Disease in an evolutionary context: a study of stifle joint pathology among extinct and extant canids

To understand disease in evolution, it is fundamental to evaluate whether and/or how disease incidence varies across populations and among taxa in a phylogenetic framework. This study of anterior cruciate ligament damage across extinct and extant canid taxa serves to contextualize the problem in domestic dogs. Exceptional preservation of bones at the La Brea Tar Pits and Museum in Los Angeles, USA, allowed detailed examination of 780 fossil specimens from populations of the dire wolf, gray wolf, coyote, and gray fox. Our data was supplemented by examination of same-species skeletons in other museum collections. Pathology was identified and osteoarthritis of the stifle was scored in adult specimens. Anterior cruciate ligament rupture is an uncommon problem in large and small wild Canidae, both extinct and extant. Some dog breeds of differing body sizes, clustered into three clades, had much greater evidence of ACL injury. The tibial plateau inclination angle is similar among domestic dogs, gray wolves, and coyotes. Thus, quantification of the tibial plateau angle and comparisons among taxa reject its hypothesized relevance as determinants of anterior cruciate ligament pathology among canids. The genetic background of populations with this pathology, on the other hand, may well determine its occurrence.