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

RE: How Pelicans learn to fish



Jaime,

Briefly: I agree with you that biomechanics are important, but surely
the best approach to take when considering the habits of an extinct
animal is a holistic one where all available and relevant evidence is
taken into account? To continue with our Pteranodon example, we can
consider the number of fossils in the Niobrara that are clearly
terrestrially-derived (a handful of dinosaurs, none of which, AFAIK, are
complete) compared to the thousands of Pteranodon that, in many cases,
are associated, complete specimens. I suppose it is possible that all of
these individuals were washed out to sea along with the dinos, but the
numbers suggest this is unlikely. 

And yes, there's the biomechanical evidence that Pteranodon was a
supreme flier comparable in ability to soaring marine birds but, from a
wing ecomoprhology perspective, inconsistent with what we would predict
in a terrestrial flier. No-one has ever done detailed studies on their
terrestrial limb mechanics (save for the work with Robodactylus, I
suppose, but I have my reservations about that:
http://pterosaur-net.blogspot.com/2010/10/pterosaur-books-to-know-and-love-part-2.html)
but there are reasoned considerations in print that suggest their
terrestrial ability was limited. These, coupled with the fact that we
have marine fish as gut content of Pteranodon, suggests that the data
points at a pelagic existence for this pterosaur.  

And while quantification of as many mechanical parameters as possible is
good, I think we can all agree that some basic application of everyday
mechanical experience can be applied to some fossils, too. We all know
from day-to-day existence that, on the whole, small, thin objects will
break easier than chunky, robust ones. We can therefore, at least on a
qualitative, comparative level, say if the anatomy of some forms is more
suited for one thing than another. Darren and I did this with
azhdarchids and had our findings supported by the mechanical testing of
Humphries et al. (2007) who used both qualitative and quantitaive
mechanics to cast doubt on skim-feeding pterosaurs (and we looked at a
lot more than the jaw joint of Rynchops, too boot). Hence, while putting
numbers to mechanical observations is obviously desirable, but I don't
think we should sell our own observations short. 

Finally, in my view, applying a strictly mechanical approach to fossil
animals is a dangerous game. The sauropod examples you cite are a good
example: our biomechanical models of sauropod necks differ drastically,
as Mike Taylor has already pointed out, from what we see in living
animals. Simply modelling animal bones as beams or whatever to assess
their strength is one thing, but attempting to accurately model complex
movements and postures when we barely understand the same in living
animals is a little foolhardy, surely? What I particularly like about
the Taylor et al. paper is that it concedes that there's still a lot to
learn about how animals work: they suggest we really need to get up to
speed with the likes of neck arthrology in modern taxa before we start
seriously modelling those of fossil animals. In the mean time, they
suggest applying rules of uniformitarianism and parsimony in their
place, a finding I agree with entirely. It's not as clever as a detailed
biomechanical analysis, but I reckon it's smarter.

Right, hope that makes sense. Back to work.

Mark

--

Dr. Mark Witton

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 check out:

- Pterosaur.Net: www.pterosaur.net
- The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
- My pterosaur artwork: www.flickr.com/photos/markwitton
>>> Jaime Headden  04/11/10 1:14 PM >>>

Mark and the List,

  I may have been too blunt in the first (or too subtle), so I will
explain in a little more context.

  1. In the Niobrara, all fossils are found in marine sediments. This
includes all so-called terrestrial fossils, such as nodosaurs. Now, it
may be arguable to infer some form of aquatic viability to nodosaurs,
but for the most part the limb anatomy implies these taxa are firmly
terrestrial, and yet they are all found in marine sediments. This is
instructive for a variety of reasons, the first among them being that
the Niobrara is exceptionally good at preservation, and that the second
being that the environment is conducive to pulling nearshore or
shore-based carcasses into waters several to a hundred kilometers from
shore. This should be no different were the animal a nodosaur (an
apparent terrestrial herbivore), a hesperornithiform (a bird with very
limited flying ability whatsoever, and likely a near-shore denizen) or a
pteranodontid.

  2. Some researchers, when comparing taxa to one another, tend to look
on an archetypal level, or a elemental level, separating their
perspective for the forest or the tree, respectively. In this case,
looking at an animal, we can attempt to assess it on the basis of a host
of features that seem to look like animal X, or we take a specific
feature -- element Y -- and see what animals A-Z have element Y, and
base our comparisons on ecology (and sometimes evolution) on the basis
of this comparison. In my rather not-so-humble perspective, the best
model may be the one that derives a lot of the second into the first,
comparing a host of elements into a broad spectrum of biology. This
allows us to make a broad assumption for animal X to be like animal Z,
because of elements A-Z.

  For the most part, I think a lot of the discussion on the paleobiology
of birds, pterosaurs, and other taxa comes across as this third,
reasoned approach. But as I may have occassionally pointed out on my own
blog (below -- currently suffering from new computer syndrome, forgive
me for not handling or updating recently), some authors have slipped
into either the archetypal or the elemental model of comparison, and
argued against the third, integrated model in some fashion, or to use
the first to fight the second (and vice versa). This has included birds,
pterosaurs, and various other archosaurian animals. My favorite retort
is "Sauropods are not giraffes." So, too, are "Pterosaurs are not
birds," "birds are not special," etc.

  3. So, in this perspective, I casually alluded to some research and
made a few very bold statements tied directly to these; both in
challenge and in plaintive appraisal. This includes the argument that
azhdarchids are preferentially terrestrial and were like maribou storks
(from Mssrs. Witton and Naish), or that azhdarchid pterosaurs could not
skim feed because one skim-feeder had a specialized jaw joint (Mssrs.
Witton and Naish, again), or that sauropods were correctly highly
elevated in their neck posture because a range of other, often quite
much smaller animals have elevated necks (Mssrs. Taylor, Wedel and
Naish), that birds are powered fliers, that *archaeopterys* is a
devolving bird, and that as a bird must have been a powered flier (Mssr.
Paul). I have been openly critical of many of these papers not on the
basis of some special expertise or quality of work which is being
rejected or that I can produce to reject, but on the basis of logic.

  My argument is plain: None of these have made direct assessment of the
feeding or stature effects of each of the organisms involved, but
through attempts at comparisons without direct examination of the
functional concerns of the animals involved. Let's break these down, and
I will conclude this long post.

  4.

  A. Preferential, even exclusive, habitats of the locality in which a
fossil is found is only indicative of the location in which said fossil
was deposited; it does not always indicate place of death (this requires
additional data), or even generalized preference of habitat (this
requires a load of what amounts to ecological data, and that includes
feeding traces, coprolites, any other -ite indicating a direct
preference for food, etc. 

  B. I understand the paper in question
(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0002271)
lists out a large number of other features, but again these data suffer
other problems, including comparing the jaw joint of an azhdarchid to
that of *Rhynchops*(, and concluding the former cannot skim-feed -- this
is only true if skim-feeding is defined as that thing which *Rhynchops*
(and only it does), which is a logical problem that ignores any other
possible model for the term or method of "skim-feeding." I don't
actually know about the data to as large an extent as some of the
particulars in the issue, but I take the issue of what is essentially
indirect comparison broadly: The authors do not show that the
specialized jaw of *Rhynchops* is required for skim-feeding in that
manner (as, indeed, they remark on another bird that skim-feeds that
lacks said specialized jaw anatomy), and this only tells me that the
initial claim is merely doubted, but used as a hammer nonetheless.

  C. In a more interesting set of discussions, the posture of sauropod
necks was presented in a long stream of public airings of disapproval by
accredited scientists, all of whom are well-respected and knowledgeable
of their preferential taxa, but little work in print on the subject.
(http://www.app.pan.pl/archive/published/app54/app54-213.pdf -- PDF
link, open at your peril!) is a paper on the conclusive argument that
sauropod necks are like other terrestrial diapsid necks in that they are
tended to elevate at or around 45 degrees, unerringly. This is
problematic for three reasons: 

  1) The primary animals used in the analysis (the one used to
demonstrate the incohesiveness of Stevens and Parrish Osteological
Neutral Pose) is a mammal which, in a comment on SV-PoW!, Kent Stevens
was agast at the authors comparing sauropod necks to that of a mammal
(these differing in a large number of fantastically different ways,
including the structure of the zygapophyses, the centra, the
intervertebral discs, and in fact the very model of the suspension of
the head from an proximally elevated system of muscles and tendons found
nowhere else in diapsids -- some birds have a similar system, and
include suspended necks, including of all things *Rhynchops*, fairely
notable for the fantastic number of tendons that extend from several
discontinuous series of cervicals between head and dorsum).

  2) The extrapolation to a broad set of taxa across Diapsida, to show
how universal the neck posture is (conceding that some organisms differ
markedly due to habitat, namely, the aquatic kind).

  3) That for some reason, size doesn't matter here, that sauropods
having the largest, longest necks of any terrestrial animal alive or not
has no influence on this contraint (especially as the largest
terrestrial vertebrates alive have fantastically short necks and huge
heads).

  None of this is supported through direct analysis of the sauropod
cervical system, rather only through inferences of the animals upon
which the study is based. We can support that the unusual neck anatomy
of some sauropods (like dicraeosaurids) or the bizarre cranial form of
*Nigersaurus taqueti* requires us to make careful such broad-stroke
comparisons, and even more so when studies have been published that
alter the envelope to which sauropods can extend their neck in extremes
or safe levels of stress on the joints, and that these shift the numbers
upwards (for *Brachiosaurus brancai* = *Giraffatitan*) or downwards
(*Euhelopus zdanksyi*); analysis of different groups of very-long necks
sauropods show that they differ broadly in cranial form and dental
apparatus, providing us with a missing ecological signal the authors of
the study may have used to calibrate their work; and finally, a
potential rejection of the use of biomechanical modeling for the sake of
broad-stroke painting of sauropods as ... well ... giraffes.

  (With due respect to the authors, though, they do make strong
comparison to a (presumably domesticated) chicken, extending their
practical testing of dry, bone-only cervical and cervico-cranial
articulation to a mammal AND a bird, and unpublished and referenced work
supporting a broader collection of living animals examined under
radiological means.)

  D. Birds are awesome in their variety but, and in no due disrespect to
bird watchers or ornithologist, they aren't that special. Some of the
things they do may be, but recent semi-scientific work produced by a
populoar author and illustrator and scientist has challenged various
apparent biomechanical or straight up osteological comparative work with
an argument that a wing-like limb must operate as a wing. This is an
archetypal thought, extending back to Aristotle, reminding us that all
Creation is special and particular, and that purpose is driven in form
due to evolutionary need, or special force. It is argued, similar need
from a similar plan should conserve the variety of derivatives possible
in its efficiency (Law of Conservation of Energy and all). Lockely has
recently published a few pieces making the argument that there is
conserved archetypism in the animal kingdom, and that some biological
trends are natural, such that large-headed, large-bodied theropods
should look like tyrannosaurs. In that vein, Paul argues that
*Archaeopteryx* looks like a bird, is a bird, birds can fly, thus
*Archaeopteryx* can fly. Maybe not very well, but nonetheless.

  ***

  All of these arguments require logic that is missing. As a pragmatist,
as a conservative thinker (moderate politically, liberal ideologically),
and one with an eye toward biomechanics as MY field, I tend to look on
the practical testing side of things, and I go about thinking how I
would test all of these hypotheses, and I cannot using the processes the
authors do. Again, practical. I want to examine the various forces and
modeling that describes an organism's flying, broad across the spectrum
of fliers, and examine where my particular organism (proto-bird or
pterosaur) might most closely fit, then examine that in the context of
what is really quite a large host of additional data, both phylogenetic
and ecologic. If an animal is argued to hold its posture in a certain
way, I ask "How long?" "Why?" "What else is it doing?" "How do I
determine extent, range, and performance of said posture?" "Are there
other viable alternatives?" Sadly, some do not ask these questions. I am
exceptionally interested in one particular part of biomechanics, and
that's the study of dietary systems and especially oral anatomy, so when
I see a potentially vital part of the various questions of pterosaur or
sauropod posture/feeding, and many of these questions are ignored or
lost in a sea of what the authors may feel are vitally more important
questions, I am bemused.



  So when I talk about terrestrial *Pteranodon*, it's really about using
 conclusions that have little to do with modeling the anatomy and 
ecology through as direct means as possible, but about pulling in the 
various little "signals" to put forward what is probably not a very 
likely theory; and were I to publish this, I might be more severely 
laughed at than is due the consideration. It is plausible, but unlikely.
 But plausible.

  To Mark Witton's credit and in no criticism of the others mentioned
here, the first Witton/Naish paper mentioned above is a great paper,
probably the best among the works I've so far talked about. It really
does approach the question from a large number of angles, and I have
little doubt to the methods' authenticity. Mark showcased his
terrestrial-wtalker, sauropod-baby-killer theory in London earlier this
year, and I am sure it got a large number of people interested in the
subject of paleontology who may not have been so immediately intrigued
before. But the problem therein is that this is a premise being
chosecased without a substantive amoutn  of data supporting it. When
contesting the theory of jaw function, the authors do not actually model
the jaw function, merely poke holes into a particular comparison and
declared the argument null. This seems illogical, and it raises a red
flag, as it did in all of these other works I've mentioned. I keep a
quote by Medawar in my sig because it reminds me of this topic, that
none of us are immune to bias to a particular perception or idea. The
more we are aware of it, the better we are armed to fight it. This is
what I think "science" is.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

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

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a
Billion Backs)





----------------------------------------
> Date: Thu, 4 Nov 2010 10:17:03 +0000
> From: Mark.Witton@port.ac.uk
> To: dinosaur@usc.edu
> Subject: RE: How Pelicans learn to fish
>
> Jaime,
>
> Not sure about the ideas of terrestrialised Pteranodon: over 1200
> fossils of it have been found in the middle of the Western Interior
> seaway and, AFAIK, not one has been found in a terrestrial deposit.
I'm
> wary of using the sedimentological contexts of large flying
vertebrates
> as indicators of habits (though have done so in print in the past: I
> think it can be done if we're careful) but Pteranodon really is skewed
> towards marine settings: we're special pleading, big-time, if we want
> this critter walking around on land.
>
> I can't see the bauplan of Pteranodon working too well for Pteranodon
on
> land, either. There's that massive overbite on the jaws that would
make
> eating anything small a real issue, and the slenderness of the
Pterandon
> skull wouldn't lend itself to large, feisty prey items (though your
> point about the skull being enlarged for signalling may be right here:
> the overbite is larger in presumed males). Plus, their limbs really
> aren't adjusted for walking around: the forelimbs are so much longer
> than the hindlimbs that their terrestrial movement would be far more
> hampered than that of other pterosaurs. Probing isn't too likely in my
> view: deriving the full benefit of their jaw curvature would require
> sticking, in the largest Pteranodon, about 60 cm of jaw into sediment,
a
> big issue when the skull expands in all dimensions along the jaw
length.
> Plus, along with the problems of the overbire, the rostrum is very
thin
> but tall: sticking it into sediment may risk breaking it
> (Dsungaripterus, by contrast, is a better candidate for a prober,
having
> shorter jaw curvature and a more robust, powerful skull). Hence, while
> you're right about the sample size of Pteranodon gut content being
small
> (one confirmed case, plus some associated fish debris with some
> skeletons that, possibly, could be mere marine detritus), I expect
it's
> probably representative of typical Pteranodon fodder: little fish
> wouldn't tax the slender skull and could easily be grabbed from the
> water column, a place where that overbite doesn't get in the way.
>
> Mark
>
> --
>
> Dr. Mark Witton
>
> 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 check out:
>
> - Pterosaur.Net: www.pterosaur.net
> - The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
> - My pterosaur artwork: www.flickr.com/photos/markwitton
> >>> Jaime Headden 03/11/10 1:51 PM >>>
>
> Or we can take a cue from another direction and say that because the
> skull is deep and triangular, and looks like a stork, it was feeding
on
> larger, more selective prey than opportunistic fishing in this manner.
> Small amounts of fish may mean not as much fish feeding, after all
> (although I am sure we've only been able to derive limited information
> from limited specimens in which limited amounts of gut contents are
> known -- correct me if the sampling is much higher in resolution than
> this). Perhaps *Pteranodon longiceps* was a terrestrial carnivore, as
> Witton and Naish suggested for another very-large-headed pterosaur
> group. Moreover, due to the massively outsized skull of
pteranodontids,
> one may assume that head-based strategies for prey acquisition were
the
> norm, and that in this realm of comparison that they were incomparable
> to a large number of living taxa (including birds) making comparisons
> problematic (just as the relatively inflexible neck of azhdarchids
> impairs comparison to storks).
>
> One thing I do not recall (precisely, but may have seen in print
> somewhere) is that the slight upturn to the beak and the outsized
length
> of the upper beak to the mandible indicates a functional distinction
to
> some typical pterosaurs, which have relatively even lengths in these
two
> cranial segments. Moreover, the upturn can indicate "prying" behavior
> (impairing fossil evidence of meals) -- much as has been suggested for
> *Dsungaripterus weii* -- while the outsized upper to lower could
> actually make the skull effectively a giant signaling device, and have
> very little, if anything, to do with feeding.
>
> Cheers,
>
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language
or
> his new way of looking at things." --- Zapp Brannigan (Beast With a
> Billion Backs)
>
>
>
>
>
> ----------------------------------------
> > Date: Wed, 3 Nov 2010 10:07:12 +0000
> > From: Mark.Witton@port.ac.uk
> > To: dinosaur@usc.edu
> > Subject: Re: How Pelicans learn to fish
> >
> > "Much has been written and speculated regarding pterosaur flying,
but
> > what about smacking the water?"
> >
> > Lots of folks have suggested Pteranodon may have plunged dive, with
> > Chris Bennett most recently noting that the skeleton of Pteranodon
is
> no
> > more fragile than that of Pelecanus and that diving from heights of
10
> m
> > or so was possible. However, the regurgitated gut content of
> Pteranodon
> > suggests that pretty dinky fish were being eaten, and Pteranodon has
a
> > particularly long, narrow skull that may be ill suited to grabbing
> > mouthfuls of small fish in a pelican-like manner (indeed, you can
> ignore
> > the many claims that pterosaur and pelican bills are anything alike:
> the
> > little helical jaw joint of pterosaurs does allow for slight
> expansion,
> > but it's a million miles away from the multi-hinged, distensible
> > mandibles of pelicans). I wonder if Pteranodon was feeding in a
> slightly
> > more careful manner, perhaps alighting on the water surface or
> something
> > like that.
> >
> > Mark
> >
> > Mike Habib 03/11/10 12:41 AM >>>
> > No specific ones that I know of, but I haven't looked carefully. In
> > both cases the skull is large and largely thinned-walled, but that
> > probably isn't a diving correlate, per se. Maybe someone else here
has
> > looked at that in more detail.
> >
> > --Mike H.
> >
> >
> > On Nov 2, 2010, at 7:47 PM, Dan Chure wrote:
> >
> > > Any structural convergences in the skull?
> > >
> > > Dan
> > >
> > > On 11/2/2010 5:21 PM, Mike Habib wrote:
> > >> The only diving birds that fold back the wings in a "knife"
> position
> > are gannets and boobies (i.e. sulidae). Pelicans actually don't tuck
> > their wings all that far back on dives; I doubt it's beyond the
normal
> > joint excursion for a modern bird.
> > >>
> > >> One bit of interest, though, is that the ratio of bone wall
> thickness
> > to total bone diameter in pelicans is very similar to that in
derived
> > pterodactyloids. It's about the same as Pteranodon, for example.
> > >>
> > >> Cheers,
> > >>
> > >> --Mike Habib
> > >>
> > >>
> > >> On Nov 2, 2010, at 7:13 PM, Dan Chure wrote:
> > >>
> > --
> >
> > Dr. Mark Witton
> >
> > 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 check out:
> >
> > - Pterosaur.Net: www.pterosaur.net
> > - The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
> > - My pterosaur artwork: www.flickr.com/photos/markwitton
> > >>> Are there any osteological correlates to pelican diving
behavior?
> > One would be joints that allow the wings to be rotated backwards,
but
> do
> > all diving birds do that or does diving occur in other ways in other
> > birds?
> > >>>
> > >>> Dan
> > >>>
> > >>>
> > >>> On 11/2/2010 2:05 PM, Richard W. Travsky wrote:
> > >>>> Of course the first thing I thought of was pterosaurs...
> > >>>>
> > >>>> http://www.nytimes.com/2010/10/26/science/26qna.html
> > >>>>
> > >>>> Q. How do pelicans learn to dive for fish?
> > >>>>
> > >>>> A. Young pelicans learn to feed themselves through a
combination
> of
> > trial and error, imitation of adult birds and instinct, bird experts
> > suggest.
> > >>>>
> > >>>> In the United States, the Eastern brown pelican (Pelecanus
> > occidentalis carolinensis) and the California brown pelican
(Pelecanus
> > occidentalis californicus) make dives onto schooling fish from
> > impressive heights or float on the surface to scavenge fish. A dive
> from
> > 30 to 60 feet up, or even higher, hits the water with considerable
> > force. Fish a few feet below the surface are scooped up, and water
> > drains from the sides of the pouch. They tilt their heads back and
> > swallow on the spot.
> > >>>>
> > >>>> For young pelicans, some early experience in diving for fish
> comes
> > during their time in the nest, when they graduate from feeding on
> > half-digested fish bits regurgitated by their generous parents to
> > retrieving fish from the famously capacious pouched parental bills
and
> > even their gullets. The nestlings may dive in shoulder deep to make
> the
> > parents disgorge fish. Pelicans are well fed in the nest for 9 to 11
> > weeks, by which time they are fully feathered and ready to go out on
> > their own.
> > >>>>
> > >>>> Their diving success rate is highly variable and depends on
> > experience. Adult California brown pelicans bring up fish from
around
> > two-thirds of their dives, while novices appear to have a lot of
> > trouble; fewer than half survive their first year out of the nest.
> > >>>>
> > >>>>
> > >>>>
> > >>>> Didn't know the mortality rate was that high.
> > >>>>
> > >>>> Much has been written and speculated regarding pterosaur
flying,
> > but
> > >>>> what about smacking the water?
> > >>>>
> > >>>>
> > >>>
> > >> Michael Habib, M.S.
> > >> PhD. Candidate
> > >> Center for Functional Anatomy and Evolution
> > >> Johns Hopkins School of Medicine
> > >> 1830 E. Monument Street
> > >> Baltimore, MD 21205
> > >> (443) 280-0181
> > >> habib@jhmi.edu
> > >>
> > >>
> > >>
> > >>
> > >>
> > >
> > >
> >
> > Michael Habib, M.S.
> > PhD. Candidate
> > Center for Functional Anatomy and Evolution
> > Johns Hopkins School of Medicine
> > 1830 E. Monument Street
> > Baltimore, MD 21205
> > (443) 280-0181
> > habib@jhmi.edu
> >
> >
> >
> >
>
>