I have invoked sexual selection as initiating our hominid family six million years ago in the last common ancestor with chimpanzees as the evolutionary mechanism that established the fecundity of monogamy. This was the first pre-evolutionary event in the establishment of the innovation of selection inclusion between dominance and submission mentalities that opened the path to the coordination of monogamous groups – then leading to the first tool making industry, the expansion of the brain, and finally to the miracle of the human mind.

When thinking about evolutionary innovations, the granddaddy of them all was winged flight, which opened up a whole new ecology. In a recent Science, 340:690-2, it appears that recent soft tissue fossils found in Lagerstattn, China indicate that sexual selection played a large role in the pre-evolution of flight:

Evolutionary innovation

The fossil snapshots that we do have offer much more insight into the evolution of pinnate (modern) feathers seen in living birds… but bird feathers are known to have diverse functions, for example in flight, display, camouflage, and heat retention. Iridescent feathers, long tail feathers, large color patches and dimorphism are all linked to sexual selection in birds. Recent findings suggest that early pinnate feathers also played a role in sexual selection. Investigation of shape and form  of fossilized melanin-containing organelles (melanosomes) has indicated that the forelimb and hind limb feathers  of one maniraptoran dinosaur were patterned with large conspicuous  patches of white and black spots. Inference of plumage color in the “four-winged” maniraptoran Microraptor yielded evidence of glossy or weakly iridescent feathers. Long tail feathers are known from many species during the transition to powered flight. Finally, evidence of sexual dimorphism in early birds was recently confirmed by recovery of a bone tissue unique to reproductively active female birds in a Corfuciusornis specimen with feathering; specimens with long tail feathers were males and those with short tails, females.

Evidence is thus accruing for the function of early pinnate feathers in sexual selection, but there is little consensus on shifts in feather function associated with the evolution of flight.