Giant Marine Fossil in Downtown Fayetteville, AR

Submitted by Deborah Cramer

Giant Marine Fossil in Downtown Fayetteville, AR
There’s More Than Rock Here
Photo © Walter Manger, University of Arkansas

Today, the view from Fayetteville, Arkansas is of the mountains, not the ocean. Some 325 million years ago, Fayetteville was underwater, part of a broad sea that covered large swaths of the United States. Large squid-like cephalopods lived in its waters. When they died, their bodies were buried in the sediment, becoming part of the seafloor. Later, when South America and Africa collided with North America to form the ancient continent Pangaea, that seafloor crumpled to become the Ozark Mountains.

The mountains eroded, and the buried fossils came to the surface. Some are odd. In 1963, college students found a giant cephalopod, Rayonnoceras solidiforme, in Fayetteville. While most are a few feet long, this was a giant; eight feet, the longest of its kind ever documented. That is, until 2003, when another group of fossil hunting students found another Rayonnoceras solidforme in a culvert off the interstate. Hidden almost in plain sight, only an inch down in the soil, the fossil was nearly nine feet long.

Walter Manger, the students’ advisor at the University of Arkansas, calls these animals “pathological giants.” He thinks that most Rayonnoceras solidforme, like squids today, may have reproduced only once – laying eggs when they matured, at three or four feet in length, and then dying. For reasons geologists and paleontologists have yet to uncover, parasites may have rendered the two Fayetteville animals sterile. Failing to reproduce, they grew into giants.

The students were lucky. The fossil, close to the soil surface, might have begun to disintegrate and wash away in the next hard rain.

References and more information

Morgan, K.M., Kee, S. F., and Gillip, J.A. 2003. Pathologic Gigantism in Rayonnoceras Solidiforme Croneis from the Lower Fayetteville Shale (Chesterian-Mississippian), Northwest Arkansas. Geological Society of America Abstracts with Programs, 35:6, p161.

Geology of the Ozarks

Map of ancient sea in Arkansas 325 million ago – Late Mississippian (Carboniferous)

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