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by Wayne Itano
In August 1991, I attended Dr. Richard Stucky's two week field course in paleontological methods [Note added: Dr. Stucky is currently Chief Curator of the Collections and Research Division of the Denver Museum of Natural History]. We were searching for Eocene mammal fossils in the Sand Wash Basin of northwestern Colorado., but about all I could find were uninteresting fragments of mammal bones and turtle shells. After the first week, I needed to get away for the weekend. Most of the class headed northwest to dig for fossil fish from the Green River Formation, but I headed southeast toward McCoy, Colorado.
McCoy, in Eagle County, is a well-known Middle Pennsylvanian fossil locality, deposited roughly 300 million years ago. Marine invertebrate fossils are abundant and varied there. I like collecting invertebrate fossils, because I find them easier to find than vertebrates, and, within limits, amateurs can legally collect them on public land. I've been to McCoy several times over the last 8 years and have found brachiopods, gastropods, corals, crinoids, echinoids, nautiloids, and other invertebrates.
I spent Saturday looking at three different localities near McCoy. On previous trips, I had just noted roughly the locations where I found fossils. This time I tried to record the stratigraphy and the rock unit from which each specimen came. I found some good specimens, though all of them were familiar to me from McCoy and from Pennsylvanian deposits in Texas.
Then I spotted something unusual poking out of a bank of soft shale. It had beaded, parallel ridges, and my first thought was that it resembled the arms of a crinoid. I carefully dug it out and collected some fragments that had weathered out and rolled down the slope. The pieces fit together to form a thick, tapered rod about 7 inches long. It looked nearly complete; only some of the narrow end was missing. Most of the surface was covered with rows of small bumps. I had no idea what it was. The outside shape was somewhat like an orthocone (straight) nautiloid, but there was no sign of the separate internal chambers that such a fossil should show.
I returned to the Sand Wash Basin on Sunday and showed it to Dr. Stucky. He said that it was a fin spine from a fish. Although Paleozoic fish are not his main interests, he gave me the names of some specialists who might be able to help identify the specimen.
The day after I returned to Boulder, I was browsing through a used book store and spotted The Paleozoic Fishes of North America, written by John Newberry in 1889. In it, I found pictures of several spines that resembled mine. All of them belonged to the genus Ctenacanthus (pronounced with a silent c: tee-nuh-can-thus), a kind of shark. I bought the book.
I wrote to Dr. Hans-Peter Schultze at the University of Kansas and sent a photograph of the spine. He wrote back that my specimen was indeed Ctenacanthus and referred me to an article by Dr. John Maisey of the American Museum of Natural History.
Maisey's article was just what I needed to catch up with what had been learned about Ctenacanthus in the century since Newberry's book was published. Fossil sharks are particularly difficult to identify, since their skeletons are rarely preserved, and we usually find only scraps like teeth and fin spines. Having nothing else to go on, early paleontologists sometimes named several different species, each based on differently shaped teeth from the same shark! Most species of Ctenacanthus are identified on the basis of fin spines. A few articulated specimens, showing more complete remains, have been found. During the 1980's, Maisey wrote three articles "straightening out" the genus Ctenacanthus. He found that many of the species previously included in Ctenacanthus were different enough to be other genera. He also concluded that eight previously described species were indistinguishable from the species Ctenacanthus major.
I took the spine to the September WIPS meeting. To my surprise, some other members brought similar, but less well preserved, spine fragments from McCoy. I also found that Ctenacanthus spines from McCoy had been reported previously, in a University of Colorado master's thesis by Dr. Calvin Stevens and in a preliminary report by Dr. Martin Lockley.
I wrote to Dr. Maisey, described my find, and said that I thought it was Ctenacanthus or Bythiacanthus, a related genus. I offered to donate it, if he was interested. He wrote back that he would gladly accept the donation and could have a cast made for me. I shipped the spine to him, along with photographs and descriptions of the locality where it was found. He quickly sent a reply: "I must thank you for your generous gift to the American Museum, of the fossil shark fin spine from McCoy, Colorado. It is really an excellent specimen and an important find. I must congratulate you on your careful and detailed collecting and recording. The photos, locality information and enclosures are certainly useful, and I applaud you (thanks very much for these!) for being so meticulous!" He said that he thought it was Ctenacanthus and not some other genus. He also noted that it was similar to several described species from the Mississippian Period.
A few days later, I received a form letter from the American Museum, thanking me for my generous donation to the Museum and reminding me that many employers will match donations made by their employees. I soon realized that the letter was referring to a small monetary contribution that I had made to the Museum several months before, and not to the donation of the fossil. The thought of my employer trying to come up with a matching Ctenacanthus spine gave me a laugh!
Finally, in March 1992, 1 received a package from the American Museum. Inside was a very nicely made cast of the spine. It shows the fine details of the surface very well. It should stand up under handling better than the original.
That pretty much wraps up my story. At first, I hoped that I had made a significant discovery. It turned out that similar spines had been found in the McCoy area, but it is still possible that the one I found is the most complete one available for scientific study. (Of course, there may be others in private collections. I'd be interested in seeing other specimens.) Does it correspond to a described species? Probably not, since it is much younger (Middle Pennsylvanian) than the other described species of Ctenacanthus, which are Upper Devonian to Lower Mississippian. [Note added: Other fin spines from the Pennsylvanian and Permian Periods have previously been assigned to Ctenacanthus, but Dr. Maisey didn't consider them to be "true" Ctenacanthus, according to his modified diagnosis.] Will it ever be described as a new species? Probably not, unless more complete remains are found. It is no longer the practice to describe a species from a single spine, and for good reason. Am I glad that I donated it? Absolutely, especially since I was able to find the person best able to evaluate it. Now it is available for anyone to study, and may make a small contribution to science. When we amateurs find something unusual, I think we have a responsibility to find out whether it is of any scientific interest and to consider giving it up so that others can study it.
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