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

RE: Velociraptor scavenged azhdarchid pterosaur



A lot of good discussion on this.  With the revelation that the supposed long 
bone or distal wing phalanx is actually a small semicylindrical fragment and 
that the pterosaur weighed 3/4ths as much as the theropod (and that in itself 
is highly uncertain), I don't see how scavenging can be favored, let alone 
allowed to be the supposedly novel concluding sentence of the abstract.

Mike Habib wrote-

> 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?

I agree with Poropat's responses, though I would add that whatever size 
difference should be accepted as indicating scavenging needs to be backed up 
with data from modern animals like monitors, crocodilians and carnivorous 
birds.  These would also be the taxa to check for differences in stomach bone 
content after predating vs. scavenging.  Of course none of these animals were 
very similar to dromaeosaurids in their ability and method of dismembering prey 
(no teeth for birds, conical serrationless teeth and death rolls in crocs, no 
manipulative forearms in any), but it should give us some real data to work 
with unlike intuitions like a predating animal won't usually swallow a bone 
fragment.  Then to the extent that a case like this matched either predating or 
scavenging, we could say the theropod was however likelier to be doing either.

In addition to Poropat's ideas, I'd say bite marks or embedded teeth of a small 
animal on a significantly larger animal would be good evidence for scavenging.  
Also if we had two different species' feeding traces on one carcass, that would 
show at least one of them scavenged.

Dan Chure wrote-

> Seriously, I am interested in whatever evidence you might have in 
> interpreting  the Protoceratops-Velociraptor specimen as something other 
> than an attempted predation event (maybe going badly for the predator) 
> preserved in progress. If there are alternative explanations for that 
> specimen other than predation and the evidence is such that we cannot 
> choose between the alternatives, then the topic of predation in 
> dinosaurs should probably just be abandoned as a research effort. If we 
> cannot figure out what the hell is going on in such a spectacular specimen 
> as that of the V-P, then why spend any time with tooth marks, 
> bone fragments within rib cages, or any other such material.

Osmolska (1993) noted that the Protoceratops lacks forelimbs and has displaced 
scapulocoracoids, perhaps suggesting it was already dead and dismembered when 
the Velociraptor got tangled in it and buried.  Then again, the Protoceratops 
does seem to be biting the Velociraptor's wing.  So I agree with Chure that if 
even the Fighting Dinosaurs can be ambiguous, we're not going to be able to say 
much at all about the present specimen.

Mark Witton wrote- "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?"
"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."

These statements are especially interesting and damning. Since Witton was a 
reviewer, how did the paper make it through review without these issues being 
considered?  Similarly, Hone et al. state "The dromaeosaur was consuming bone 
(perhaps with some trace flesh attached) presumably because there was little 
else to eat on the carcass...", but this is completely unsupported and indeed, 
unsupportable.  It could have had a belly full of flesh in addition to this 
bone fragment, and the resulting fossil would be identical.  

Ben Creisler wrote- "A obvious question is why the Velociraptor happened to 
drop dead right after eating the pterosaur bones."

I don't see this as problematic at all.  If we're assuming theropods had high 
metabolisms and thus needed to eat often, they would be relatively likely to 
have just eaten if buried in a sandstorm (since this specimen was found in 
eolian deposits).  The authors do state "The animal was injured or recovering 
from an injury at the time of death with one broken dorsal rib showing signs of 
regrowth", but surely since there's regrowth, the injury could have healed by 
the time of death too.  No doubt a pathologist could make a more detailed 
pronouncement.

Mickey Mortimer