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Footloose: Articular surface morphology and joint movement potential in the ankles of lorisids and cheirogaleids
Author(s) -
Yapuncich Gabriel S.,
Granatosky Michael C.
Publication year - 2021
Publication title -
american journal of physical anthropology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.146
H-Index - 119
eISSN - 1096-8644
pISSN - 0002-9483
DOI - 10.1002/ajpa.24298
Subject(s) - joint (building) , subtalar joint , morphology (biology) , articular surface , anatomy , surface (topology) , geology , biology , geometry , ankle , mathematics , paleontology , structural engineering , engineering
Objectives The competing functional demands of diarthrodial joints, permitting mobility while retaining enough stability to transmit forces across the joint, have been linked with the shape and size of the joint's articular surfaces. A clear understanding of the relationship between joint morphology and joint movement potential is important for reconstructing locomotor behaviors in fossil taxa. Methods In a sample of matched tali and calcanei of lorisids ( n = 28) and cheirogaleids ( n = 38), we quantify the surface areas of the talar and calcaneal ectal (=posterior talocalcaneal) articular surfaces and model the principal curvatures of these surfaces with quadric formulas. These two taxonomic groups have similar body masses, but differ substantially in positional behavior, so that differences in joint surface morphology should reflect adaptive demands of their locomotor behavior. Results Compared with cheirogaleids, lorisids exhibit: (a) a significantly greater area difference between their paired joint surfaces; and (b) a more pronounced saddle shape for the talar ectal facet. Conclusion The increased subtalar joint mobility observed in lorisids may be achieved by increasing the amount of sliding and rolling that can occur at the subtalar joint. The subtalar joint morphology observed in two fossil euarchontans, the plesiadapiforms Purgatorius sp. and Plesiadapis cookei , compares favorably with the morphology observed among lorisids, potentially suggesting antipronograde postures within these extinct taxa.