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Re: What did Spinosaurus eat? New species of Lepidotes found
Of potential interest regarding secondary diving characters in birds, it turns
out that the cortical bone area of the humerus is over 50% at midshaft in
nearly all diving birds, but virtually none of the non-divers (even pelagic
taxa that only surface feed). Also curious is the observation that relative
bone strength of the humerus (corrected for moment arm length) is not elevated
in wing-propelled diving birds, except for penguins - where it is greatly
elevated. Go figure.
I admit that this is a bit of a selfish plug (the papers in question are Habib
and Ruff, 2008 and Habib, 2010) but it seemed relevant. Cheers!
Sent from my iPhone
On Feb 22, 2011, at 4:39 PM, "Dann Pigdon" <firstname.lastname@example.org> wrote:
> On Tue, Feb 22nd, 2011 at 5:00 PM, Tim Williams <email@example.com> wrote:
>> Dann Pigdon <firstname.lastname@example.org> wrote:
>>> I imagine that non-avian theropods would have had similar problems where
>>> diving was
>>> with their avian-style respiratory systems. Perhaps large theropods were
>>> prevented from
>>> habitual divers because of their inherant bouyancy.
>> Apparently _Hesperornis_ overcame its inherent buoyancy by
>> pachyostosis (in this case, developing thicker bone walls). Same for
>> the putative loon _Polarornis_. For example, in _Polarornis_ the
>> average bone wall thickness is 37% of its diameter, which is even
>> higher than the emperor penguin (_Aptenodytes forsteri_). The
>> red-throated loon (_Gavia stellata_) has a relative bone wall
>> thickness of only 15%.
>> So the natural buoyancy of non-avian theropods could similarly have
>> been overcome by making bones heavier (such as by being
>> thicker-walled). Pachyostosis (including osteosclerosis) is a
>> strategy adopted by many tetrapods that returned to water.
> Given that the vast majority of non-avian theropods were dedicated cursors
> (even at large sizes),
> would the thickening of bones effect terrestrial locomotion? Would it make
> the bones more liable to
> breakage, for instance, or would it significantly slow the animal down? Most
> aquatic avians don't do
> much in the way of running (a brisk waddle is usually their limit).
> Birds also had the initial advantage of two separate locomotory systems. Some
> aquatic birds use
> their forelimbs for propulsion, while a few primarily use their hindlimbs.
> Early aquatic birds could
> have coopted one means of locomotion for aquatic propulsion, while still
> having another to fall back
> on when out of the water. Many non-avian theropods didn't have this luxury -
> and even those
> with 'wings' probably weren't using them as a primary means of locomotion.
> Perhaps the transition
> to a largely aquatic lifestyle in theropods required well developed powered
> flight first (even if it was
> later lost)?
> Dann Pigdon
> Spatial Data Analyst Australian Dinosaurs
> Melbourne, Australia http://home.alphalink.com.au/~dannj