Markings on fossil leaves appear to be the 'death grip' of ants infected by the so-called zombie fungus, Ophiocordyceps. The fungus causes the infected ants to move to a position on nearby vegetation and die immobilized there, such that the sprouting fruiting body of the fungus will more efficiently spread its spores over yet more ants. This grip leaves distinctive markings on the leaves, which were recognized by a group led by David Hughes (disclosure: I have met David and heard him talk about his work).
Having this fossil evidence allows us to be able to give a minimum age for the history of this fungal life-style. Despite advances in the study of molecular evolution, fossil evidence is still the most direct way to pin a date on events in the history of life. Earlier hopes that the rate of changes in nucleotide or amino-acid sequences could provide an objective 'molecular clock' (first proposed in the 1960s by Emile Zuckerkandl and Linus Pauling - yes, that Linus Pauling) turned out to be premature, because rates of molecular evolution are not generally uniform across species and even in single lineages over time, and therefore need to be calibrated, typically against the fossil record.
On the topic of science reporting: The Guardian newspaper article linked above is better than most newspaper science reporting, however, it still illustrates a few sticky points that nag at me when I read about science in the news.
Chief among these is the lack of citations. That is disconcerting, especially to someone in an academic setting where proper attribution is always emphasized. Science reporters are quite uneven in how they cite things: some simply omit any mention of where the research they describe is going to be published (or has been published), some state the journal name and leave it at that, and only in a few cases is a full citation (or in this article: a link to a PubMed record) given. Here, however, note that the PubMed link is to an earlier paper on a related topic, but not about the issue being directly reported. The article says that the scientific report is published in Biology Letters, but a quick search in the journal's website turned up no hits. Hence I can only conclude that it's yet to be published, and the reporter was privy to a prepublication preview.
Unfortunately, this affects blogging, too. I'm happy to highlight interesting papers and newspaper reports on biology, but without having seen the original paper, if new research is being presented, it is hard to assess the quality and reliability of the work, and whether it really is worth being blogged about. Worse yet, the reporter may have distorted the actual conclusions, or misrepresented the facts, ... the list goes on.
So the next time you see a newspaper article reporting new research, do keep an eye out - drop a comment here if you see something noteworthy that shows how caution is necessary.