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Re: Drawing Mamenchisaurus youngi...

David Marjanovic (david.marjanovic@gmx.at) wrote:

<In principle I agree, but exact lateral views have the great advantage of
making things like total length or presacral length measurable. Without that,
over 2/5 of my M.Sc. thesis would have been impossible.>

  One of my first pieces of advice to those attempting to verbially describe
bones is that they need to perfect their ability to describe them visually.
They will need to actually visualize them in their minds in three-dimensions.
This is actually rather difficult for the most of the people I've talked to.
Artists for the most part are visual, rather than mechanical, thinkers, and
find it easy to conceptualize, and even motivate, images in their head using
imagination. It often works wonderfully.

  The problem with anatomical referents is that they require bases of
comparison, and among animals with coracoids, there are very few. You have the
veterinarian handbook, the reptilian sources, the avian handbook, and the human
anatomical handbook. Some of these groups have no effective coracoid, and
others have a highly everted or modified coracoid that make them difficult to
visualize with novel groups. Furthermore, among reptiles, there is no concise
anatomical reference, something which Mike Taylor encountered and which Tom
Holtz referred to in his reply. One must pick and choose. Descriptively,
however, there is some need for a concise and repeatable method that can be
exchanged with other studies, and in that sense, among different animals of the
same group that will change the orienations and/or positions of the key
features, that makes comparisons VERY difficult without a singular frame of
reference. To which I argue, one can be inventive.

  So, to combine these two tangents, let's conceptualize the coracoid in a
plane. To understand it's relationship with a scapula, one will have to depend
the bone below and into the plane of view, and this is no longer an ideal
descriptive reference of study. Such as, what is the anteroposterior length of
the coracoid? Is it the same as distance between the point of the coracoid that
is most medial to the point that contacts the scapula? Or is the length in
lateral aspect of the animal in life position from anterior to posterior? Does
it end at the dorsal corner or at the glenoid, especially if in life-position
the glenoid is the posterior-most extent of the bone? The orientation of the
bone is important for many anatomical referents, including muscle moment arms,
aspects of fossae or ridges, eversion or lack thereof of the glenoid fossa,
posterior/caudal-most extent of the bone, etc, which effects ratios of the
bone-to-bone, which refers also thereupon to the muscle effects, which can be
valid characters. Mental rotation of a bone is probably a skill with which an
anatomist should develop a definate lot of skill in, as it will allow them to
generate perspectives and even analyse them when critiquing their's and others'
perspectives on the same topic.


Jaime A. Headden

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

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