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Re: dinosaur humps (was Re: A Whole Bunch Of Questions)



Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:

<From the available illustrations, the neural spines of Ouranosaurus and
Spinosaurus look just as rugose in texture as those of Bison or
Gigantocamelus.  Indeed, it would be hard to disprove rugosity in
Spinosaurus, given the state of the material.  One of Bailey's main points
was that humped artiodactyls have transversely narrow neural spines (which
I can confirm), not "at least as mediolaterally broad as they are
craniocaudally long" (pg. 1126), so that is not a valid criticism.>

  In comparison, *Bison* and *Spinosaurus* are not comparable. No extant
ungulate has a thoracic neural spine as narrow as that seen in
*Spinosaurus* or *Ouranosaurus*, though they do near the condition in
*Acrocanthosaurus*. Rather, a few extinct ungulates do bear neural spines
in ther thoracic region that have proportions near to that of
*Ouranosaurus*; they stiull have distal transverse expansions of the
spines and are relatively broader than in *Spinosaurus* whose spines,
contra the above observations at least to this observer, give or take the
spines that are deformed and quite wavy in transverse aspect, are very
smooth, lack lamina except near the base, where there is a basal
craniocaudal expansion that likely braced the strong epaxial muscles that
moved the spine itself. Otherwise, and all ungulates (including several
powerfully spined brontotheres which have the record for spine to centrum
ratio), the neural spines lack distal transverse expansion, bear a single
longitudinal channel on both cranial and caudal margins, and taper or are
semi-circular in profile rather than being rectangular in aspect distally.
*Spinosaurus* is comparable only in the centrum/spine length, whereas
Bailey's conclusions might best be restricted to *Ouranosaurus* in which
the neural spines bear more similarities than does *Spinosaurus*. Mickey
cites rugose texturing, and observes a poor preservation, but this is
wrong: the material was very well preserved, with smooth and perfectly
articulated spines when recovered -- McGraf was a very competant field
worker, and though the material of *Paralititan* is not perfect in
preservation style, this was no meter to the perservation the type of
*Spinosaurus* was in: the plates available from Stromer show no doctoring
-- other material from Baharija show various styles of preservation,
including some as in *Paralititan*, some worse off, some better off, and
the condition of the last matches that of *Spinosaurus*, so I am given to
think this is inadequate a refutation. If there are further similarities,
then I would be willing to hear them.

  As for humped animals, no -- I repeat NO -- animal has a hump which is
correlated to bones. The humps of zebu cattle and camels are above the
bones, and in camels occur caudal to the shoulders. The elongation of the
neural spines between the shoulder blades occurs as a brace to the nuchal
ligaments for supporting a massive head at the end of a short neck lacking
neural spines. This is hardly a problem in theropods or iguanodontians
which have relatively robust cervicals fully capable, via the "S-curve"
design, of supporting a head without neaural spine bracing. The point of
the withers hump in ungulates is entirely unneccessary in theropods at
least, and for obligate bipeds such as the slender-armed *Ouranosaurus*,
would have been pointless given the robust neck and small skull compared
to a relatively short-spined ungulate such as the camel. 

<Bailey specifically argued such neural spines were for the attachment of
"large epaxial ligaments and muscles", so you are not contradicting him
here.>

  Suchg neural spines are for the attachment of the nuchalis ligamentum
series and their positions and size differ given the size and relative
function of the head; in animals that wrestle with their heads and have
short necks, such as bovids, these become _very_ long, and the neccessity
of anchoring occipital muscles and the many dorsal cervical muscles to the
base of the shoulder, including the massive ungulate trapezius and the
coincidental longissimus behind the shoulder (for leverage of the pivot at
the shoulder and leg) would reguire these to be very large; in extant
animals, this condition is seen in bovine bovids, and in extinct forms
best seen in the brototheres, as perhaps most extreme of all ungulates.

  Bailey's flaw is that he fails to correlate the spine height and breadth
at the distal end with a functional relationship to the short neck and
large skull being supported. In the reptiles to which the "hump" theory
was applied, this is hardly a problem, as the neck is far more robust and
the skull hardly as massive.

I had written:

<<A fatty hump has no skeletal analogue and cannot be indicted or
contradicted on osteological material.>>

<And no one's arguing for its presence, so it's useless to mention.>

  Not when someone's arguing for humps in dinosaurs, such as Bailey. The
muscular component of the *Spinosaurus* dorsal series is lost without the
longitudinal lateral ridges marking the boundaries between the vertebral
musculature from vertebra to vertebra (and not the interspinals which are
marked by the longitudinal cranial and caudal channels). The complex of
intervertebrals in *Spinosaurus* appear to have been limited to the
expanded base of the spine. 

<Do all tall-spined artiodactyls?  Bison seems not to have very much
transverse expansion.>

  From what I've seen, *Bison* simply HAS a transverse expansion, I've not
looked at a *Bison* anterior thoracic in person, or seen a reliable photo
of one. In *Bison antuquus*, at least (which has very tall neural spines
in the shoulder and among the tallest of ungulates known), the transverse
expansions are distinct and do not bear the narrower condition in
*Ouranosaurus*, but I could be reading the bones wrong. *Ouranosaurus* has
slight expansions, certainly not to the extreme seen in *Barsboldia*
caudals or stegosaurids, and certainly not to the extreme seen in buffalo.

  http://www.tarpits.org/education/ guide/flora/bison.html offers a link
to *Bison antiquus*, and the expanded distal ends are clear.

  http://lamar.colostate.edu/ ~lctodd/coding.htm offers a link to photos
of the a modern *Bison bison*. Here, at least, a rugose texture as seen in
*Acrocanthosaurus* is missing, whereas the bones preserve similar laminae
on the lateral surfaces of the cranial and caudal margins, also seen in
*Acrocanthosaurus* but absent in *Ouranosaurus* or *Spinosaurus*. The
distal expansion is conspicuous, and from Tacquet's osteology of
*Ouranosaurus* vertebrae, the distal ends are no so nearly as
conspicuously distally expanded, and this expansion is absent in
*Spinosaurus*. In fact, given the anatomy, aside from the lack of a
circular or ovate cross-section, *Spinosaurus* spines resemble those of
purported thermodynamic *Dimetrodon* spines, given their apparent lack of
much muscular support. Bailey would have much better luck, in my opinion,
in moving away from "humps" and sails to muscular support in spines or the
lack thereof. Conclusions further from that would be best. Especially
since humps in mammals tend to be camelid in form in most people's minds,
as in this one's.

<Even when they are not, why is it necessary for the development to be
equal in dinosaurs and mammals?  Sure such expansion increases the area
for epaxial attachment, but organisms are not as well adapted anatomically
as would be possible.> 

  The degree of mammal spine development gives us a resounding correlate
between bone and muscle. To assume otherwise for dinosaurs, so that
simialr muscles would be on the spines without similar anchors to mark
their place, would invariably fall flat in the face of comparative myology
and the evidences given for fossil forms. All for one, as it were, except
when rare taxa depart from the norm. For the most part, in hadrosaurs and
iguanodontids, the neural spines are tall and still have a similar form to
ungulates. Where else to draw the line, when one form departs from this? I
see no reason to give *Spinosaurus* a hump versus a sail.

<So again, you're saying distal transverse expansion is for the attachment
of "large epaxial ligaments and muscles", which is exactly what Bailey
argues.>

  See above. Lacking in *Spinosaurus*.

<Whether it's connected to a spine table or laminae is of no consequence,
as they are functionally analogous.>

  Yup.

<Such vertebrae as found in dicraeosaurids would have undoubtedly made a
hump instead of a sail, given their great transverse diameter.>

  Indeed. In *Dicreaeosaurus*, the cervical neural spines are expanded
distally and laminae continue along the spinal diaphyses tot he distal
end; this condition is lacking in *Amargasaurus* as, as in *Spinosaurus*,
the lamina are basal only on the spines and the spines tape to the ends. 

<At the best, they agree with his conclusions, or state that the
dinosaurian condition was less developed than the mammalian one (but not
demonstrably different).  At the worst, they are inaccurate or
inapplicable to the debate.>

  Except that they do not exist except here. There is one major proponent,
and one major opponent, as far as I can tell. The dinosaurian condition is
in fact similar to ungulates. The problem is in *Spinosaurus*
applicability, since it, of all dinosaurs with tall neural spines, is
distinctly a departure in form.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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

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