About the Authors
School of Human and Life Sciences, Whitelands College, Roehampton University, London, United Kingdom
Departament de Fisica, E.P.S. P-II, Universitat de Girona, Campus de Montilivi, Catalonia, Spain
Department of Classics, Colgate University, Hamilton, New York, United States of America
The authors have declared that no competing interests exist.
RP gathered the data (Tables S1 and S2), calibrated the dates, computed the great-circle and shortest-path distances, and prepared Figures 1 and 3. RP and JF jointly prepared the tables, wrote the paper, and prepared Text S1. JF conceived the computation of shortest-path distances, summarized the computation in Text S2, prepared Text S3 and Figure 2, and computed the observed and predicted speed ranges. AJA made suggestions on the interpretation of the results, on the shortest-path distance computations, on the calibration of dates, and on the write-up of the paper.