Chapter 7 – Basic Information about Dinosaur Tracks
The Importance of Dinosaur Trace
Fossils
Advantages
Potentially more abundant than other
dinosaur fossils
A dinosaur has only one skeleton, but can make many trace fossils
May be preserved
in rocks that do not normally preserve dinosaur body fossils
Directly reflect in situ dinosaur behavior
A dinosaur was alive when it made the trace fossil
Dinosaur behavior interpreted from
trace fossils
Where and in what environments they
preferred to roam
Individual of group movements in
response to these environments
Interactions among dinosaurs of the
same species or different species
Approximate speeds of movement
Their most likely posture
Miscellaneous
Useful in biostratigraphy in the
absence of body fossils to indicate the presence of dinosaurs
Can help determine if any dinosaurs survived into the Tertiary
Useful in Paleobiogeography
Can help determine the spatial distribution of particular dinosaur
groups
Soft-part anatomy revealed by
well-defined footprints
Definition of Track Terms
See Figure 7.1
Length and width of track, number of
digits, digit width and length, angles between digits, depth of penetration of
the track or individual claws, number of fleshy pads associated with digits,
width and height of any visible deformation around the track
Trackway – a series of two or
more successive tracks made by the same foot
Stride length, pace length, straddle,
pace angulation (180 degrees is a straight line)
Confirm that dinosaurs walked with their legs under their bodies
Obligate vs Facultative
Obligate – walk only in one way
Facultative – the ability to
walk a different way from normal if needed
Theropods and pachycephalosaurs were obligate
bipeds; some ornithopods were facultative quadrupeds; stegosaurs and some
sauropods were facultative bipeds; ankylosaurs and most ceratopsians were
obligate quadrupeds
Quadruped tracks
Walking often leaves right-left pairs
of foot impressions with a pes track just in back of or overlapping the
posterior edge of a manus track
Much different pattern for running
animals
At least eight running theropod trackways; only one quadruped – a Late Cretaceous ankylosaur
from Bolivia
Dinosaurs mostly walked
Direct register – same-side pes
placed into the preceding manus print
Usually discernable only if the manus is bigger than the pes, as for brachiosaurs
Information from Single Footprints
Pressure-release features
Foot applies pressure against the
surface surrounding the track and the release of that pressure
Can indicate the general direction of movement, or whether the animal stopped and
looked in certain direction, moved
backward, or was carrying
something
Bioglyph
Detailed body impression made by a
tracemaker in association with a trace fossil
Can be skin or toe-pad impressions
Compression Shape
Not-so-well-preserved tracks leave
geometric outlines
Can distinguish the major groups of dinosaurs
Taphonomy of tracks
Tracks must be buried
Undertracks
An impression made on a substrate
below the surface (see Figure 7.8)
Preservation Factors
Moistness of the sediment
Too little or too much either results in no impressions or impressions
that collapse on themselves
Grain size of the sediment
Fine-grained sediments are better than coarse-grained sediments
Cohesiveness of the sediment
Depends on clay content
Best preservation in fine-grained
sediments with just enough water to make them cohesive
Variations in the substrate along a
trackway can result in “missing tracks” (see Figure 7.5)
Most dinosaur tracks are preserved
as undertracks
Not a detailed record of the anatomy
of the foot or dinosaur behavior
Molds vs Casts
Impressions into the surface or a
subsurface substrate form molds
Casts of the track are produced when
sediment of different grain size fill the mold, such as sand filling a track
made in mud
Classification of dinosaur track types
Things to keep in mind
Not always easy to match a track made
by a fleshed out foot with the bones of the foot that are all that make up the
fossil record
Tracks may have been made by an
unknown species of dinosaur
Confusion between tracks of juvenile
dinosaurs of one species with those of small adults from another (but
morphologically similar) adult species
Classification criteria
Number of toes, track size, presence
or absence of claws, number of feet used
Can broadly distinguish theropods,
ornithopods, prosauropods, sauropods, ankylosaurs, stegosaurs and ceratopsians
- see Figure 7.6
Theropod tracks are exceeding common in some strata throughout the
entire geologic range of dinosaurs
Ankylosaur and stegosaur tracks are rarely reported from any strata
Tracks given Ichnogenus and
ichnospecies names (ichnotaxa)
Problems with naming a track after its inferred trackmaker – a different dinosaur made have
made the track
Problems with naming tracks made by a single dinosaur moving across a
surface of varying substrates that produce different track morphologies – should each different track
morphology be given a different name?
Problems with synonomy
Dinosaur Behavior Indicated by
Tracks
Individual Dinosaur Behavior
Track maps should be made
Calculating speed
Uses a mathematical technique based on
empirical data from living animals
Uses the stride length and footprint
size in dinosaur trackways together with the leg length (hip height) measured
from dinosaur skeletons
Stride length increases with speed
Relative Stride length is the ratio of
the stride length to the leg length
Necessary because a shorter individual has a shorter stride length and
will take more steps than a taller individual moving at the same speed
It’s a dimensionless number – no units
Stride length measured directly from a trackway
Leg length estimated by the foot length, with leg length 4.5 to 5.5 times longer than foot length
Depends on dinosaur group and dinosaur size (small theropods 4.5, large theropods 5.5)
Dimensionless speed is the ratio of
the speed to the square root of the leg length times gravitational acceleration
Necessary because a smaller individual has a slower speed than a
larger individual for the same relative stride length
It’s also a dimensionless number
An estimate for actual speed of a dinosaur
can be obtained from the plot in Figure 7.7
Relative stride length is calculated from a trackway, the
dimensionless speed is read from the graph, and the actual speed estimate is
the dimensionless speed times the square root of the estimated leg length times
gravitational acceleration
Note the units are meter per second and must be converted to kilometers per hour
Most estimates show that dinosaurs
were walking at a not very brisk rate
Fastest speeds are about 40 km/hr (25
mph) for small- to medium-sized theropods
Behavior of Multiple Dinosaurs
Kinds of behavior deduced from
multiple trackways on the same horizon
Whether the dinosaurs were moving as
individuals
Shown by parallel trackways with movement in opposite directions
Whether the dinosaurs were moving as a
group (herd, pack, flock)
Shown by parallel trackways that are equally space with movement in
the same direction and at the same speed
Sauropod trackways in the Late Jurassic Morrison Formation of southern
Colorado
Early Cretaceous “stampede” of small theropods away form a
large theropod
Things to keep in mind
Tracks on a single horizon could have been made over the course of
days or months
Some tracks on a horizon could be undertracks made years later
Dinosaur Behavior Not Indicated by Tracks
Tail dragging
Swimming
Previous view that sauropods and
hadrosaurids had to be aquatic
Roland T. Bird interpreted a trackway
with only manus impressions as a result of swimming, but reexamination of the
trackway showed they were undertracks and the pes impressions were not
preserved
Obligate quadrupeds rearing up on
their hind legs
Intraspecific competition or
interspefic confrontations
Some trackways suggest sauropods being
followed by theropods
Roland T. Bird interpreted one trackway
where the theropod tracks ended where they converged with the sauropod tracks
as an attack by the theropod in which it leaped on the sauropod – no
response from the sauropod however
Incredible stride lengths
suggesting very rapid speed or very large dinosaur
Some tracks were missed in the initial
study
Hopping, Galloping or Walking
Backward
Other Paleoenvironmental Information
Gained from Dinosaur Tracks
Effects on Sediment, Plants and
Anything Unfortunate Enough to Have Been Stepped on by a Dinosaur
Bioturbation
Sediment disturbance by organisms
– “dinoturbation”
Trampling – repeated passage of
large animals – crushed bivalves and bones