PREVALENCE OF THE LILLIPUT EFFECT AT THE K-PG MASS EXTINCTION

Body size is an important parameter in paleontological studies due to ease of measurement/preservation as well as being a metric shared by all taxa. Reduction in body size after biotic crises have been documented for a wide array of groups found at various Phanerozoic mass extinction events from early Silurian corals to early Danian echinoids (Twitchett, 2007, see also refs therein). This project aims to test the prevalence of this phenomenon termed the 'Lilliput Effect' within the molluscan biota associated with the K-Pg mass extinction. It is hypothesized that rapid evolutionary response to altered selection pressures during mass extinction is the driver. This primary hypothesis will be evaluated against two additional hypotheses of size reduction proposed by Twitchett (2007) and later expounded upon by Harries and Knorr (2009): 1) stunted growth as a response to stressed ecosystems, and/or 2) mass extinctions are size selective. Given that K-Pg sections are globally abundant, this extinction is an ideal event for testing the prevalence of the Lilliput Effect on temporal, taxonomic, and spatial scales. Sample collection in the field entailed bulk sampling of ~2 gallons of material at 10 cm intervals across the K-Pg horizons. The K-Pg boundary is defined after Schulte et al., (2010) where the basal Paleogene includes any impact generated 'event deposits' and the iridium anomaly. Body size is characterized using the geometric mean of the length and height; a metric shown to be highly correlative with more complex morphometrically based size measures (Kosnik et al., 2006). Results include preliminary size measurements from museum samples collected at Braggs Alabama (see: Bryan and Jones, 1989) as well as preliminary carbon isotope values from bulk rock carbon collected at Cotton Mouth Creek at the Brazos River in Texas. Results from FLMNH samples from Braggs Alabama show a decrease in body size for all fauna. However, when size measurements of Ostrea spp. are excluded, the pattern is reversed and a slight increase is noted. Carbon isotope data from Brazos display a negative trend above the 10cm thick iridium bearing boundary clay and return to near cretaceous values at ~1.5m above the boundary. Future plans include adding size measurements from Texas as well as examining size change at the familial level.