BIOTIC INVASION AND REGIONAL FAUNAL CHANGE IN MARINE COMMUNITIES DURING LATE PALEOZOIC POSTGLACIAL WARMING IN EASTERN GONDWANA

Climate change is an important driver of species range shifts, increasing the likelihood of biotic invasions that may disrupt the competitive landscape and trigger community restructuring and/or extinctions. Climate-driven geographic range shifts were common in Pleistocene-Recent and late Paleozoic forest ecosystems, but this study is the first to document the regional-scale response by marine taxa to icehouse-greenhouse cycles in the late Paleozoic. Range shifts were documented using a database of more than 3500 fossil collections from the Permian of eastern Gondwana and peri-Gondwana, spanning the earliest Permian acme of the late Paleozoic ice age, major deglaciation, and the Late Permian establishment of an ice-free greenhouse. The climatic affinity of genera was quantified using the mean paleolatitude of their occurrences, allowing taxonomic composition to be used as a paleoclimate proxy. The biogeographic boundary between warm-water and cool-water brachiopod faunas along the northern margin of Gondwana was located at 30-35° S latitude during the Asselian-Sakmarian glacial maximum, consistent with previous reports of a narrow tropical belt during the late Paleozoic ice age. The tropical zonal boundary shifted poleward during the Permian, occurring at approximately 40° S in the Roadian-Wordian and 45° S in the Late Permian, implying widening of the tropics and shallowing of the latitudinal temperature gradient during postglacial warming. Climatic amelioration also allowed warm-water taxa to invade formerly cold-water habitats such as eastern Australia. Tropical brachiopods are unknown from that region during peak glaciation but a major biotic invasion during Artinskian deglaciation resulted in a significant increase in their frequency, even in polar regions such as Tasmania. This faunal invasion coincided with marked restructuring in marine paleocommunities, suggesting that invasion and community change were both driven by climate warming, although invasive taxa may have contributed to destabilization of pre-existing community structure.