Body mass is a key biological variable, but difficult to assess from fossils.
Various techniques exist for estimating body mass from skeletal parameters,
but few studies have compared outputs from different methods. Here, we
apply several mass estimation methods to an exceptionally complete skeleton
of the dinosaur Stegosaurus. Applying a volumetric convex-hulling
technique to a digital model of Stegosaurus, we estimate a mass of 1560 kg
(95% prediction interval 1082–2256 kg) for this individual. By contrast,
bivariate equations based on limb dimensions predict values between 2355
and 3751 kg and require implausible amounts of soft tissue and/or high
body densities. When corrected for ontogenetic scaling, however, volumetric
and linear equations are brought into close agreement. Our results raise concerns
regarding the application of predictive equations to extinct taxa with
no living analogues in terms of overall morphology and highlight the sensitivity
of bivariate predictive equations to the ontogenetic status of the
specimen. We emphasize the significance of rare, complete fossil skeletons
in validating widely applied mass estimation equations based on incomplete
skeletal material and stress the importance of accurately determining
specimen age prior to further analyses.