96% of marine animal species became extinct in the permian mass extinction at the end of the paleozoic, 251 million years ago. why does the blue curve show only a 50% drop at that time

The blue curve is for marine creature families. Families regularly contain numerous species, and a family just goes wiped out if each species in the family goes terminated. Along these lines, despite the fact that 96% of marine creature species went terminated, this brought about the entire eradication of just around half of marine creature families.