Data from: Aerodynamic reconstruction of the primitive fossil bat Onychonycteris finneyi (Mammalia: Chiroptera)

Bats are the only mammals capable of powered flight. One of the oldest
bats known from a complete skeleton is Onychonycteris finneyi from the
Early Eocene (Green River Formation, Wyoming, 52.5 mya). Estimated to
weigh ~40 g, Onychonycteris exhibits the most primitive combination of
characters thus far known for bats. Here we reconstructed the aerofoil of
the two known specimens, calculated basic aerodynamic variables, and
compared them with those of extant bats and gliding mammals.
Onychonycteris appears in the edges of the morphospace for bats,
underscoring the primitive conformation of its flight apparatus. Low
aerodynamic efficiency is inferred for this extinct species as compared to
any extant bat. When we estimated aerofoil variables in a model of
Onychonycteris excluding the handwing, it closely approached the
morphospace of extant gliding mammals. Addition of a handwing to the model
lacking this structure results in a 2.3-fold increase in aspect ratio and
a 28% decrease in wing loading, thus greatly enhancing aerodynamics. In
the context of these models, the rapid evolution of the chiropteran
handwing via genetically-mediated developmental changes appears to have
been a key transformation in the hypothesized transition from gliding to
flapping in early bats.