Nemicolopterus - perhaps the smallest of the pterasaurs
When: Early Cretaceous (~120 million years ago)
What: Nemicolopterus is a pterosaur. It is the smallest one known, its wing span was just 10 inches (25 centimeters) from tip to tip. It was well adapted for roosting in trees with its highly curved toes and sharp claws and is thought to have eaten insects. Nemicolopterus was one of the few pterosaurs to live far inland, most of the group were fish eaters living near or on coasts. The validity of Nemicolopterus is debated; there are strong arguments in favor of it actually being a juvenile Sinopterus. The single specimen of this proposed minute pterosaur has a very large skull for its size and has a simular level of bone fusion as other known hatchling pterosaurs - it is thought the young could fly at a very young age. Sinopterus has a wingspan of 4 feet (~1.2 meters), which is on the small end for pterosaurs. (In the example images for today, the two on the right are of Sinopterus.)
Pterosaurs are archosaurs, members of the group that also includes crocodiles and dinosaurs. Within Archosauria they are more closely related to dinosaurs than to crocodiles. This clade is the first vertebrate lineage to have evolved powered flight, already flying by the late Triassic (~220 million years ago). The pterosaur wing was primarily supported by a hyper-elongated 4th digit, leaving digits I-III free in most taxa. This makes pterosaurs the only flying vertebrate group to have retained free digits, as both birds and bats lost the full use of their fingers in the evolution of their wing mechanisms. Pterosaurs went extinct at the end of the Cretaceous period (~65 million years ago).