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Re: Velociraptor scavenged azhdarchid pterosaur



A 9 kg mass was deduced using the dataset from Witton 2008, I believe, with a 3 
m span Zhejiangopterus as a model. The paper does suggest a 3 m span for the 
pterosaur, so I'm fairly happy with that mass estimate myself (though I don't 
consider my work the last word on this at all, of course: there's still a lot 
to be done on pterosaur mass).

Re. evidence for scavenging vs. predation in the V. vs. P. paper: I am very 
sceptical of this myself (I did say so in my review of this paper). The 
pterosaur material described in the paper is a scrap of bone - 75 x 12 mm - so 
we have no idea what part of the body it represents. How do we know how large 
the pterosaur was if we don't even know what bone we've got? The paper tells us 
it was likely exceeded 100 mm in length: why should we assume that? Assuming it 
represents a limb bone of some kind, conservative wingspan estimates based on 
its proportions are 2 - 3.6 m. A 2 m span azhdarchid may weigh as little as 4-5 
kg, less than half of the Velociraptor in this instance. The authors of this 
paper favour a 3 m span for the animal, but do not say why this is the 
preferred span estimate. The relative masses of the two animals discussed in 
the paper is a critical part of the scavenging story, so it needs to be more 
substantially verified to give credence to their idea. If this paper favoured 
the lower (and more conservative) estimate, the body sizes of these two animals 
would be far more disparate and the scavenging argument weakened considerably. 
Alternatively, that scrap could represent a part of a larger bone from a giant 
pterosaur limb girdle or cranium, which would make the scavenging notion much 
stronger. We just don't know: it's a _scrap of bone_, so we need to be 
realistic about what stories it can tell us. 

There is also some borderline speculation in the paper (i.e. "While pterosaurs 
are light for their size, an active predator such as an azhdarchid... would be 
a difficult, and probably even dangerous, target from a young dromaeosaur"; "A 
bone of such diameter and length would presumably have been a challenge to 
consume.") that I find very troubling: how do we test the idea that 
Velociraptor found similarly-sized pterosaurs challenging to predate? Do we 
know how flexible the throat tissues of Velociraptor are (though, if they're 
anything like predatory birds, they would be very elastic, and a bone like this 
may not be hard to swallow at all)? Also, cats and komodo dragons, despite not 
being adapted to eating bone, ingest bony material – sometimes of large size – 
(Valkenburgh 1996; Montalvo et al. 2007; D’Amore et al. 2011) and are capable 
of disarticulating/breaking carcass skeletons on their own via pulling actions 
during feeding. It's been pointed out time and again that pterosaur bones are 
strong against bending and twisting, but are vulnerable to buckling, and may 
break easily when their owners are being devoured.  As Mickey has already 
pointed out, we don't know that this scrap of bone didn't merely get caught up 
in other, fleshier remains when the animals was feeding. Bottom line: what does 
a scrap of ingested bone actually tell us? It tells us that one animal ate 
another, but that may be all it really says without invoking a lot of rather 
tenuous assumptions.

That's my ultra-conservative two cents, anyway. I'm off to make my sofa into a 
little fort to defend myself from the backlash of people thinking I'm being 
overly critical*.

Mark

*Actually, I might just do that anyway, replies or not.  



--

Dr. Mark Witton
www.markwitton.com
Lecturer
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk

If pterosaurs are your thing, be sure to pop by:

- Pterosaur.Net: www.pterosaur.net
- The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
- My pterosaur artwork: www.flickr.com/photos/markwitton 


>>> "Habib, Michael" <MHabib@Chatham.edu> 04/03/2012 06:32 >>>
True, but that assumes that the "fighting dinosaurs" preserves a one-on-one 
predation attempt, which I personally doubt (actually, it may not be a 
predation attempt at all - consider that the Velociraptor appears to have been 
in the process of being mangled badly).  Incidentally, the 9kg mass for the 
azhdarchid in the new paper is probably too low by a fair margin (9kg is about 
the mass of a large albatross).  In any case, we cannot absolutely rule out 
predation, but it would still seem that scavenging would be the preferred 
hypothesis in this case.

This discussion/debate brings up an interesting question: what evidence should 
we, as paleontologists, require before tentatively accepting a scavenging 
hypothesis for a given preserved feeding event?  And conversely, what evidence 
should be required to tentatively accept a predation hypothesis?

--Mike Habib


On Mar 4, 2012, at 12:54 AM, Tim Williams wrote:

> Mickey Mortimer <mickey_mortimer111@msn.com> wrote:
> 
>> Scavenging's certainly possible, but since the closely related Deinonychus 
>> is generally accepted as predating Tenontosaurus (which is about as heavy
>> compared to Deinonychus as Quetzelcoatlus is compared to Velociraptor), I 
>> don't see how we can favor one hypothesis over another.  Sure I'm assuming
>> that the Velociraptor was found singly, but if Roach and Brinkman (2007) are 
>> correct that Deinonychus did not live in packs but merely aggregated to kill,
>> then a lone dromaeosaurid with parts of a large animal in its belly is just 
>> what we'd expect.
> 
> 
> 
> There's also the famous "fighting dinosaurs": _Velociraptor_ preserved
> in combat with _Protoceratops_.  The _Velociraptor_ (an adult) is
> estimated to have have weighed around 24 kg, the _Protoceratops_ at
> least that much.
> 
> 
> For the Hone &c study, the _Velociraptor_ was a sub-adult estimated to
> have tipped the scales at 13 kg.  The pterosaur is estimated to have
> weighed at least 9 kg.  So IMHO the contest between _Velociraptor_ and
> pterosaur would be less daunting than _Velociraptor_ vs
> _Protoceratops_.  Also, pterosaurs (even azhdarchids) were less adept
> on the ground than velociraptorines.  Would it really have been
> prohibitively difficult for a  _Velociraptor_ to attack an azhdarchid
> of comparable (or even lesser) body mass?  Even if the pterosaur
> weighed substantially more than the _Velociraptor_, predation still
> seems to be well within the realm of possibility.
> 
> 
> 
> 
> 
> Cheers
> 
> Tim

Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu 
(443) 280-0181