Implications of discoveries of the shovel-tusked gomphothere Konobelodon (Proboscidea, Gomphotheriidae) in Eurasia for the status of Amebelodon with a new genus of shovel-tusked gomphothere, Stenobelodon

Abstract

ABSTRACT Amebelodon and Konobelodon are two members of a group of proboscideans called shovel-tusked gomphotheres. The phylogenetic relationship between them is uncertain, with some authors considering them to be closely related taxa while others consider them only distantly related. This uncertainty stems from confusing issues related to morphology, biochronology, and biogeography. Contributing to this confusion, Amebelodon consists of two distinct morphotypes that do not obviously resemble each other. One, typified by A. floridanus, possesses a conservative dentition and lower tusks, while the other, represented solely by A. fricki, possesses an advanced dentition and lower tusks that closely resemble those found in Konobelodon. In a traditional evolutionary scenario involving these taxa, conservative Amebelodon appeared in North America during the latest Miocene and gave rise to advanced Amebelodon. Advanced Amebelodon in turn gave rise to Konobelodon, with Konobelodon then dispersing into Eurasia. However, new discoveries of Konobelodon in the Late Miocene of Europe and Asia render this hypothesis implausible, and suggest rather that Amebelodon first appeared in Asia during the Late Miocene, where it gave rise to Konobelodon. These findings in turn suggest that A. fricki in North America represents an immigrant from Eurasia. If this new hypothesis is correct, then the status of the conservative species such as A. floridanus within Amebelodon becomes problematic, with the implication that Amebelodon is polyphyletic. On this basis as well as extensive morphological differences, one of these conservative species, Amebelodon floridanus, is here referred to a new genus, Stenobelodon.