BIOGEOGRAPHIC PATTERNS OF AGELEODUS ACROSS THE END-DEVONIAN MASS EXTINCTION

Recent descriptions of Devonian and Carboniferous vertebrate faunas have advanced our understanding of the ecological structure of early vertebrate-bearing fresh to brackish water ecosystems and have shed light on the biogeographic patterns of taxa during this time. Significant faunal reorganization occurred as the result of the end-Devonian extinction and continued well into the Carboniferous. Similarities have been identified among contemporaneous Carboniferous chondrichthyan assemblages across Laurussia and in the Australian portion of Gondwana. These assemblages include xenacanthoids and hybodontiforms, as well as the poorly known taxon Ageleodus, all thought to be small-bodied, nibbling sharks. The cosmopolitan distribution of this assemblage suggests it may represent a post-extinction recovery fauna, and that Ageleodus is a recovery taxon. The small body size of these taxa may have been an advantage in the early Carboniferous as post-Devonian extinction environments may have selected for reduced body sizes among jawed vertebrates.

Ageleodus is known from two definitively dated Famennian localities, Red Hill in Pennsylvania and the Pripyat Trough in Belarus. It is known in both western (Mole Hill) and eastern Europe (Andreyevka-1), with a range extension into Gondwana (Mansfield, Australia) during the Tournaisian. During the Viséan through the Moscovian it becomes increasingly common in North American faunas while still known from Europe and Australia through the Viséan.

The cosmopolitan distribution of Ageleodus likely acted as a buffer against extinction risk for the taxon through the end-Devonian mass extinction as geographic range has been shown to decrease extinction risk. Increased examination of Devonian-Carboniferous faunas in the last few decades has indicated that many of the environments these organisms inhabited were not freshwater as had previously been thought, but instead were either brackish or potentially fully marine. Depositional environments of assemblages containing Ageleodus have been interpreted across a variety of environments from fresh water through fully marine. Its broad environmental tolerance likely contributed to its cosmopolitan distribution and may have provided for refugia during the end Devonian extinction.