Biology, programming, linguistics, phylogeny, systematics....
That doesn't really help me, except for ruling out the slightly thicker line being a mass extinction. If the dots are species occurrences then it's either a group with a really good record or just a really big group. The odd thing I've spotted that confuses me is the isolated cluster of points at top right. Whatever that group is seems to have a much poorer record than the left-hand 'branch', but I can't fit anything I know to this!
I guarantee that everyone reading this is familiar with the group in question.
Something to do with hominin evolution?
And the man gets a cigar!