PSEUDOPATHOLOGY REVISITED: GEOLOGICAL NOISE VERSUS BIOLOGICAL SIGNAL

A critical issue in paleopathology research is the ability to distinguish abnormal alteration of bone that occurs in vivo (true pathological signal) from non-pathologic post mortem alteration (pseudopathology). This issue is well-documented in the archaeological literature; however, paleopathological studies of pre-Quaternary specimens often confine discussions of pseudopathology to taphonomic bone surface alteration (e.g., bone weathering, bioerosion). Less consideration has been formally given to diagenetic crushing and distortion, beyond basic statements that such features are distinct from, and should not be confused with, pathology.

The implication seems to be that diagenetic shape changes should be relatively obvious to recognize. Although this is sometimes the case, distinction is not always a simple matter, and the potential for diagenetic distortion to complicate morphological interpretation may be expected to increase with geological age. Fossil bones are geological objects modified by often millions of years of non-biological processes. Moreover, because researchers investigating fossil paleopathology may be more biologically trained and less attuned to diagenetic modifications, it is useful to begin more specific documentation and codification of ways to recognize diagenetic pseudopathology. Observation of internal bone structure via histologic sampling or CT scanning is useful in distinguishing pathologic from diagenetic signals; however, such methods are either destructive or often cost-prohibitive and may not be appropriate for initial exploration.

In the absence of external reactive bone growth and/or resorption cavities, the potential for diagenetic rather than pathologic origin of unusual morphologies should always be considered. Context of the bones in the sedimentary deposit provides invaluable clues to diagenetic origins of morphological modifications. Quarry maps, recorded orientations of specimens within strata, data on geological evidence of distortion in host sediments, and any patterns of shape change within different parts of the same element and/or across multiple elements recovered from the same locality provide essential information to aid in assessing whether an unusual feature on an individual element is likely to be a pseudopathology.