Physical Geology, 9/e
David McGeary, Emeritus,California State University at Sacramento
Diane H. Carlson, California State University at Sacramento
Three undergraduate students from the University of Arkansas made a world-class discovery this week when they uncovered a 325-million-year-old nautiloid fossil just yards from two of Fayetteville's busiest roads. At exactly eight feet in length, their find represents the longest actinoceratoid nautiloid fossil in the world.
On Jan. 20, while the University community celebrated Martin Luther King Day, freshman geology major Sarah Kee and senior Kevin Morgan set out to hunt for fossils. Their excursion led them to a culvert near Interstate 540, where dime-sized ammonoid fossils were known to be abundant.
"We were actually looking for a three-foot nautiloid that was supposedly located there. Kevin was digging. I wandered a few feet off and started digging for ammonoids, and that's when I noticed the calcite," Kee said. Calling Morgan over, the pair began to dig… and dig and dig and dig. "It just kept going and going, and that's when we called Jonathan because we knew we'd need more help," Kee said.
Junior Jonathan Gillip arrived at the site, and the trio hammered, chiseled and chopped their way through the splintery, black shale for the rest of the afternoon. When the unusual size of the fossil became undeniable, they phoned their advisor, geology professor Walter Manger.
"I was skeptical until I got down there to see it for myself. But these students knew exactly what they had," Manger said. "It may have been luck that brought them to it, but knowledge took over from there. They recognized what they'd found and were very conscientious about the excavation."
Manger's initial skepticism can be understood, considering the fact that only one other comparable nautiloid fossil is known to exist. Not coincidentally, that specimen was also discovered in Fayetteville in 1963 by University of Arkansas students and geology professor Doy Zachry. Measuring seven feet, two inches, the 1963 fossil was believed to be the largest in existence until Monday's discovery.
To read more about the find continue below or log onto the University Relations news release site at http://advancement.uark.edu/news/ and follow the links at the end of this page.
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| These are the three students that found the specimen. From left to right they are: Kevin Morgan, Sarah Kee, and Jonathan Gillip. All three are undergraduates in the Department of Geosciences at the University of Arkansas. They came out on their own to collect this site expecting to find fossil cephalopods, but never anything like the largest nautiloid in the world! It just goes to show you that you never know what you're going to find, particularly in the rich fossiliferous strata in northern Arkansas. |
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| View of the specimen in outcrop prior to its removal. The rock unit is the Fayetteville Shale, which belongs to the Mississippi System, Chesterian Series, and is about 325 million years old on an absolute basis. The shale is black because it was formed under low seafloor oxygen conditions in fairly deep water (hundreds of feet) on the edge of the North American continent. Because of the lack of seafloor oxygen, there were no animals living in the mud that might have destroyed the nautiloid when it fell to the seafloor. |
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| Closer view of the Rayonnoceras solidiforme as it was being excavated. The crushed living chamber is clearly visible at the front of the specimen (bottom of the picture). In nautiloids, the animal only occupied about 1/3 the length of the shell. The remainder of the shell was weighted down with deposits that the animal used to control its buoyancy. That also explains why the posterior of the shell isn't crushed. |
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| A closer view of the living chamber shows that the bottom portion of the shell retains the curvature that probably exists in life, while the top is crushed. This specimen is significantly narrower compared to the one found in 1963, and we think that it may be a female because in modern Nautilus, the females have a narrow aperture and the males have a wide aperture. |
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| Closer view of the end of the specimen shows that about a foot of its length was broken off while it was alive. The 1963 specimen shows the same thing. You might wonder what a nine foot nautiloid would run into, but we believe that this breakage proves that both these giants lived longer than normal. Consequently, this older portion of the shale was attacked by boring organisms, like sponges and endolithic algae, and the "tail" fell off during its life. This would have been a nonlethal break and would only have slightly affected the animal's buoyancy. This is one aspect of the new discover that we will begin looking at immediately. |
Links to additional news stories:
USA Today article on the fossil http://www.usatoday.com/news/science/2003-01-23-fossil_x.htm
CNN.com article http://www.cnn.com/2003/US/South/01/23/arkansas.fossil.ap/index.html
MSNBC.com http://www.msnbc.com/news/863303.asp
MSNBC.com http://www.msnbc.com/local/kpom/m265533.asp
MSNBC.com http://www.msnbc.com/local/kpom/m265830.asp
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