Body mass estimation in armoured mammals: cautions and encouragements for the use of parameters from the appendicular skeleton

This study explores the relationship between body mass and femoral construc tion in armoured (dasypodids and manids) and unarmoured (caviomorph rodents ) mammals.:Predictive equations based on diaphyseal cross-sectional paramet ers provided the most accurate estimates of body mass in caviomorph rodents and dasypodids. When these equations are applied to the estimation of body mass in manids, relatively low predictive errors (<20%) are found only whe n caviomorph equations derived with diaphyseal cross-sectional area or mome nts of area are used. Dasypodid equations generally yield less accurate est imates for manids, so that armouring of the integument alone poorly discrim inates femoral types. Other factors with potential to differentially impact femoral construction are also considered: although locomotor speed strongl y influences mass-structure relationships within caviomorph rodents, the co nfounding influence of locomotor posture, fossoriality, and arboreality ren der these relationships less predictable across all three groups considered here. Limb structure and, hence, scaling patterns of each phylogenetic gro up are influenced by a unique mosaic of factors that is difficult to summar ize quantitatively. The results of the study provide cautions as well as en couragements for the estimation of body mass for fossil species that have n o adaptively similar living relatives.