The relationships and ecology of Deccanolestes, a eutherian mammal from the Late Cretaceous of India that is known only from isolated dental, mandibular, and postcranial elements, have been a topic of considerable interest and debate. A recent comprehensive phylogenetic analysis has placed this taxon within Adapisoriculidae, a clade of otherwise Paleocene arboreal mammals, but unexpectedly resolved this expanded Adapisoriculidae near the base of the eutherian tree. Deccanolestes has been described as having an arboreal or scansorial lifestyle based on its ankle morphology. Here, we present a geometric morphometric study of the astragalus to test hypotheses pertaining to the ecomorphological affinities of Deccanolestes. Shape analyses were performed on extant eutherians and marsupials displaying a range of different lifestyles, but predominantly sampling arboreal forms, as well as relevant Cretaceous to Eocene taxa. In addition, we constructed a neighbor-joining tree based on the shape variables to identify similarities among taxa in astragalar morphology. Our results show that Cretaceous and Paleocene taxa, including Deccanolestes, cluster most closely and form a separate group distinct from extant mammal clades, including extinct Primates. Strong phylogenetic signal in astragalar morphology among extant taxa, as well as apparent phylogenetic clustering of extant and extinct taxa, complicates a straightforward interpretation of the locomotor ecology of Deccanolestes, but our results suggest that the astragalar morphology of Deccanolestes has no analogue among the sampled living species. However, this morphology appears prevalent among Cretaceous and Paleocene eutherian mammals.