Differential diagnosis of vertebral spinous process deviations in archaeological and modern domestic dogs

Paleopathological study of domestic animal remains can elucidate human-domesticate relationships, when all reasonable differential diagnoses are considered. Deviated spinous processes found on ancient domesticated dog vertebrae have been assumed to result from pack burdens, although consideration of diagnostic alternatives has been unclear. To more thoroughly assess the potential significance of these features, we first generated an extensive differential diagnosis of potential causes. Broad causal categories included: (i) morphological; (ii) infectious; (iii) taphonomic; (iv) life history (in utero to death), with numerous subcategories that sometimes overlap. We then evaluated these possibilities through an observational and radiology study of 15 ancient deliberate domestic dog burials (191 vertebrae) from the midwestern USA, dating between 10,130 and 200 years ago. Archaeological specimens from the UK were included to evaluate for geographic uniqueness of our observations. We characterized deviations of spinous processes of cervical (n = 74), thoracic (n = 51), lumbar (n = 60), and sacral (n = 6) vertebrae. Affected spinous processes were found in 34% of cervical vertebrae, 63% of thoracic vertebrae, 78% of lumbar vertebrae, and 50% of sacral vertebrae. Four types of spinous process deviations were observed: (a) lateral leaning from the base but not otherwise deviated; (b) lateral curving at some point above the base; (c) bowing because of multiple curves; and (d) torsion along the vertical axis. Computed tomography and micro-computed tomography were essential tools for establishing differential diagnoses.