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Measurements and the Literature



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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