Passage II

Fossil footprints of dinosaurs can be used to identify the type, size, speed, and gait of these animals. Determination of gait (the manner of moving on foot) is based on comparisons with speeds at which modern animals walk and run. Geologists performed the following studies to help estimate this information for some ancient footprints.

Study 1

A 68-million-year-old fossil trackway was discovered in a rock formation that consisted of alternating layers of mudstone and sandstone. A trackway is a path or trail commonly used by groups of animals. In the top mudstone layer, five sets of tracks were exposed that belonged to several species of two-legged dinosaurs. The tracks were oriented in the same direction and were formed at approximately the same time. Geologists concluded that two sets were made by meat-eating dinosaurs and the other three sets by plant-eaters. Measurements of the foot length and stride length (distance between successive footprints) of each set of dinosaur tracks were taken at the trackway.

Study 2

A geologist measured the skeletons of meat-eating and plant-eating dinosaurs in a museum. Table 1 shows the leg length, foot length, and ratio of leg length to foot length for those museum specimens.

Study 3

The leg length of the five dinosaurs from Study 1 was estimated using the data from Study 2. Their estimated speed was then calculated from modern animals that have stride-length-to-leg-length ratios similar to those of dinosaurs. Table 2 shows the calculated leg length, calculated speed, and gait of the dinosaurs.