Placostraca (lit. "plate shells") are a clade of herbivorous Diplostoma.
Description[]
First emerging around 4180ma, Placostracans were the earliest group of large-sized terrestrial herbivores. At the peak of their existence, species measured as long as 2 meters.
The Placostracans are the only clade of Lophostoma not to evolve any reductions to the ancestral shell: in fact, most modern Placostracans have heavier, stronger shells as a means of protection. Their top pair of oral tentacles are used to handle food, while the bottom two pairs are used for mastication.
Decline[]
The emergence of the Megalobrachids resulted in the extinction of many large Placostracan species, with the remaining species evolving into the Euplacostraca branch. The emergence of the steppe went alongside a decrease in global oxygen levels, causing the Placostracans to shrink in maximum body size.
