Research: A Brief History – The Discovery and Publication of Pathologically-Pitted Ankylosaur Fossils

by Lorrie McWhinney and Angela (Angie) Matthias of the Western Interior Paleontological Society (WIPS)

Bottom row from left is Lorrie McWhinney in tank top. Second from left is Dr. Ken Carpenter (dark hair and glasses), our museum curator and trip leader. Second row first from left with dark hair and glasses is Angie Matthias.
Bottom row from left is Lorrie McWhinney in tank top. Second from left is Dr. Ken Carpenter (dark hair and glasses), our museum curator and trip leader. Second row first from left with dark hair and glasses is Angie Matthias.

This study slowly developed and changed over 17 years. The discovery of “Lorrie’s Site” in 1999 was a byproductof prospecting for eggshell material for Darla Zelenitsky, then a PhD student from Canada, who is now an Assistant Professor at the University of Calgary. At that time, Dr. Ken Carpenter (director and curator of paleontology at Utah State University Eastern Prehistoric Museum, in Price, Utah) had two sets of volunteer teams prospect in the Cedar Mountain Formation. My co-author, Angie, and Brenda Johnson went in one direction, while Darla Zelenitsky and I (Lorrie) headed toward an exposed area of the Ruby Ranch member of the Cedar Mountain Formation.  No egg shell, but Darla and I found bone fragments littering the ground. Darla decided to search another area for eggshell while I stayed behind. Since I was prepared to find tiny eggshell fragments, I didn’t bring anything bigger to put larger specimens in for collection. Therefore I selected a few specimens and held them in my hand as I continued prospecting for eggshell material. When both teams returned, Dr. Carpenter asked about our findings. No one had found fossil eggshells. However, since I had collected some of the bone fragments, I handed him my findings. Dr. Carpenter instantly recognized what I had found: ankylosaur armor fossils called osteoderms. He asked me to name the site. I said that the name could be the ‘Lady Luck Site’ – I wanted to credit both Darla and me. Unfortunately, this name was overruled and “Lorrie’s Site” stuck instead.

The preparation process in the lab revealed that numerous ankylosaur armor samples appeared pathological. With the encouragement of Dr. Carpenter, I was given the opportunity to investigate why we were finding “pitting” on the exterior of the bone. I used to work for Kaiser Permanente, and so I had a lot of disease resources available to me. It soon became apparent that more samples were needed for a proper investigation. Each subsequent field season increased the number of pathological specimens. After Angie joined me in this investigation, we looked at other museum collections, interviewed many professionals in different fields of expertise, and reviewed endless amounts of publications. Despite the fact that pitting or cratering on ankylosaur osteoderms has been noted by various authors, our study was the first detailed analysis of such pits based on a large sample size of osteoderms. We ended up examining over 1100 osteoderms that exhibited a peculiar pitting with different shapes and sizes. Data on the pits were collected with digital calipers, thin-section analysis, SEM, and non-destructive X-ray computed tomography. The comparative data on pitting in modern relatives, such as crocodiles, was collected from veterinarians as well as from observations of recently-dead alligators.

Normal Osteoderm
Normal Osteoderm
Osteoderm with Pitting
Osteoderm with pitting

 Some of the ankylosaur osteoderm pits pierced the cortical bone down to the trabecular bone and some did not. Because there is no one-size-fits-all description of this pitting, we implemented the Istanbul Protocol (Appleby et al., 2015) which gave us some leeway when trying to describe and diagnose the cause of this pitting. The Istanbul Protocol is a slightly modified system of describing imprecise characteristics of lesions so that all levels of forensic disciplines can understand, without a doubt, each other’s descriptions locally and across the world. In applying the Istanbul Protocol, we ranked the various potential causes of pitting, with ulcerative dermatitis (seen in modern crocodiles) as the most consistent. Because these are fossil specimens, the direct cause for this pitting remains unknown, but our paleopathological interpretation is that osteodermal pitting commonly seen in ankylosaurs may be a result of secondary infection from insects feeding on blood.


Appleby, J., Thomas, R., Buikstra, J., 2015. Increasing confidence in paleopathological diagnosis–Application of the Istanbul terminological framework. International Journal of  Paleopathology, 8, 19–21.

To learn more:

Matthias, A. E., McWhinney, L. A., & Carpenter, K. (2016) Pathological Pitting in Ankylosaur (Dinosauria) Osteroderms. International Journal of Paleopathology, 13, 82-90.

Read about the discovery of “Lorrie’s Site” in this 2000 Denver Post article.