A potential pitfall in studies of biological shape: does size matter?

1. The number of published studies using geometric morphometrics (GM) for analysing biological shape has increased steadily since the beginning of the 1990’s, covering multiple research areas such as ecology, evolution, development, taxonomy and palaeontology. Unfortunately, we have observed that many published studies using GM do not evaluate the potential allometric effects of size on shape, which normally require consideration or assessment This might lead to misinterpretations and flawed conclusions in certain cases, especially when size effects explain a large part of the shape variation.
2. We assessed, for the first time and in a systematic manner, how often published studies that have applied GM consider the potential effects of allometry on shape.
3. We reviewed the 300 most recent published papers that used GM for studying biological shape. We also estimated how much of the shape variation was explained by allometric effects in the reviewed papers.
4. More than one third (38%)...