Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, RI 02912, USA.
Proc Natl Acad Sci U S A. 2011 May 31;108(22):8972-7. doi: 10.1073/pnas.1102473108. Epub 2011 May 13.
Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by "semiprecessional" (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5-20 °N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.
尽管大陆合并成了单一的陆地板块盘古大陆，但晚三叠世的陆地四足动物组合却令人惊讶地具有地域局限性。在北美洲东部，我们表明，以横齿兽类合弓兽为主的组合仅限于一个持续了超过 2000 万年的湿润 6°赤道带，其特征是“半前进性”（约 10000 年）气候波动，在湖泊地层的稳定碳同位素和沉积相中有反映。更干旱的 5-20°N 地区保存了以原鳄形目动物为主的动物组合，与大约 20000 年的气候循环的表达更为强烈有关。在没有地理障碍的情况下，我们假设，这些天文强迫的气候表达的变化产生了纬度气候带，这些气候带可能通过排泄生理学，将陆地脊椎动物分类为不同的生物地理区系，追踪纬度，而不是地理位置，因为原北美板块向北平移。尽管由于缺乏地理障碍，人们通常认为早中生代的特点是全球分布的陆地动物群落，但实际上地域局限性是常态，只有在大规模生态破坏之后，才会出现几乎全球的群落。
