The Beginning of the Mesozoic: Paleoecological and Paleo- environmental Analysis of the Lower Triassac Virgin Limestones (Nevada and Utah)

二叠纪末期的大规模灭绝被确定为自后生动物生命起源以来地球生物圈经历的最大扰动。尽管人们对这次物种大灭绝的原因知之甚少，但对其后果的生物条件或从这次事件中生物恢复的本质所知就更少了。在二叠纪结束后沉积的下三叠统Moenkopi组(内华达州南部和犹他州西南部)的Virgin段中的动物群和石灰岩化石，为了解浅海碳酸盐环境中的底栖动物群在这一恢复阶段的表现提供了机会。对维尔京石灰岩的初步研究表明，沉积在正常的海洋环境中，海底大型无脊椎动物组合的物种丰富度相对较低。具有潜在重要意义的是看起来正常的海洋叠层石间隔，这可能是由于大规模灭绝导致的食草动物限制，从边缘海洋避难所暂时扩展到正常海洋环境。从危机中幸存下来的一些未知的古生代半月体进化而来的大量有关节的海绵体标本的存在，证明了恢复的开始。研究将阐明生物群如何从大规模灭绝中恢复过来。

The mass extinction at the end of the Permian has been established as the greatest perturbation which the Earth's biosphere has experienced since the origin of metazoan life. Although relatively little is known about the cause of this mass extinction, even less is known on biotic conditions in its aftermath or the nature of biotic recovery from this event. Fossil faunas and limestones in the Lower Triassic Virgin Member of the Moenkopi Formation (southern Nevada and southwestern Utah), deposited 5 my after the end of the Permian, present an opportunity to learn how benthic faunas in shallow marine carbonate environments were faring in this recovery interval. Preliminary study of the Virgin limestones indicates deposition in a normal marine environment with benthic macroinvertebrate assemblages of relatively low species richness. Of potentially great significance are intervals of apparent normal marine stromatolites, which may represent temporary expansion from marginal marine refugia into normal marine settings due to restriction of grazers, caused by the mass extinction. Evidence for the beginning of recovery is demonstrated through the presence of abundant specimens of the earliest articulate crinoid, which had evolved from some unknown Paleozoic inadunate that survived the crisis. Research will illuminate the way in which biotas recover from mass extinctions.