Email improvements/suggestions to the mods at hn@ycombinator.com.
I've done so in this case suggesting the subhead, slightly edited, as "Marine worms made at least some trace fossil burrows called Bifungites" (71 characters).
Contrary to popular belief, HN does permit title substitution, though it strongly prefers text from an alternate title or article text. See dang's guidance, e.g.:
