[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Microraptor also ate fish
Don Ohmes wrote-
> If an animal has the tools to catch live fish, predation is a much reliable
> method of obtaining a
> given quantity of food than scavenging, special conditions like anoxic events
Finally, we actually a possible argument for parsimony besides Xing et al.'s
"short spoilage time". Now, do we actually know that living animals capable of
catching fish eat more fish they caught themselves than fish they scavenged? I
think this isn't so clear cut. A specialized fishing animal like a skimmer,
sure. A more generalist aquatic predator like a heron, probably. But what
about something even more generalist like a gull? Do gulls kill more fish than
they scavenge? I wouldn't feel confident saying yes. Is there literature out
there on this?
Regarding anoxic events, aren't they supposed to be very common in the Jehol
habitat, and indeed the very reason specimens are preserved so well and so many
aerial taxa are preserved? And if that's true, surely it would influence any
calculation for fish scavenging being parsimonious.
In any case, THESE are the kinds of things that should have been discussed in
the paper (and prior 'theropod stomach contents equal hunting/scavenging'
Tim Williams wrote-
> > I note you didn't even reply to my single Ornithomimus footprint analogy.
> > What makes the
> > situations different in your eyes?
> The _Ornithomimus_ analogy struck me as a non sequitur. A single
> footprint is just that - something we might expect of any terrestrial
> theropod. By contrast, prey preference may vary between individual
> taxa. These prey preferences are determined by adaptations that may
> differentiate these taxa.
So perhaps our difference all along is that eating fish is something I expect
of just about any terrestrial theropod. If Baryonyx can do it and
Confuciusornis can do it and even baby Scipionyx can do it, then I expect
Microraptor to have eaten fish. Ditto for lepidosaurs. We don't have any
published Microraptors with lepidosaurs in their stomachs, but giv
ipionyx, Compsognathus and Oviraptor, I don't think "Microraptor found with
lizard in belly" would be a big story, nor would I think it justified an
attempt at finding lizard-hunting specializations. Now if we found 90% of all
stomach content in Microraptor were fish, or were lizards, then it would start
> > None of what you said makes predation of the fish more parsimonious. To be
> > so, it would have
> > to explain the
> > data better than scavenging, and you admit in the last paragraph scavenging
> > fish requires no
> > special
> > morphology for a theropod. So hunting fits its morphology well, and
> > scavenging fits its
> > morphology well.
> Not quite. Hunting of certain prey "fits" what is specifically
> inferred based on morphology. Opportunistic scavenging does not "fit"
> any specific morphology (beyond what one might expect of a predator or
> carnivore). So it difficult to frame a morphology-based hypothesis
> that an animal was an opportunistic scavenger.
But fitting a more specific morphology doesn't make it any more parsimonious
than fitting the more generalized morphology of "terrestrial carnivore". Both
aspects of morphology are equally present in Microraptor.
> Let's say we propose a hypothesis regarding prey preference based on a
> predator's morphology, such as that the predator was a fish-eater
> (piscivore). We then find a specimen of this predator that has a fish
> inside its abdominal cavity. I'd say we have evidence that is
> consistent with this hypothesis. Not hard proof; I won't go that far.
> One swallow doesn't make a summer, and one ingested fish doesn't make
> a piscivorous theropod. But it's a start.
We must have different concepts of parsimony here, because I feel we're making
the same points over again and expecting the other to agree.
To try a phylogenetic analogy, say you have a theropod and you propose a
hypothesis of relationship based on its morphology, such as that the theropod
is a dromaeosaurid. Then you find a specimen of it that preserves feathers.
aurid hypothesis. I say sure, BUT I point out the morphology also fits with it
being a troodontid, as all of your dromaeosaurid features are also found in
troodontids. And troodontids have feathers too, so the feathered specimen is
also consistent with that. Thus neither hypothesis is more parsimonious.
What you have to do to support the dromaeosaurid hypothesis as more
parsimonious is give features that are more congruent with it being a
dromaeosaurid than it being a troodontid. And what you have to do to support
the predation hypothesis is to give features that are more congruent with that
fish being caught instead of being scavenged. Don's actually done that above,
proposing a predator capable of catching fish will prey on more fish than it
scavenges. But you seem to think pointing out that Microraptor probably could
and did catch fish somehow influences the liklihood of it scavenging them.
> > Not that the Confuciusornis / wood duck thing has anything to do with Xing
> > et al., since they
> > don't make the Sinocalliopteryx point you did, but... are wood ducks' legs
> > actually notably
> > shorter than Confuciusornis', or do they just look that way due to feathers
> > making the body
> > seem bigger and only the tarsometatarsi being exposed? Also, Confuciusornis
> > pedal unguals
> > are much larger and more curved than the wood duck's, so I don't see why
> > you think the latter
> > are better adapted for perching.
> This is one example of why I hesitate to apply the word "bird" to any
> avialan that lies outside the crown group. _Confuciusornis_ was a
> long way from being a crown avian, and it was nothing like a duck.
> Aside from both being pygostylian avialans, that is. So just because
> a certain species of duck can do something (perch) without the aid of
> an enlarged hallux doesn't mean any basal avialan can do it. Again,
> I'm tying certain behaviors to specific adaptations here. Even among
> crown birds, wood ducks are exceptional in being perchers that have
> short halluces. But perching is achieved in oth
> that the gross morphology (including the very short effective
> hindlimb, and forwardly displaced center of mass) has something to do
> with maintaining a stable posture when the bird is sitting on a
> branch. Given the wide gulf in overall proportions between
> _Confuciusornis_ and a wood duck, extrapolating the behavior of the
> latter to the former is drawing a long bow indeed, IMHO.
If we're going to go that route, why are we even bothering to compare ungual
curvature and phalangeal proportions to determine Confuciusornis' habits?
There's obviously some level of comparison, and you could come up with features
arguing for "my" side just as easily- Maybe confuciusornithids' different
standing posture, ability to hold on with hands, heavier gut if they were
herbivorous, longer hallux, assumed non-webbed feet and larger claws etc., etc.
counteract the supposed shorter hindlimb and forward center of mass advantages
of the wood duck. But if we just say these differences don't allow comparison,
we won't get anywhere.