FORT WAYNE, Ind.—Fossils constitute some of the best evidence of past life and environments, but do fossils always faithfully record that life? A study based on research generated by a collaborative team of amateur paleontologists in the Cincinnati area, Indiana University–Purdue University Fort Wayne (IPFW) faculty from the Departments of Biology and Geosciences, and geosciences undergraduate students that has been published in the scientific journal PALAIOS explores this question.
Associate Professor Ben Dattilo (geosciences) headed a team of undergraduate researchers with scientist colleagues from several other institutions who were following up on observations made by amateur paleontologist Bill Heimbrock. This research has challenged both the notion that the Cambrian-era small shelly faunas were unique in their preservation, and that small phosphatic fossils occurred in low-oxygen conditions. The research is published in a paper in the paleontological journal PALAIOS, and is summarized in this video.
For the group, the journal article is the first result of years of lab and field research as well as several conference abstracts and presentations. IPFW is largely an undergraduate institution, and Dattilo incorporates cutting-edge research into his teaching. This effort is currently supported by a generous grant from the American Chemical Society, which allows students to work on research projects and present them at scientific meetings. IPFW undergraduate students have enjoyed being a part of the process and working with Dattilo in his geology lab.
Jessie Reeder, one of Dattilo’s student research students, was honored to be included as a contributing author. “This has been an incredible experience working with Dr. Dattilo,” says Reeder, who is interested in a potential career in environmental geology. Reeder logged many hours of research in the lab along with her student colleagues. “We examined the fossils in their host rock and then separated them from the rock using acid. By studying hundreds of samples, we discovered that many of these mold fossils are incomplete in that they record small parts of larger, normal-sized animals, or juveniles, along with smaller species. This finding confirms that the small size of these fossil results from biased preservation, not unusual ecological conditions.”
The study focuses on sedimentary phosphate, which illustrates the problem of biased preservation. Phosphate is a critical resource mined from sediments deposited by ancient continental seas. The origin of phosphate deposited so far from the deep oceans is not well understood. One type of these deposits consists of poppy-seed-sized phosphatic “micro-mold” fossils, mineral fillings of shells. Some of the earliest shelled fossils, from the Early Cambrian time period (about 540 million years ago) are preserved this way. This critical “small shelly fauna” includes snails and a variety of mollusk-like creatures.
Scientists have widely presumed that this small shelly fauna occurred only for that brief “window” of time in earth’s history. Although similar small phosphatic fossil molds are known from younger deposits, these later occurrences have not been well studied, nor had the connection been made between later phosphatic fossils and the more famous small shellies of the Cambrian. Furthermore, these later small fossils have generally been thought to result from growth stunting in oxygen-stressed environments. This in turn has been used as one line of evidence that there were periods in Earth's history when the oceans were oxygen starved.
Then an amateur fossil collector noticed something very odd among some 450 million-year-old fossils from the Ordovician time period. He collected small phosphatic fossils, known locally as the “Cyclora Fauna,” in Florence, Ky.; a tiny comb-like fossil that he found could not match any known creature. Bill Heimbrock, a member of the Cincinnati Dry Dredgers fossil club, worked on the problem for years, and was finally able to match these fossils to small crevices in the hinge of common, normal-sized fossil clams found at other localities. The rest of these large clams were just not preserved. Maybe these small fossils did not represent whole seafloors covered with stunted animals; instead, the small fossil size might have resulted from a bias in preservation.
"For nearly 30 years the amateur paleontologists of the Cincinnati Dry Dredgers have helped me locate and interpret Ordovician fossils in the Cincinnati region,” said Dattilo. “When Bill showed me what he had discovered, I knew he was on to something.”
Heimbrock added, “I’ve spent much the last 20 years identifying odd-looking partial phosphatic molds of full-size clams. It’s no wonder this “Cyclora” hash was thought to be a dwarfed community. Partial phosphatic molds are very hard to identify as coming from normal sized fauna.”
"With Bill’s discovery in mind, we decided to take a closer look at the late Ordovician deposits of the Cincinnati area where tiny phosphatic snails and clams are common in some layers," Dattilo explained. “In addition to the clams, we found evidence that snails, trilobites, and crinoids were all preserved partially, and that preservation was biased toward very small animals, or smaller parts of larger animals. Given this bias, sweeping conclusions cannot be based on the simple occurrence of tiny fossils.”
Coauthor Winfried Peters, an associate professor of biology at IPFW who studies modern snails, observed, “Our findings fit with that we know of the modern world, where shelled mollusks are rare in low oxygen environments. Their presence in the ancient sea does not indicate unusual oceanic conditions.”
“The issue of the diminutive Cyclora fauna has been plaguing Cincinnatian researchers and amateur collectors for years,” noted Jack Kallmeyer, an amateur paleontologist and coauthor. “Always presumed to be molds of tiny mollusks, they were dismissed as less important than trilobites or echinoderms—the more glamorous Cincinnatian fossils. The paper is an example of collaboration between professional and amateur paleontologists all working toward a common goal.”
The paper is summarized in this video.
"Giants Among Micromorphs: Were Cincinnatian (Ordovician, Katian) Small Shelly Phosphatic Faunas Dwarfed?" is the cover article of the March issue of the journal PALAIOS, volume 31, no. 3, p. 55–70. Authors include: IPFW professors Benjamin F. Dattilo, associate professor of geology; Winfried S. Peters, associate professor of biology; Anne Argast, professor of geology; and IPFW senior geology major Jessie Reeder. Additional article authors from other institutions include: Rebecca L. Freeman of the University of Kentucky; William P. Heimbrock and Jack Kallmeyer of the Cincinnati Dry Dredgers; Bradley Deline of the University of West Georgia; and Anthony J. Martin of Emory University.
Students currently working on this research project include Kenneth Ray, Tessa Aby, Mason Frauhiger, Amanda Straw, Michael Stoller, Gretchen Luchauer, Jessie Reeder, and Emma Steele.
Student presentations on related topics highlight research in progress, including an analysis of similarly aged small shelly fossils from Graf, Iowa, and a study of the relationship between depositional rate and the accumulation of phosphate in limestones.
For more information, contact Dattilo at 260-481-6250 or firstname.lastname@example.org.