Douglas J. Nichols M. Attrep Jr. C. J. Orth Kirk R. Johnson 1989 <p>Theories t<span>hat explain the extinctions characterizing the Cretaceous/Tertiary (K/T) boundary</span>^1-3<span>&nbsp;need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction</span>^4-12<span>, but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution</span>¹³<span>, but have previously lacked the sample size and stratigraphic spacing needed to resolve latest Cretaceous floral history</span>^5,14-18<span>. We have now combined megafloral data from a 100-m-thick composite K/T boundary section in North Dakota with detailed palynological analysis. Here the boundary is marked by a 30% palynofloral extinction coincident with iridium and shocked-mineral anomalies and lies&nbsp;</span><span class="stix">∼</span><span>2 m above the highest dinosaur remains. The megaflora undergoes a 79% turnover across the boundary, and smaller changes 17- and 25-m below it. This pattern is consistent with latest Cretaceous climatic warming preceding a bolide impact.</span></p> application/pdf 10.1038/340708a0 en Nature High-resolution leaf-fossil record spanning the Cretaceous/ Tertiary boundary article