Using osteological measurements to estimate body length in Amazonian manatees

Abstract

Body length is an important parameter in morphological, ecological and behavioral studies of a species and contributes to the understanding of the body condition of individuals. This parameter is essential for conservation and management strategies by informing studies evaluating growth rates, physical maturity and classification of individuals into age groups, promoting better accuracy for the biological parameters of the species. The aim of this study was to identify predictors of body length for Amazonian manatees (Trichechus inunguis) using metric characters of osteological materials. Eleven linear measurements of skull, jaw, scapulae and humeri were collected from 41 Amazonian manatee skeletons of different age classes (calf, juvenile and adult). Data were analyzed by simple linear regression. The condylobasal length was the best predictor of body length for the species (R = 0.943), however, all bones evaluated showed at least one measurement with the capacity to predict body size (R2 > 0.9). Results of this study are useful for inferring body length of Amazonian manatees using bones deposited in museums and biological collections, expanding the informative potential of these materials.

Advances in the knowledge of the biology and conservation of the Amazonian manatee (Trichechus inunguis)

“…The Amazonian manatee is the smallest living sirenian, reaching up to 2.75 m in length and weighing up to 420 kg (Amaral et al, 2010a). The range of body length and weight at birth was estimated as 85 -105 cm and 10 -18 kg, respectively (Best, 1984;Amaral et al, 2010a) and there are no differences in body size or even in cranial characters between the sexes (Domning & Hayek, 1986;Amaral et al, 2010a;Valdevino, 2016;Barros et al, 2017;Valdevino et al, 2021). Growth curves were estimated for captive (Colares, 2002;Albuquerque Junior, 2003) and freeranging individuals (Vergara- Parente et al, 2010), and the growth rates observed, despite methodological differences among studies, were less than 0.4 cm/year.…”

“…Growth curves were estimated for captive (Colares, 2002;Albuquerque Junior, 2003) and freeranging individuals (Vergara- Parente et al, 2010), and the growth rates observed, despite methodological differences among studies, were less than 0.4 cm/year. An allometric pattern of growth is observed in the skull and other bones (Domning & Hayek, 1986;Valdevino, 2016;Barros et al, 2017;Valdevino et al, 2021). Therefore, osteological measurements can be used on body length estimations for this species (Valdevino et al, 2021).…”

“…An allometric pattern of growth is observed in the skull and other bones (Domning & Hayek, 1986;Valdevino, 2016;Barros et al, 2017;Valdevino et al, 2021). Therefore, osteological measurements can be used on body length estimations for this species (Valdevino et al, 2021). Additionally, Brum (2013) demonstrates the potential use of the flipper radiographic evaluation on age estimation of juvenile and young adult Amazonian manatees.…”