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by S. Christopher Bennett Background: In the Spring of 2002, David Peters informed me by e-mail that he had found various previously undescribed elements (including the sternum) on the holotype of Anurognathus ammoni. At the time, I was working on a new specimen of Anurognathus and was keenly interested in both the holotype specimen and the new one. Peters sent me a small section of a photograph of the holotype of Anurognathus with the "sternum" illustrated by an overlay consisting of an outline with a colored infilling. In a subsequent discussion of his photointerpretations I argued that he was incorrectly interpreting subtle patterns on or in the matrix of the specimen as bones, impressions of bones, or discolorations produced by bones. Subsequently, Peters reported on my talk on the new specimen of Anurognathus at the 2002 Annual Meeting of the Society of Vertebrate Paleontology in a message to the Dinosaur Listservice, and stated that I was mistaken in my interpretation of both the holotype and the new specimen, this even though he had not examined either specimen and I had intensively studied both. I was very irritated by Peters' dismissal of my work, and consequently readers should be cautioned that the following interpretation may be biased. 
Figure 1. Photograph of the holotype of Anurognathus ammoni (upper figure on p. 93 of Wellnhofer's
1991 book The Illustrated Encyclopedia of Pterosaurs). The photograph was 126 by 126 mm when
printed in the book. The red rectangle represents the area considered in this critique and illustrated in Figures 2-15.
The area of the specimen within the red rectangle is approximately 35 by 27 mm. Photointerpretation of Anurognathus: For this critique of Peters' photointerpretation, I will focus on a small region of the holotype of Anurognathus ammoni, specifically the cranial region shown in the red rectangle in Figure 1. I am focussing on only a small section of one specimen because consideration of even a small area takes considerable time and considerable disk space and bandwidth, but I could present similar observations on the entire area of the holotype of Anurognathus or other specimens. I chose the cranial region of Anurognathus because it seems to be representative of Peters' photointerpretations, and because I have recently spent a lot of time studying the cranial regions of the holotype and the second specimen. Various different views of Peters' interpretation of the cranial region of Anurognathus are shown below.  
Figure 2. Detail of David Peters' image of the cranial region of Anurognathus ammoni with structures
illustrated by outlines infilled with color and labeled, all on a white background. Note that this and
subsequent figures are at 600 dpi. I could not find a key to Peters' labels, but I think they are as follows:
AR - articular, F - frontal, L - lacrymal, LJ - left jugal, LM - left maxilla, N - nasal, PL - palatine, PM -
premaxilla, PMasp - ascending process of premaxillae, PO - postorbital, PT - pterygoid, Q - quadrate,
RJ - right jugal, RM - right maxilla, SCL - sclerotic ring, and SQ - squamosal.  
Figure 3. Detail of David Peters' image of the cranial region of Anurognathus ammoni showing the pattern
of lines that he has drawn outlining "elements" he has identified on a white background.  
Figure 4. Detail of David Peters' image of the cranial region of Anurognathus ammoni showing the pattern
of lines that he has drawn outlining "elements" he has identified superimposed on his base photograph.  
Figure 5. Detail of David Peters' image of the cranial region of Anurognathus ammoni showing only his
base photograph. As far as I know, Peters has not discussed his methodology in detail anywhere; however, he has told me that he uses a MacIntosh computer and Photoshop software. He seems to select a photograph of a specimen, scan it into his computer, use descreen processing, draw lines around and along features he identifies in the photographs, and interpret the pattern of lines as skeletal elements. I compared his base photograph of Anurognathus with Wellnhofer's photo (Figure 1) and they are clearly the same. While Wellnhofer's photo shows the entire specimen well, it has low angle lighting that produced a great many shadows, which reveal the irregular texture of the matrix, but often obscure other details of the specimen. Wellnhofer's figure was printed using screen printing and the coarse pattern of the screen and the strongly shadowed areas are readily apparent in Figures 6 and 7.  
Figure 6. Detail of the original image from Peter Wellnhofer's The Illustrated Encyclopedia of Pterosaurs
showing the cranial region of Anurognathus ammoni. I scanned this image at 600 dpi using an Acer Acerscan
Prisa 610S scanner and Ulead Photo Plus 4.0 software, and did not use any descreen processing. Note the
prominent screen pattern. When processed using the maximum descreen setting the resultant image
approximated Peters' base image. 
Figure 7. Comparison of the left side of the image in Figure 6 (left) with a considerably lightened version
(right) demonstrates that the lack of detail in the shadows is present in the original photo. Below are comparisons of the left and right sides of Peters' base image (Figures 8 and 12) with Wellnhofer's original image, which show the smoothing and blurring effect of the descreen processing on Peters' base image. Figures 9-11 and 13-15 then compare the left and right sides of Peters' interpretation with Wellnhofer's original image.
Figure 8. Comparison of the left side of Peters' base image (left) with the original image from Wellnhofer (right).
Figure 9. Comparison of left side of Peters' interpretation (left) with the original image from Wellnhofer (right).
Figure 10. Comparison of left side of Peters' pattern of lines that he has drawn outlining "elements" he has
Figure 11. Comparison of left side of Peters' pattern of lines on a white background (left) with the original image
from Wellnhofer (right). Note the amazing amount of detail that Peters was able to "extract" from the deep shadows.
He interpreted that region as containing many small elements of the sclerotic ring plus the lacrymal, quadrate, and left
jugal. Unfortunately my examinations of the holotype specimen convinced me that there is no bone nor any trace of
bone in that area.
Figure 12. Comparison of right side of Peters' base image (left) with the original image from Wellnhofer (right).
Figure 13. Comparison of right side of Peters' interpretation (left) with the original image from Wellnhofer (right).
Figure 14. Comparison of right side of Peters' pattern of lines that he has drawn outlining "elements" he has
identified superimposed on his base image (left) with the original image from Wellnhofer (right). Figure 15. Comparison of right side of Peters' pattern of lines on a white background (left) with the original image from Wellnhofer (right). Note the large number of lines drawn in the regions identified as the frontal (top) and also the shadowed area that Peters interpreted as the premaxilla (lower left). Again, my examinations of the holotype specimen convinced me that there is no bone or actual impression in those areas. My Examinations: Based on thorough microscopic examination of the holotype skull I identified those bones or impressions of bone illustrated in the camera lucida drawing (Figure 16). I was unable to find any other features that seemed to be anything other than normal irregularities of the limestone matrix in the areas where Peters identified sclerotic plates, the anterior part of the right and left maxillae, and the premaxillae. Similarly, neither Döderlein nor Wellnhofer, who must also have carefully examined the specimen before preparing their respective descriptions of the specimen, were able to find any evidence of bones or impressions in those regions. 
Figure 16. Camera lucida drawing of the cranial region of the holotype of Anurognathus drawn by Chris Bennett,
May 2002. Discussion and Conclusions: Comparison of David Peters' interpretation of the holotype of Anurognathus ammoni with my observations of the same specimen indicates that Peters is very often misidentifying irregularities in the fractured surface of the limestone as bone or traces of bone. In addition, the comparison also shows that Peters did not correctly identify bone fragments or clear impressions of bone that are readily apparent when examining the specimen under the microscope. For example, Peters did not identify either of the two straight fragments of bone that are preserved roughly parallel to one another in the middle of the camera lucida drawing and just above the shaft of the wing phalanx. He also did not correctly identify the impressions of the ascending process of the premaxillae (=the ascending process of the right maxilla of Peters) or the symmetrical impressions adjacent to it. Note that I have not concerned myself at all with Peters' identifications of bones as particular elements, I have only been concerned with the question of whether he could correctly identify the presence or absence of bone or traces of bone. Given the failure to identify actual fragments of bone on the specimen plus the misidentification of surface irregularities as bone or traces of bone, I must conclude that David Peters' photointerpretation methodology is seriously flawed and all his interpretations of pterosaur osteology are suspect. Furthermore, I must also conclude that his frequent unsupported pronouncements on pterosaur morphology and relationships are also suspect. |