Abstract

Stem  mammaliaforms are Mesozoic forerunners to mammals, and they offer  critical evidence for the anatomical evolution and ecological  diversification during the earliest mammalian history. Two new  eleutherodonts from the Late Jurassic period have skin membranes and  skeletal features that are adapted for gliding. Characteristics of their  digits provide evidence of roosting behaviour, as in dermopterans and  bats, and their feet have a calcaneal calcar to support the uropagatium  as in bats. The new volant taxa are phylogenetically nested with  arboreal eleutherodonts. Together, they show an evolutionary  experimentation similar to the iterative evolutions of gliders within  arboreal groups of marsupial and placental mammals. However, gliding  eleutherodonts possess rigid interclavicle–clavicle structures,  convergent to the avian furculum, and they retain shoulder girdle  plesiomorphies of mammaliaforms and monotremes. Forelimb mobility  required by gliding occurs at the acromion–clavicle and glenohumeral  joints, is different from and convergent to the shoulder mobility at the  pivotal clavicle–sternal joint in marsupial and placental gliders.

Nature  volume 548, pages 291–296 (2017)