DINOSAUR TRACKS

Reading assignments

• Martin
• Chapter 7: pp. 148-171.

ICHNOLOGY

• the study of trace fossils
• An introduction to ichnology by Anthony Martin
  • dinosaur trace fossils
• An Overview of Dinosaur Tracking
• Trackways from the Hooper Virtual Museum
• Dinosaur Tracks and Traces from Dino Russ

Track

• The impression left by a foot in a sediment or other substrate

Trackway 

• Two or more consecutive footprints belonging to a particular animal progressing in a given direction
• Tracks and track ways may provide the following types of information about dinosaurs:
1. Individual Dinosaur Behavior
   1. Size.
   2. Speed.
   3. Posture
   4. Idiosyncracies, e.g., resting, trailing, etc.
2. Group Behavior
   1. herding characteristics
   2. pack hunting
   3. Interactions between species
3. Types of dinosaurs living in an area when no bones are preserved.
4. Information about past environments preferred by dinosaurs

Dinosaur Behavior Not Indicated by Tracks

1. Habitual tail dragging
2. Swimming or constant immersion in water
3. Obligate quadrupeds rearing up on their hind legs 
4. Intraspecific competition 
5. Interspecific confrontations

Dinosaur Stride Length and Speed

• Dinosaur Tracks: From Stride to Leg Length to Speed
• Kayenta Trackways by Christina Beringer
• Dinosaur Trackways Exercise
• Dinosaur Gaits and Estimates of Speeds
• Pace and Stride length from Brooklyn College
• Jeep-chasing Dinosaurs from Brooklyn College
• Dinosaur Speed Calculator
• Trackway Speeds
• How fast could T. rex run

Martin: pages 162-165

Stride Length

• In a trackway, the distance between two successive steps made by the same foot.
• Stride length is related to leg length
• For a given individual, the greater the stride length, the greater the speed.
• A shorter individual has to take more steps to equal the velocity of a taller individual. [stride rate = steps/unit time]

Relative Stride Length (s_r)

• s_r = s_l / l_l 
  •  where s_l = Stride Length and l_l = Leg Length for each animal.
• Note: (s_r) is a dimensionless number
• s_r normalizes for differences in leg length.  
  • A shorter individual will have a shorter stride length than a taller individual, even if both are moving at the same speed.  The shorter individual will have a greater stride rate.
•   s_l  can be measured directly from the trackway.
•   l_l can be measured from from dinosaur skeletons and equals the distance from the ground surface to the acetabulum of the pelvis. 
  • However, in most cases it is not known exactly which dinosaur made the footprint. 
  • Even if the species is known, the size of the individual making the trackway is likely different from the size of the known skeleton(s).
  • Paleontologists have developed a formula for estimating leg length from footprint length.
  • l_l = f_l * (C), where f_l is the measured footprint length and C is a constant empirically determined by measuring the ratio of leg length to foot length from known skeletons.
    • The value of C varies depending on the kind of dinosaurs.  Some paleontologists have calculated C = 4.0, others C = 4.5 for small theropods, others C = 5.5 for large theropods.
  • Martin (page 162) suggests using an average value of 5.0
    • For example, if a footprint is 45 cm long, the leg length = 45 cm * 5 = 225 cm
    • Using C = 4, l_l = 180 cm.  If C = 5.5, l_l = 248 cm.
• s_r = s_l / l_l 
  • If a dinosaur had a stride length of 307 cm and a leg length of 225 cm
  • the relative stride length = 307 cm /  225 cm = 1.4
    • the greater the stride length, the greater the speed.

• Dimensionless speed (v_d) accounts for variation in overall body size.
• A smaller dinosaur with the same relative stride length as a larger dinosaur will have a lower velocity.
• Dimensionless speed can be determined graphically from relative speed length using the graph on page 164 (Figure 7.7)
•  v_d is related to the actual speed (v) by the following formula
  •  v_d = v /  (l_l * g)^1/2
  • where  l_l = leg length in meters and g = gravitational acceleration = 9.8 m/sec/sec
• rearranging the equation, solve for v
  •  v = v_d  * (l_l * 9.8 m/s²)^1/2
  • for our dinosaur with s_r = 1.4, figure 7.7 indicates v_d = 0.45
    • v = v_d  * (l_l * 9.8 m/s²)^1/2
    • v = 0.45 * (2.25 m * 9.8 m/s²)^1/2 = 0.45 * 4.7 m/s =2.1 m/s = 7.6 km/h
• The fastest speeds estimated from trackways are about 40 km/h for small and medium-sized theropods.