mud became soft again which
surely would have obliterated the large track maker=E2=80=99s prints (which=
 it
didn=E2=80=99t).

The interpretation presented by Thulborn and Wade (1984) is, in my mind,
still more parsimonious:
1) site shallowly submerged;
2) large ornithopods come through;
3) single ornithopod comes through as site drains;
4) theropod (Thulborn [2013] thoroughly dismantled the methodology which
Romilio and Salisbury [2011] employed in an attempt to show otherwise)
comes through, turns and accelerates at end of preserved trackway;
5) cue stampede;
6) sediment dries (but not to the point of desiccation crack formation); an=
d
7) site floods.

I would have to revisit the site for myself to determine when the probable
vegetation drag marks were made and where they fit into this sequence.

In my opinion (whatever that is worth), Thulborn and Wade=E2=80=99s origina=
l
hypothesis is not perfect, but is far closer to the truth than that
presented by Romilio and colleagues.

References

Romilio, A., Salisbury, S.W., 2011. A reassessment of large theropod
dinosaur tracks from the mid-Cretaceous (late Albian-Cenomanian) Winton
Formation of Lark Quarry, central-western Queensland, Australia: a case for
mistaken identity. Cretaceous Research 32, 135=E2=80=93142.
Romilio, A., Salisbury, S.W., 2014. Large dinosaurian tracks from the Upper
Cretaceous (Cenomanian=E2=80=93Turonian) portion of the Winton Formation, L=
ark
Quarry, central-western Queensland, Australia: 3D photogrammetric analysis
renders the =E2=80=98stampede trigger=E2=80=99 scenario unlikely. Cretaceou=
s Research 51,
186=E2=80=93207.
Romilio, A., Tucker, R.T., Salisbury, S.W., 2013. Reevaluation of the Lark
Quarry dinosaur Tracksite (late Albian=E2=80=93Cenomanian Winton Formation,
central-western Queensland, Australia): no longer a stampede? Journal of
Vertebrate Paleontology 33, 102=E2=80=93120.
Thulborn, R.A., 2013. Lark Quarry revisited: a critique of methods used to
identify a large dinosaurian track-maker in the Winton Formation
(Albian=E2=80=93Cenomanian), western Queensland, Australia. Alcheringa 37, =
312=E2=80=93330.
Thulborn, R.A., Wade, M., 1979. Dinosaur stampede in the Cretaceous of
Queensland. Lethaia 12, 275=E2=80=93279.
Thulborn, R.A., Wade, M., 1984. Dinosaur trackways in the Winton Formation
(mid-Cretaceous) of Queensland. Memoirs of the Queensland Museum 21,
413=E2=80=93517.


On 9 July 2014 00:17, Ben Creisler <bcreisler@gmail.com> wrote:

> Ben Creisler
> bcreisler@gmail.com
>
> A new paper:
>
> Anthony Romilio & Steven W. Salisbury (2014)
> Large dinosaurian tracks from the Upper Cretaceous
> (Cenomanian=E2=80=93Turonian) portion of the Winton Formation, Lark Quarr=
y,
> central-western Queensland, Australia: 3D photogrammetric analysis
> renders the =E2=80=98stampede trigger=E2=80=99 scenario unlikely.
> Cretaceous Research 51: 186=E2=80=93207
> DOI: 10.1016/j.cretres.2014.06.003
> http://www.sciencedirect.com/science/article/pii/S0195667114001141
>
>
>
> Highlights
> The largest Lark Quarry dinosaur tracks were examined using 3D protocols.
> Many track specimens indicate only minor deterioration since excavation.
> Most original outlines do not resemble actual track morphology.
> Overprinted traces suggest long time lags between large and many small
> trackmakers.
> Track succession allows for no interaction amid these different sized
> trackmakers.
>
>
>
> Abstract
> The largest dinosaurian tracks at Lark Quarry, central-western
> Queensland, Australia, were re-examined using revised analytical
> protocols that incorporate three-dimensional (3D) structure.
> Comparisons were made with archival photographs, replica specimens (c.
> 1977) and the in situ tracks (2013) to account for changes to the
> track surface. Damage caused both during and after the excavation of
> the tracks was evident, and in cases where the archival photographs
> and 1970's replicas strongly differ from the in situ tracks, it is
> apparent that restoration has modified the original track morphology.
>
> Even after accounting for recent damage and alteration, several of the
> track morphologies obtained from new 3D evaluation models differ
> considerably from the track outlines that were published in the
> original description of the site. Compared with the new set of
> representations, some of the original outlines seem to represent
> simpler, stylized versions of the tracks. A number of the original
> outlines are >20% larger than the in situ tracks, while others appear
> to incorporate cracks as part of the margin of digit impressions.
> Overall, the best-preserved tracks show blunt digit impressions,
> reaffirming the idea that the trackmaker was a large ornithopod and
> supporting a reassignment to cf. Iguanodontipus. The new analysis also
> reveals the nature of the displacement rims associated with the
> tracks, and the overprinting of these rims by other ichnites=E2=80=94init=
ially
> by tool marks (presumably caused by floating vegetation) and then by
> other dinosaurian tracks (assignable to Wintonopus latomorum). In the
> context of these observations, we see no evidence for an interaction
> between the cf. Iguanodontipus trackmaker and the smaller-bodied W.
> latomorum trackmakers, as neither can be inferred to have been present
> at the tracksite at, or even close to the same time. Similarly, there
> is no evidence to support the idea that the approach of the cf.
> Iguanodontipus trackmaker in some way triggered the movement of the W.
> latomorum trackmakers. Rather than a snap-shot of dinosaurian
> =E2=80=98stampede=E2=80=99, this study supports the idea that Lark Quarry=
 most likely
> represents a complex time-averaged assemblage of multiple dinosaurian
> ichnites, preserved over an extended period of time (hours to days)
> and bracketed by discrete phases of trackmaker activity and
> fluctuations in water depth.
>



--=20
Dr. Stephen Poropat

Postdoctoral Research Fellow
Uppsala University
Villav=C3=A4gen 16
SE-752 36 Uppsala
Sweden

Research Associate
Australian Age of Dinosaurs
PO Box 408
Winton 4735
Australia

--047d7b5d4e8af98fc904fdb7e211
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*         ---REMAINDER OF MESSAGE TRUNCATED---            *
*     This post contains a forbidden message format       *
*  (such as an attached file, a v-card, HTML formatting)  *
*    This Mail List at USC.EDU only accepts PLAIN TEXT    *
* If your postings display this message your mail program *
* is not set to send PLAIN TEXT ONLY and needs adjusting  *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

--047d7b5d4e8af98fc904fdb7e211--