The Saccopastoris fish is an extinct jawless fish that lived during the Ordovician period, about 460 million years ago. It is mainly known from fossil discoveries in South America, particularly in Bolivia and Argentina. Saccopastoris is one of the earliest vertebrates. It had a unique, flattened, tadpole-like body and a head shield made of bony plates, which provided protection and may have aided in hydrodynamics. Unlike modern fish, it lacked a jawbone and had a mouth adapted for filter-feeding or