VIRTUAL FOOTPRINTS: CREATING DIGITAL MAPS OF DINOSAUR TRACKS AND SEDIMENTARY STRUCTURES

Fossil footprints are an important area of study for understanding animal behavior. To study these footprints and to get a better understanding of the behavior they represent, high quality maps are required. This means shifting away from the stylized maps using generic track shapes to more sophisticated digital maps which preserve actual track morphology.

We developed a method using georeferenced photographs to create scaled maps of tracks and trackways. None of the photographs overlap. Rather, once georeferenced, they create a scattered mosaic of pertinent features which maintain proper spatial relations and scale. For each photograph, we surveyed ground control points (GCP) using a reflectorless total station. The GCP consisted of known points on a compass aligned to geographic north placed next to a feature of interest. We tied the total station survey into a georeferenced frame using two locations determined with differential GPS receivers.

We tested our mapping method at the Dinosaur Footprint Reservation near Holyoke, MA. At this Jurassic aged site we mapped 135 of the over 1000 dinosaur tracks, as well as 12 ripple marked zones. We georectified each photograph using the GCP, allowing us to construct a unified digital map of the site from which we could measure tracks, ripple marks and plant fossils. With these maps, we have collected measurements of the tracks including orientations, widths and lengths. The measurements have been checked for accuracy by taking advantage of the scale on the compass. We find errors in length on the order of a few mm (0.01-0.05 cm) while the orientations show a +/- 2 degree error. Manual measurements of track shape and ripple crest can be assigned to various data types in GIS, and this facilitates rendering characteristics including size, track type and preservation effectively with color, line styles, etc.

This methodology is broadly applicable for macro-sized features and will soon be tested with smaller scale features.