An Overview of Dinosaur
Tracking
Introduction
Dinosaur tracks are remarkably abundant in many areas, and provide
rich sources of scientific information on dinosaur behavior,
locomotion, foot anatomy, ecology, chronology, and geographic
distributions. Yet for many years dinosaur tracks were largely
neglected by most paleontologists, who often seemed to view them as
incidental curiosities. Fortunately, this attitude changed
dramatically in recent years. The widespread revival of interest in
dinosaurs has been paralleled by a renewed interest in dinosaur
tracks. Today countless amateur and professional "trackers" are
actively studying track- sites all around the world. New sites are
being discovered at a rapid rate, and track studies are becoming
more detailed and systematic as the scientific importance of tracks
becomes more widely recognized.
Uncovering, documenting, and interpreting dinosaur tracks involves
tools and techniques different from those applied to body fossils,
but the basic principles can be learned and applied by anyone.
Moreover, a number of excellent dinosaur track exhibits are now
available to the public. Standing amid the footprints of these
fantastic prehistoric beasts can be an exhilarating experience.
Some trackways are so fresh-
looking that it is not hard to imagine the trackmakers having strode by only moments
before. Unless the fantasy of cloning dinosaurs becomes a reality,
this is probably the closest we can come to standing beside a
living, breathing dinosaur.
Basic Terms and Definitions
Fossilized
dinosaur tracks are forms of trace fossils, also known as
ichnites or ichnofossils. Unlike body fossils, which
are the remains of dead bodies, trace fossils record the active
movements and behaviors of ancient organisms. Besides footprints,
trace fossils include fossilized burrows, dens, feeding tunnels,
eggs, nests, stomach contents, coprolites (excrement), tooth and
claw marks, and any other product or trace formed while an
ancient organism was still alive. The study of trace fossils
is known as ichnology. Some
workers restrict the term to mean the study of fossil traces.
Others include both modern and ancient traces, using the term
paleoichnology to specify the
study of ancient traces. At any rate, the study of modern traces
often helps in interpreting ancient traces.
The terms track, print, footprint and footmark are often used interchangeably,
although the first two include footprints as well as marks from
other body parts, such as a tail, snout, or belly. A series of two
or more consecutive tracks by the same animal is known as a
trackway or
trail.
Information from Dinosaur Tracks
Some of the most direct information available from dinosaur tracks
concerns locomotion. Trackways
can indicate whether a dinosaur was walking, trotting, running, or
wading. They also show whether the animal was traveling in a
bipedal (two-legged) or quadrupedal (four-legged) manner, or
altering its gait between these modes. One can also calculate
approximately how fast the trackmaker was moving. Additionally, tracks
tells us how a trackmaker
carried its tail, whether it walked with a narrow or sprawling
gait, and in some cases, what posture the animal assumed while
resting.
Inspection of individual prints provides data on the size and shape
of the trackmaker's feet, and
the number the toes. Clear prints can even reveal details of the
soft anatomy of the foot, including the pattern of pads and muscles
on the feet, and the flexibility of the digits. These track
features, combined with trackway patterns, reveal important clues
about the identity of the trackmaker.
Tracks also provide clues about the social behaviors of dinosaurs,
and the environment in which they lived. Some sites contain dozens
of parallel trails heading in the same direction, indicating a
herding or migratory behavior. Often such trails seem to indicate
the position of an ancient shoreline. Other sites indicate several
herbivores clustered around apparent tree impressions, suggesting a
feeding group. One interesting site has been interpreted by some as
recording an ancient chase scene. Another site appears to record a
dinosaur "stampede" (Thulborn,
1990).
Tracks also complement body fossils in providing information about
geographic distributions of dinosaur groups, as well as their
chronologic ranges. Knowledge of ancient ecology and population
biology can also be expanded by studying dinosaur tracks. For
example, researchers may tabulate the ratio of carnivore to
herbivore tracks in a region, or the proportions of large to small
trackmakers.
How Dinosaur Tracks are Formed
Unlike body
fossils, which often are best preserved when they are buried
rapidly, tracks are more likely to be well preserved when they are
buried in a relatively slow, calm manner. For this reason, tracks
and bones are seldom found in close association.
There are two main ways in which tracks can be formed and
preserved. The classic scenario is as follows. First, a
trackmaker walks along a moist
but firm, fine-grained sediment. Then the tracks remain exposed for
a short while, allowing them to become drier and harder (and thus
able to resist damage during subsequent burial). A short time later
the prints are gently buried with additional sediment, preferably
of a contrasting type (which would allow the layers to separate
when later reexposed). While
buried for millions of years, the original sediment lithofies (turns into rock). Finally, the
tracks are reexposed in modern
times by erosion or other forces. Of course, the tracks also must
be found and studied before they are destroyed by weathering,
quarry workers, or other dangers. Tracks formed under less ideal
conditions tend to be distorted or indistinct, if preserved at
all.
Recent research suggests another mechanism of print formation,
which involves a dinosaur walking on a very soft surface. In such a
case, the animal's feet may push into firmer layers below the
surface. The soupy surface material may then rush back over the
upper depressions, simultaneously covering the prints made in the
lower layers. The subsurface prints are known as underprints, undertracks, or ghost tracks. Because they
are buried as soon as they are made, any erosion or other
destructive forces occurring at the surface would pose no threat to
them, increasing their chances of being preserved.
Figure 1
A. Track Formation and
Preservation
Diagram showing a true track, natural cast, undertracks, and track infillings as they might appear in rock
strata. Adapted from Lockley
(1991).
B. Track Variations Related to Sediment
Consistency.
All the tracks shown were made by a single dinosaur stepping on
substrates of different concistencies, with the firmer substrates
at left and the softer ones on the right. Notice the absence of
distinct pads in the deeper prints (at right). The right-most track
suffers from "mud collapse" or "mud back-flow," where soft sediment
slumps back into a track depression, distorting its shape. Adapted
from Thulborn (1990).
C. Basic Trackway
Measurements.
Pace angles (also called step angles or pace angulations) may be calculated using
trigonometry once pace and stride measurements are made. On a
quadruped trackway, these
measurements should be made for both rear and front prints. One
should also measure individual print lengths, widths, depths, and
digit dimenstions and
angles.
Major Types of Dinosaur Tracks
It is often difficult or impossible to identify the
particular genus or species of dinosaur that made a given
trackway. However, one can
usually determine at least the general group of dinosaurs to which
the trackmaker belonged, since
foot structures vary considerably among different dinosaur groups.
In many cases the locomotor styles of different groups varied as
well.
Paleontologists divide dinosaurs into two main groups based largely
on hip structure: Orithischians
and Saurischians. However, when
dealing with tracks, it is more convenient to first determine
whether a trackmaker is bipedal
or quadrupedal (Ornithischians
and Saurischians both included
bipedal and quadrupedal members).
Bipedal trackways are the most
common. They contain left-right sequences of similarly shaped
prints, each containing three major digit marks. They are commonly
called "three-toed tracks" or tridactyl tracks. Most bipedal dinosaurs
actually possessed four digits on each foot, but one digit (the
hallux) was small and held in
an elevated position at the inside rear of the foot. When recorded
at all, hallux marks are
usually small and shallow.
Dinosaurs that made bipedal tracks fall into two major
groups: theropods (bipedal
meat-eating dinosaurs) and ornithopods (bipedal plant-eating
dinosaurs). Theropod tracks
typically exhibit relatively long and narrow digit impressions,
terminated with sharp, slender claw marks. The posterior ends are
typically somewhat V-shaped. Among theropods, a somewhat arbitrary division is
made between small, gracile
forms called coelurosaurs, and
large, robust forms known as carnosaurs. Coelurosaur tracks often exhibit digits
held closely together, and distinct toe pads. The shapes and
positions of the pads are useful in identifying particular
ichnogenera. The digit marks of
carnosaur tracks are often more
widely splayed and robust, with less distinct
pads.
Text taken from:
An Overview of Dinosaur Tracking;Originally published in the April
1994 M.A.P.S. Digest, Mid-America Paleontology Society,
Rock Island, IL.
A youth cooperative currently oversees the dinosaur footprints and
guide tourists to the site. A donation is greatly
appreciated.
Questions:
1. Describe in your own words how you think the track was formed in
the underlying rock.
2. There are two
distinct tracks of dinosaurs in the river bed. The questions below
pertain to the smaller of the tracks.
a.) Describe the size, depth and form of these fossil dinosaur
footprints. Do you think the underlying substrate was firm, soft or
muddy when the dinosaur walked across it?
b.) From your answers above, estimate what type of dinosaur it was
and what it might have been doing when it made these footprints.
Explain what observations lead you to this conclusion.
4. Please take a photo of yourself at published co-ordinates
(optional)
Please log your cache after your visit, and email me your answers.
I will contact you should your answers not be
correct.