FIRST COMPARISON OF LATEST CRETACEOUS AND EARLY PALEOCENE INSECT DAMAGE IN THE SOUTHERN HEMISPHERE SUPPORTS A PATAGONIAN BIODIVERSITY REFUGIUM

In the western USA, insect feeding-damage diversity on fossil leaves decreased significantly across the Cretaceous-Paleogene (K‒Pg) boundary as a result of the Chicxulub impact. However, little is known about plant-insect associations across this interval in the Southern Hemisphere. We present preliminary results comparing insect damage on latest Cretaceous with early Paleocene fossil floras from coastal deposits in Chubut Province, Patagonia, Argentina, the first such study done outside the western USA. We compared ca. 1000 leaf fossils from two sites in the late Maastrichtian Lefipán Formation in northwestern Chubut to approximately 2000 leaf fossils from two sites in the Danian Salamanca Formation, located ca. 360 km to the southeast (~50° south paleolatitude).

Insect damage on both the Cretaceous and Paleocene floras appears more diverse than North American analogs and includes many new associations. Examples of new fossil damage types from the Lefipán Formation are spheroidal galls on primary veins surrounded by a wide rim of thickened woody tissue, and ellipsoidal to spheroidal galls composed of carbonized material with striated surfaces. Most early Paleocene plant localities from the western USA are associated with low plant and damage type diversity and a homogenous, generalized composition across sites. In contrast, the Paleocene Salamanca floras are associated with high damage type diversity and a number of new damage types. Examples include concentric rings of piercing and sucking marks, small holes surrounded by dark, blotched reaction tissue, and mines and two gall types on the oldest known Agathis. These preliminary results suggest that extinction of insect herbivores at the K‒Pg boundary was less severe or recovery was more rapid in southern South America compared to previously studied North American analogs. High early Paleocene damage diversity, combined with earlier work demonstrating minimal overall pollen extinction across the K‒Pg boundary in the Lefipán Formation, supports an emerging hypothesis that southern latitudes were buffered from the global environmental disaster after the end-Cretaceous impact. This buffering provided a refugium for associational diversity, as well as the survival of a long list of nominally Mesozoic plant and vertebrate clades.