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Fwd: Spinosaurs show semi-aquatic oxygen isotopes

---------- Forwarded message ----------
From: Jocelyn Falconnet <j.falconnet@gmail.com>
Date: 2010/2/6
Subject: Re: Spinosaurs show semi-aquatic oxygen isotopes
To: augustoharo@gmail.com

Well, there are those big Allosaur-sized theropod swimming tracks in
Spain (Ezquerra et al., 2007), Utah (Milner et al., 2006), and
Connecticut (Rainforth & Howard, 2008), so it why not ! Just have a
look to extant mammals: bradypuses are good swimmers despite their
lazy reputation, elephants can swim across the sea from island to
island, hippos are fast runners (yeah, they are running instead of
swimming underwater), even kangaroos and wallibies have been reported
to be good swimmers - one of them has been seen going down the beach
in light surf for about 1/2 mile (here:
http://www.kangaroo-protection-coalition.com/kangaroo-swim.html) !!
Well, one may object that kangaroos and wallibies are much lighter
than a standard spinosaurid... That's always the problem with puzzling
groups having no extant analogous.

Regarding bone density, pachyostosis is mainly seen on
dorsals/thoracic ribs, and sometimes also on dorsal vertebrae of
animals preying (mesosaurids, plesiosaurs, mosasauroids, crocodiles)
or browsing (sirenians, hippos) underwater in order to counter
buoyancy. I can hardly imagine a large bipedal animal with an erect
gait such (as a spinosaurid) trying to submerse itself.

Has anyone ever thought about the utility of having a large "sail" in
this case ? As all dinosaurs, spinosaurids needed to maintain a
relatively high body temperature, but they would soon lose heat if
they stay for long in water (even if their large size would limit heat
losses). Just try to imagine (and to not laugh): a *Spinosaurus* is
staying still in a big river, but you can see only its dorsal "sail"
and maybe the tip of its snout (if you are attentive) over the
surface, so that it can get heated by sunlight ! Pretty silly, but
pretty funny explanation isn't it ? :-)

2010/2/6 Augusto Haro <augustoharo@gmail.com>:
> This abstract generates many questions (to me, at least, with certain
> ignorance):
> Does the observed isotopic composition mean that the animal was most
> of its time within a water body as a crocodile, hyppopotamus or
> freshwater turtle?
> Or just that it ate things living in the water body like a heron?
> Do you need a very specialized postcranium to live most of your time
> in the water like a hyppopotamus or crocodile?
> Does the hyppopotamus show many functional differences in its
> locomotor apparatus compared with other large terrestrial ungulates?
> Is there any evidence of greater "bone density" (which may mean, a
> thicker cortex) in the bones of spinosaurids when compared to other
> theropods, or even supposedly terrestrial dinosaurs?
> I do not see a cursorial-looking animal going so bad in the water.
> After all, primarily cursorial dogs dig and primarily cursorial cats
> can climb. Hyppos also seem to have mostly cursorial limbs (in the
> sense of being digitigrade, fore-and aft limited). Many cursorial
> animals can swim more or less well... If its neck moved fast enough to
> catch something, it seems it may not have great trouble...
Jocelyn Falconnet