98-1 Detecting Environmental Stress in the Fossil Record Through Harris Line Analysis: An Assessment of Columbian Mammoth Remains from Waco Mammoth National Monument

Session: Linking Biodiversity Loss to Environmental Stressors Through Integrated Approaches

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Abstract:

Physiological stress during skeletal development can disrupt longitudinal bone growth. In some species, a dense lens of bone tissue will form in the ribs and limb elements when growth resumes. This feature, called a Harris line, appears in radiographs as a highly-attenuating band parallel to the growth plate cartilage. Because Harris lines are more prevalent in stressed populations than their non-stressed counterparts, Harris line analysis can be used to detect ecological disruptions. Waco Mammoth National Monument (WMNM) is a Late Pleistocene fossil site in central Texas that preserves Columbian mammoth (Mammuthus columbi) assemblages from at least three intervals, the earliest of which occurred ~66 kya. Taphonomic, ichnological, and geochemical data from the site are consistent with recurring episodes of drought, suggesting the potential for mammoth populations exhibiting Harris lines and other pathologies.

 Gross examination of mammoth humeri (N=20), ulnae (N=15), femora (N=20), and tibiae (N=10) from WMNM documented the presence of strongly developed Harris lines in multiple specimens, which were confirmed through plain radiographs (X-ray) and computed tomographs (CT).  These results suggest the WMNM mammoth population may have been stressed by environmental pressures. We also compared mammoth specimens from WMNM to mammoths from two other Pleistocene sites in Texas, Friesenhahn Cave near Boerne and Wright Materials Quarry near Corpus Christi. The Friesenhahn Cave mammoth presented with one partially developed Harris line, and no pathologies were detected in the Wright Materials Quarry mammoth. While this suggests a higher prevalence of Harris lines in mammoths from WMNM, Harris line analysis is best applied to populations, which will require examination of more individuals from Friesenhahn Cave and Wright Materials Quarry.

This study is the first documentation of Harris lines in proboscideans, which widens the phylogenetic distribution of the trait to all placental mammals, assuming that Boreoeutheria is not more closely related to Proboscidea than to Xenarthra. Diagnosis of the pathology in xenarthrans would confirm Harris lines as a characteristic stress response in all placental mammals. Within this framework, populations of placental mammals could serve as archives of (paleo)ecological conditions. Application of this analysis may yield insights into extinction events, such as the end-Pleistocene megafaunal extinction, and may also inform conservation efforts of modern threatened species.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9483

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