The Upper Cretaceous Western Interior Basin of North America provides a unique laboratory for constraining the effects of spatial climate patterns on the macroevolution and spatiotemporal distribution of biological communities across geologic timescales. Previous studies suggested that Western Interior Basin terrestrial ecosystems were divided into distinct southern and northern communities, and that this provincialism was maintained by a putative climate barrier at ∼50°N paleolatitude; however, this climate barrier hypothesis has yet to be tested. We present mean annual temperature (MAT) spatial interpolations for the Western Interior Basin that confirm the presence of a distinct terrestrial climate barrier in the form of a MAT transition zone between 48°N and 58°N paleolatitude during the final 15 m.y. of the Cretaceous. This transition zone was characterized by steep latitudinal temperature gradients and divided the Western Interior Basin into warm southern and cool northern biomes. Similarity analyses of new compilations of fossil pollen and leaf records from the Western Interior Basin suggest that the biogeographical distribution of primary producers in the Western Interior Basin was heavily influenced by the presence of this temperature transition zone, which in turn may have impacted the distribution of the entire trophic system across western North America.

中文翻译：

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北美上白垩统西部内陆盆地极端气候梯度引起的生态区划

北美上白垩统西部内陆盆地提供了一个独特的实验室，用于限制空间气候模式对跨地质时间尺度的生物群落宏观进化和时空分布的影响。先前的研究表明，西部内陆盆地陆地生态系统被划分为不同的南部和北部群落，这种地方性是由大约 50°N 古纬度的假定气候障碍维持的；然而，这种气候障碍假说还有待检验。我们提供了西部内陆盆地的年平均温度 (MAT) 空间插值，证实了在白垩纪的最后 15 年期间，在 48°N 和 58°N 古纬度之间存在 MAT 过渡带形式的明显陆地气候屏障. 这个过渡带的特点是纬度温度梯度陡峭，并将西部内陆盆地分为温暖的南部和凉爽的北部生物群落。对来自西部内陆盆地的化石花粉和叶子记录的新汇编的相似性分析表明，西部内陆盆地初级生产者的生物地理分布受到该温度过渡带存在的严重影响，这反过来可能影响了整个北美西部的营养系统。