Taphonomy Tidbits

The following information was derived from Evanoff & Carpenter, 1998

Taphonomy is the study of how an organism becomes part of the fossil record. Paleontologists that study taphonomy might ask how and where an animal lived, how it died, and then what happened to the animal's body after it dies, but before it became part of the rock record. The primary motivation behind the study of taphonomy is to better understand biases present in the fossil record. For example, if a fossil assemblage contains more of one type of fossil than another, one can either infer that that organism was present in greater numbers, or that its remains are more resistant to decomposition.

Sedimentology of the Quarry

To fully understand the taphonomy of the Marsh-Felch Quarry we must begin with an understanding of the depositional environment in which the dinosaurs were buried long before they were ever found in by Marshall Felch.

Evanoff and Carpenter, 1998 deciphered the sedimentology of the Marsh-Felch Quarry primarily from the Marsh-Felch letters because most of the material has been removed from the quarry what is left in the quarry has been covered by a landslide. Fossils of the Marsh-Felch Quarry are found primarily within two distinct sand bodies as reported by Felch in a letter to Marsh (Felch to Marsh, February 11, 1886). The sand bodies were deposited by an ancient river. These two sand bodies are separated by a muddy layer that represents deeper and quieter depositional conditions, or a hiatus in stream flow. The skeletons accumulated in this muddy layer and were later buried by sands when stream flow resumed. Early on, Felch recognized that the bones were laid down in a fluvial deposit and suggested to Marsh in a letter (Felch to Marsh, October 1, 1887) that the animals had been trapped in a "mire hole."

Taphonomy

"[A]s we go on east—we have to leave that deep depression which runs diagonally...and in which all of our best specimens have came from—and in this ground the bones though plenty in places are badly broken and worn—the strata in which they lay is thin—full of rocks and pebbles...and the whole appearance goes to show—these were out of the mire hole—where so many animals got stuck—and what we have now is but stray and scattered fragments brought in by the wash and drift" (Felch to Marsh, October 1, 1887). Felch's description of broken bones found in a thin layer with pebbles and rocks indicates that the bones were probably broken up by the strong currents in the stream channel rather than by modern weathering or by animals that may have been present at the time of death. Felch also reported that water worn bone was common in the quarry.

How did the dinosaurs die?

The bones found in the Marsh-Felch Quarry represent both attritional and catastrophic mass death accumulations. Attritional bone beds represent normal background death within a community due to old age and predation. Catastrophic bone beds represent the sudden death of numerous individuals over a very brief time span. The lowermost layers of the quarry represent attritional bone accumulation as evidenced by disarticulated, beaten, and weather-worn bones found amongst the pebbles at the base of the quarry. As time continued, possible drought conditions became more severe causing the deaths of several individuals within a short time span probably only months. The evidence for this lies in the wide range of disarticulation of the skeletons found in the quarry, which compares to modern drought victims. Dinosaurs that died early on in the drought are represented by skeletons that are more disarticulated than the skeletons of dinosaurs that died later in the drought.