The Piaui Formation at 4 localities in eastern and western Parnaiba Basin contains a varied microfauna which includes: arenaceous and calcareous foraminifers, conodonts, bryozoans, ostracods, crinoid columnals, holothurian sclerites, echinoid spines, microgastropods, microbivalves, scolecodonts, sponge spicules, fish plates, teeth, otholits and bone fragments and plant remains. The foraminifers include about 25 different species, i.a.: Tolypammina sp. cf. T. gersterensis, .Ammovertella inclusa, Sorosphaera? cooperensis, Hyperammina sp. cf. H. sappintonensis, H. sp. cf. H. rockfordensis, Orthovertella? sp., Globivalvulina bulloides and Calcitornella sp. A and B. Conodonts present in the fauna are: Cavusgnathus lautus, Cavusgnathus gigantus, Cavusgnathus sp., Idiognathodus magnificus, Idiognathodus delicatus, Ozarkodina delicatula, Gnathodus bassleri and fragments probably of Euprioniodina. The microfauna, particulary the conodonts, indicate an early-middle Pennsylvanian age the Piaui" Formation at the localities examined.
