Identification of ecological, locomotor, and morphological indicators of semi-terrestriality in anthropoid primates.

Semi-terrestriality , the utilization of both arboreal and terrestrial environments, is commonly discussed in the primatological literature but inconsistently defined, limiting its study in fossil taxa. This project aims to fill that gap by investigating the ecological, morphological and locomotor variables that characterize semi-terrestrial taxa.

18 semi-terrestrial and 17 arboreal anthropoid taxa were identified from the literature. Ecological data were collected from mammalian demographic and environmental databases; postcranial measurements and behavioral data were collected from the literature. Three stepwise canonical variate analyses (CVA) were run (ecological, locomotor, and morphological) to identify factors that discriminate between semi-terrestrial and arboreal primates.

The ecological CVA retained population size, social group size, and percentage of leaves in the diet as variables. CV1 (55.8%) differentiated semi-terrestrial platyrrhines from arboreal and semi-terrestrial catarrhines. CV2 (26.9%) distinguished semi-terrestrial platyrrhines and catarrhines cluster away from their arboreal counterparts. The behavioral CVA retained bridging, leaping, quadrupedal walking, climbing, scrambling/clambering and bimanual suspension as variables. CV1 (62.3%) separated semi-terrestrial platyrrhines from semi-terrestrial catarrhines, while CV2 (31.5%) distinguished both semi-terrestrial taxa from arboreal taxa. The morphological CVA did not retain any size-corrected variables, with no iteration of relative long bone lengths differentiating between any of the groups.

These results indicate select ecological and locomotor variables can reliably identify semi-terrestrial taxa, helping to improve our understanding of this enigmatic behavior. Future studies should likely include measures of specific bony features to more fully investigate potential morphological indicators of semi-terrestrial behaviors.