August 11. Permian fusulinids

Permian fusulinid from Iowa about 12 mm long (Mark Wilson photo)

Fusulinids, one-celled animals that made shells, had proliferated in the Carboniferous and they continued to expand during the Permian. These critters were really large compared to most single-celled organisms, and some Permian types were more than a centimeter long. Their cross-sections reveal complex internal compartments where the animal lived, and some had coiled spiral chambers. Their shells were calcite, not silica like diatoms and radiolarians, and sometimes they were so abundant that they are the principal component of limestones. 

Fusulinids were an order within the phylum of foraminifera, amoeba-like single-celled organisms that made shells with tiny holes in them. Most of them probably lived within the mud on the sea floor, but some probably were floaters. Either way, they had thin filament-like pseudopods that they extended from the shell to catch food. 

Although there are many living kinds of foraminifera, fusulinids were among the many forms of life that became extinct at the end of the Permian in the great mass extinction event then. The had a run of about 190 million years though – pretty successful for a little animal.

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Today’s geological birthday is Robert Thomas Hill, born August 11, 1858, in Nashville, Tennessee. Hill was a pioneer in the study of Texas geology, and he taught some of the first geology courses at the University of Texas.

—Richard I. Gibson

Permian fusulinids 

Photo by Mark Wilson (public domain) Permian fusulinid from Iowa about 12 mm long