DINOSAUR BIOGEOGRAPHY: MIGRATION PATHWAYS AND REFUGIA

Dinosaurs were terrestrial travelers. They did not travel by air or sea, only by land relying on “land-bridges” to connect them to distant places. Land-bridges, in turn, were controlled by mountain building events (on timescales of 10’s of my), plate tectonic events like continental rifting and collision (also on timescales of 10’s of my), and changes in sea-level (eustatic events, 100,000’s yrs). The most important factor controlling dinosaur migration pathways was eustatic events. “Connectivity” between distant places was high during lowstands (when sea level may have fallen to the edge of the continental shelves) and low during highstands (when sea level may have been 200-300 meters higher than today). During sea level highstands dinosaurs were isolated on numerous “continental island refugia”.

There were two types of continental island refugia: “temporary or highstand” refugia which were reconnected during lowstands of sealevel (e.g. eastern and western North America), and “permanent or island” refugia which were isolated during times of high and low sealevel (e.g., Madagascar). Evolutionary exchanges regularly occurred between temporary refugia. Evolutonary exchanges rarely occurred between permanent refugia.

“Paleogeographic connectivity “ is defined as geographic distance between the geographic centroids of each highstand refugia. The faunal similarity between two highstand refugia will be a function of the paleogeographic connectivity (and other factors such as paleoclimatic barriers). Using paleo-digital elevation models from the PALEOMAP PaleoAtlas and estimates of sealevel change from Haq (1987), highstand refugia were mapped for four intervals during the Cretaceous (Maastrichtian, Cenomanian/Turonian, early Aptian, and Berriasian). Using the ArcGIS tool, Spatial Analyst, “cost weighted distance maps” and “least cost migration paths” were constructed that illustrated the mostly likely paths of dinosaur migration between these temporary refugia. The number of dinosaur migration pathways (DMP) between the temporary refugia was calculated to be, DMP = (n2 -n)/2, where n is the number of temporary refugia. It was noted that some of the dinosaur migration pathways predicted by this analysis correspond to known dinosaur trackways (e.g. North Slope of Alaska).