Another idea: maybe 3:7 is species count pre, and 7:5 is modern, but 7:5 is not B-rich — unless typo and it’s 5:7 or 7:3. - AMAZONAWS

Another Idea: Could the Rise in Species Ratios from 3:7 to 7:5 Signal a Post-Biotic Shift?
By [Your SEO Nom de Plume], ecology, biodiversity, and evolutionary trends analyst