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Re: Brachiosaur flexibility and face-shape (Was: Terra Nova: thoughts)



Oh, come on, now, I know there are some here who could not possibly understand ... but the main functino of the brachiosaurs was to look cute.

Dora

----- Original Message ----- From: "Mike Taylor" <mike@indexdata.com>
To: <david.marjanovic@gmx.at>
Cc: "DML" <dinosaur@usc.edu>
Sent: Wednesday, September 28, 2011 3:37 AM
Subject: Brachiosaur flexibility and face-shape (Was: Terra Nova: thoughts)


On 27 September 2011 22:27, David Marjanovic <david.marjanovic@gmx.at> wrote:
That would be one of the few things that Kent and we WOULD agree on.
Assuming that brachiosaurs drank, they would have needed the ventral
flexibility to get their heads down to ground level.

I assume their shoulder mobility didn't allow the giraffe workaround to this
problem?

Actually, no-one should assume ANYTHING yet about brachiosaur shoulder
mobility.  Although the Giraffatitan paralectotype specimen HMN SII
preserves a consecutive sequence of vertebral centra through the
cervicaldorsol transition (C9-D3), all the neural arches are busted
off, including the zygs, so we can draw absolutely no conclusions
about neck flexibility in that region.  See this helpful composite of
Janensch's (1950) figures on Kent's site:

http://ix.cs.uoregon.edu/~kent/paleontology/sauropods/Brachiosaurus/images/cervicodorsalTransition.png

... and now I realise you were talking about flexibility of the forelimb, right?

That's a strange subject.  So far as I can see (and I am absolutely no
expert on appendicular material), there is nothing unusual about the
forelimbs or shoulder girdles of Giraffatitan.  But the coracoid of
the Brachiosaurus holotype FMNH P25107 has a very strange laterally
deflected glenoid, discussed briefly in Taylor (2009:796, 802):

``One of the most distinctive osteological features of
Brachiosaurus is the strong lateral deflection of the
glenoid surface of its coracoid, which in other
sauropods including Giraffatitan faces directly
posteroventrally. This may indicate that the humeri
were also directed somewhat laterally, again in
contrast to the parasagittally oriented forelimbs of
other sauropods. Janensch restored the skeleton of
Giraffatitan with somewhat sprawling upper arms,
reasoning that "In the forelimb the humerus [...]
displays characters that are similar to the conditions
of the humerus of lacertilians, crocodylians and
Sphenodon, even if pronounced to a lesser degree,
which, however, show that, in the type of motion of
the upper arm, a component of lateral splaying was
included" (Janensch, 1950b:99). Ironically, while it
is now established that sauropods in general held
their limbs vertically, it seems possible that
Giraffatitan's sister taxon Brachiosaurus may have
been the sole exception to this rule. If correct, this
would be surprising: the bending stress on a sprawled
humerus would greatly exceed the compressive stress on
one held vertically (Alexander, 1985:18), and the
proportionally slender humeri of Brachiosaurus would
seem particularly unsuited to such a posture.''

The best illustration of the coracoid in question is on SV-POW!,
thanks to photos provided by Phil Mannion:

http://svpow.wordpress.com/2010/01/25/whats-up-with-the-brachiosaurus-coracoid/

Finally:

On 28 September 2011 04:10, Jura <pristichampsus@yahoo.com> wrote:
Not mentioned was the weird faces on the brachiosaurs. Aside from the nostril position choice, they also had duck faces (wide, flat mouths) and their eyes resulted in the goofiest expressions.

I've not seen Terra Nova, so they may well have badgered up the faces.
But the skull of Giraffatitan IS ugly, and the snout is sort of
flattened.  It's best seen in anterior view, but I can't find a
suitable photo on the Web.  (I have one, which I will post on SV-POW!
at some time, but we have other plans for the next week or two.)  In
the mean time, you can get some idea from anterolateral views, of
which the best are (get ready for a huge shock) at SV-POW! -- a photo,
and a figure from Witmer's fleshy-nostrils paper:

http://svpow.wordpress.com/2008/12/03/shedloads-of-awesome-part-2-mike-and-matts-excellent-adventure/

-- Mike.