These rocks are from the late Jurassic Period, about 100 million years after trilobites kicked the bucket

Nothing I didn't already know lol. The best answer for why Volume 7 is a bit of an outlier is that it was the volume that Alex scored pretty much in its entirety (IIRC the only scenes Jeff scored were Ironwood v Watts and RWBY v Ace Ops) and he's the one that just goes ham with thematic stuff lol