Measurements and the Literature

["Jerry D. Harris" <dinogami@hotmail.com>]

> Chris Brochu wrote:
>
> "The trend I'm seeing is toward morphological cladistic analyses that
> rely on museum collections rather than the (untrustworthy) literature"

...then Max Langer wrote:

> I agree with that, in principle. But something keeps worrying me.
>   If it is accepted a priori that no morphological information can be
> gathered from primary descriptions in the literature, what is the point
> of producing such works at all?

  Well, measurements in the literature are fine _provided_ that the 
specifics of how the measurements were taken is delineated in the text.  For 
example, when one gives a number for tooth height on a theropod tooth, are 
they measuring in a straight line from the tip to the midpoint of the basal 
length?  To the point where the cranial or caudal margin intersects the base 
(or root)?  Is the root included?  Or is the length measured along the 
curvature of the tooth?  Which curvature? Or both, and then averaged?  (Josh 
Smith will note in his dissertation that the broad variety of tooth 
measurement types, and the lack of a standard, across the literature is 
"pathetic.")

  Measuring angles is similar -- it's quite difficult to just plop a 
protractor onto a non-flat bone and measure, say, the angle between the axis 
of the vertebral body and an articular process.  One could take a photograph 
of the bone and measure off of that, but error is introduced by the angle at 
which the photo was taken to the plane of the desired measurement, and if 
one is going to delineate cladistic characters such as "0 = angle < 30 
degrees; 1 = angle > 30 degrees," then those errors could be creating (or 
concealing) signals.

  Or let's take the height of a vertebra.  Many vertebrae have ventral 
margins that are concave (arched) in lateral view.  So, if one places the 
vertebra into a set of calipers, where one end of the caliper is at the top 
of the spinous process, should the other end be at the apex of the arch 
(theoretically in the center of the bottom)?  At one of the protruding ends 
of the arch?  What if the spinous process isn't centered, but angled 
cranially or caudally?  Is a measurement projected from the top of the spine 
to a point centered over the body, or is it a straight line down the angled 
spine to the body?

  At any rate, even if the measurement type is defined, another researcher 
may want a particular measurement not taken in a given publication.  Then, 
yes, that researcher will have to go and see the specimen themselves (or 
give instructions on how to take the desired measurement to someone nearer 
the specimen).  But this brings up another point:  if we should all go see 
specimens first-hand for any analysis, where is the funding for all this 
travel coming from?  I don't think it's financially feasible for every 
paleontologist to bop over to Beijing or fly to Rio to view specimens every 
time -- it was to solve this dilemma that publications came about in the 
first place!

  In the future, then, to alleviate the possibility that measurements are 
untrustworthy, perhaps editors and reviewers of future papers should 
emphasize the need for the methodology of the measurements be placed into 
manuscripts before publication.  (Of course, then we get into manuscript 
length/page cost issues...)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316
Phone: (215) 898-5630
Fax: (215) 898-0964
E-mail: jdharris@sas.upenn.edu
and     dinogami@hotmail.com
http://www.sas.upenn.edu/~jdharris

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