TRACKING PALMS IN THE FOSSIL RECORD: IMPLICATIONS FOR RECONSTRUCTING PALEOENVIRONMENTS, PALEOCLIMATES, AND EVOLUTIONARY HISTORY

Palms (Arecaceae) are abundant in many modern low-latitude terrestrial ecosystems, and are notably common in the southeastern USA. While they are dominantly equatorial in biogeographical distribution today, their macrofossil record extends back to Cretaceous time and, during some periods of Earth’s climatic history, into polar and sub-polar paleolatitudes. Much recent work on the evolution, systematics, historical ecology, and biogeography of modern palms has shed light on the group's evolutionary origins, ecological interactions, and environmental history. What deserves more study, however, is the global fossil record of this group in space and time and how that record relates to paleoclimate and other paleoenvironmental data.

More than 300 palm macrofossil occurrences from >200 localities around the globe are reported in the published literature and these were collected in a database. The reported genus and species occurrences comprise >60 leaf, fruit, axis, and inflorescence genera overall. Locality information for each occurrence includes the stratigraphic formation, age reported in the literature, age constraint, lithology of fossil preservation, the locality’s modern geographic coordinates, and its rotated paleogeographic coordinates to the reported literature age.

Analyses of the database show the greatest paleolatitudinal extent of the palm macrofossil record to be during Early Paleogene time, with occurrences spanning more than 100 latitudinal degrees. The paleolatitudinal span of the record then constricts toward more temperate and subtropical distribution through Late Paleogene and Neogene time. The data show a bimodal paleolatitudinal distribution in northern subtropical-temperate and southern subtropical bands when totaled across Cretaceous to Pleistocene occurrences. This occurrence pattern contrasts with the predominantly equatorial distribution of palm diversity today. Analysis of co-occurring fossil plant groups and sedimentological indicators of environments of deposition can assist us in understanding environmental tolerances and preferences of ancient palms as well.

Understanding the paleobiogeographical record of these iconic plants can help elucidate Earth’s paleoclimatic and paleoenvironmental history and provide context for modern global change.