Calcar

Calcar (femorale) also refers to the dense, vertically oriented bone present in the posteromedial region of the femoral shaft inferior to the lesser trochanter.

It is unclear who first coined the word "calcar" to apply to bat anatomy; records of its usage date to Joel Asaph Allen in 1893.

In the hairy-legged vampire bat, the calcar has a unique, finger-like form that extends approximately 3 mm (0.12 in) beyond the edge of the uropatagium.

The gastrocnemius muscle aids in flexion of the foot, working in conjunction with m. depressor ossis styliformis to spread the uropatagium.

[6] The calcar can assist the uropatagium in forming a basket or pouch to help catch and hold insects captured in flight.

[5] The oldest known ancestor to present day bats, Icaronycteris index, apparently did not have a calcar or spur as evidenced by fossil remains.

[8] Some authors have treated the calcar as a synapomorphy, or a unique trait shared by all bats, derived from a common ancestor.

[6][5] In a paper published in 1998, Schutt and Simmons advocated for different names for this structure for the two suborders, with the Yangochiroptera (microbats) retaining "calcar" and the Yinpterochiroptera (megabats) using "uropatagial spur."