The emergence and diversification of dog morphology

Dogs exhibit an exceptional range of morphological diversity as a result of their long-term association with humans. Attempts to identify when dog morphological variation began to expand have been constrained by the limited number of Pleistocene specimens, the fragmentary nature of remains, and difficulties in distinguishing early dogs from wolves on the basis of skeletal morphology. In this study, we used three-dimensional geometric morphometrics to analyze the size and shape of 643 canid crania spanning the past 50,000 years. Our analyses show that a distinctive dog morphology first appeared at about 11,000 calibrated years before present, and substantial phenotypic diversity already existed in early Holocene dogs. Thus, this variation emerged many millennia before the intense human-mediated selection shaping modern dog breeds beginning in the 19th century.

Modern dogs display highly divergent morphology. The vast majority of this diversity was generated through intensive human selection over only the past 200 to 300 years. Dogs were domesticated at least 10,000 years ago, but we know little about their diversity during most of their time with humans. Evin . looked at more than 640 canid crania over the past 50,000 years (see the Perspective by Fillios) and found that by the beginning of the Holocene, dogs already displayed extensive variation. Although dog crania from the Pleistocene were not distinguishable from wolves, the degree of differentiation seen by the end of the era suggests even earlier human-canid associations. —Sacha Vignieri