The science of Ichnology

Ichnology takes a step forward
Ichnology takes a step forwardCourtesy Mark Ryan
There have been a couple of recent reports about new prehistoric tracks being discovered. The first was the report from Montana of what could be a rare footprint Tyrannosaurus rex. A second discovery involves some 315 million year-old reptile tracks found

recently in New Brunswick in Canada,

The two discoveries are the latest in the science of Ichnology, a specialized branch of paleontology that studies the trace fossils of prehistoric creatures. Trace fossils can be anything that the behavior of an ancient creature has left in the fossil record, such as footprints, borings, burrows, eggs, coprolites etc., anything besides its dead remains. Gene made a recent post about burrowing dinosaurs. The burrow dug by the dinosaur would be classified as a trace fossil. But the bones found at the bottom of the burrow would not.

But since the Object of the Month for November here at the Science Museum of Minnesota is fossil animal tracks, I thought I’d muse a bit about them, specifically dinosaur tracks, a favorite subject of mine.

Dinosaur trackway near Morrison, Colorado
Dinosaur trackway near Morrison, ColoradoCourtesy Mark Ryan
The first recorded dinosaur trackway came to light in 1802 when Pliny Moody, a 14-year-old farm boy, in South Hadley, Massachusetts plowed up a slab of red rock containing several three-toed footprints. Dinosaurs hadn’t even been imagined yet, so the tracks were attributed to giant birds –Noah’s Ravens– as the local doctor called them. Of course, he wasn’t far off since today’s birds are considered descendents of dinosaurs.

Three decades later, Reverend Edward Hitchcock who was president of Amherst College became fascinated with the tracks and started to collect them in earnest. Between 1836 and 1865 he amassed huge numbers of fossil tracks that today make up the world’s largest collection and are held in the newly completed Amherst College Museum of Natural History in Amherst, MA. Hitchcock did extensive study of the trace fossils for the rest of his life, and was the first to classify them into a Linnean system that is still used today. He even made large stony books of the prints by binding together slabs of complementing casts and molds. But in the end, he just couldn’t reconcile his religious beliefs with the evidence the tracks presented and went to his grave still holding on to his belief that they had been made by giant birds.

In 1858, the world’s first nearly complete dinosaur skeleton (Hadrosaurus foulkii) was discovered on John Hopkins’ farm in Haddonfield, NJ and put on public display at the Academy of Natural Sciences in Philadelphia. It was the start of the public’s fascination with dinosaurs that continues to this day. Unfortunately, as more and more dinosaur bones were found, the interest in their tracks diminished.

But in the past two decades new interest in fossil footprints has flared up as scientists begin to realize their value in determining dinosaur behavior. Luckily, dinosaur footprints are extremely abundant, and can be found as single prints or as trackways, sometimes hundreds of yards in length. One trackway in central Colorado called the "Dinosaur Freeway" is suspected to continue for hundreds of miles into New Mexico!

Fossil footprints can give scientists insight into a creature’s behavior revealing such information as locomotion, stride and speed, foot and leg anatomy, chronology, ecology, and geographic distribution.

The tracks are found, generally, in three forms: casts, true prints, and underprints. A cast is formed when the original imprint is filled with sediment that hardens into rock. True prints form when the animal leaves a direct imprint in the ground surface it steps on. Underprints are created when the weight and pressure of the dinosaur’s foot causes it to press into layers beneath the thin ground it steps on. Underprints usually don’t contain the detail of foot structure that a true print will sometimes reveal.

Because skeletal remains are seldom found along with tracks, it’s nearly impossible to say which exact species created them, so thanks to Edward Hitchcock fossil footprints have their own classification. The reverend’s original classifications contained genera such as Grallator, Eubrontes, and Anomoepus, but new names continue to be added as new tracks are uncovered. Take for instance, Dr. Phil Manning’s above mentioned recent discovery of a large therapod footprint. Because of its size and structure and the location it was found, it can be speculated that the trackmaker was a Tyrannosaurus rex. But because it’s not certain that that’s the case, the track would be attributed to a T-rex but would be called a Tyrannosauripus, a genus name meaning “tyrant lizard foot”. Dr. Manning could make it more specific by add a species tag resulting in something like Tyrannosauripus manningnensis.

In general, tracks are described by the size and shape of the footprint, the number and arrangement of digits, claw and heel marks, interdigital webbing and skin impression.

Some well-known tracksites in the United States include St. George Dinosaur Discovery Site in Utah, the Red Gulch tracksite in Wyoming, Dinosaur Ridge in Colorado, Dinosaur Valley State Park in Glen Rose, Texas, Clayton Lake State Park in New Mexico, and of course, Dinosaur State Park in Rocky Hill, Connecticut.


Glen Kuban’s great dinosaur track info site
Dinosaur Trackers Research Group – Dr. Martin Lockley
Tracks of swimming dinosaur
Walk like a dinosaur; the study of emus
Raptor tracks show group behavior

Your Comments, Thoughts, Questions, Ideas

Erin1's picture
Erin1 says:

What great information about trace fossils! When people hear "fossil," they immediately think "bone" - but so much more can be revealed about these species' behavior from the other marks they leave behind. When I see a trackway, I can almost see the animals walking's an amazing look into ancient life.

A dig team from the Houston Museum of Natural Science is working at a site that's yielding lots of other kinds of trace fossils - like coprolites and burrows. They've written all about it at their blog - here's the link.

posted on Tue, 11/27/2007 - 4:47pm
mdr's picture
mdr says:

Thanks for the link Erin!

posted on Wed, 11/28/2007 - 2:02pm

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