No nanodiamonds are found.
I reported last year on the novel theory that a meteorite may have caused megafauna extinction in North America (specially) at the end of Pleistocene. This theory relied heavily on alleged evidence of nanodiamonds (carbon spherules containing lonsdaleite, a carbon crystal likened to diamonds and found only in meteorites).
This evidence seems now to be nowhere. That is at least what Tyrone Daulton of Washington University claims: that it is nothing but graphene (graphite) what has been mistaken for lonsdaleite, an error that had happened before.
Source: Science Daily (no paper linked and too lazy to search it myself).