Survivorship and recovery of early triassic tetrapods following the permo-triassic extinction event

在已知的五次大灭绝事件中，二叠纪-三叠纪灭绝事件被一致认为是地球历史上最严重的一次。普遍的观点是，70-90%的物种在2.51亿年前灭绝。这种高物种死亡率的估计是基于对低分类分辨率（科级群体）的基于等级的研究。我自己的调查，使用更高分辨率的系统发育研究（种和属），表明陆生脊椎动物（四足动物）在二叠纪-三叠纪灭绝事件中经历了低灭绝压力。到目前为止，我已经研究了羊膜动物（哺乳动物、爬行动物、鸟类和它们的化石亲戚）在二叠纪-三叠纪边界的存活情况。被研究的两个爬行动物类群，原音像类拟肢类和始祖类拟肢类，分别表现出大约29%和14-17%的灭绝。目前对头足类（一组突触类羊膜动物）的研究表明，它们经历了43%的灭绝。从已发表的系统发育学来看，犬齿兽突触类灭绝了40-50%。到目前为止的证据表明，羊膜动物的灭绝并不像人们普遍认为的那样严重，而且灭绝的影响甚至没有传递给这些群体。在南非的卡鲁盆地，原音音类动物和兽头类动物的种类最为丰富，是继水龙类动物之后最常见的羊膜动物。南非拥有研究这次灭绝事件对四足动物影响的最佳化石记录。我建议继续我的基于系统发育的研究，通过二叠纪-三叠纪边界对上述羊膜类群的生存进行研究。根据最近的一项建议，我将扩大我的计划，看看卡鲁地区的羊膜动物在灭绝后的生存情况，“幸存的动物群”屈服于二叠纪-三叠纪边界主要灭绝之后的第二次灭绝。研究结果将有助于阐明二叠纪-三叠纪灭绝对四足动物的影响与对植物和海洋无脊椎动物的影响的差异，植物和海洋无脊椎动物经历了一次灭绝脉冲，随后经历了4-5万年的恢复期。

Of the five known mass extinction events, the Permo-Triassic extinction event is regarded unanimously as the most severe in Earth history. The consensus view has been that 70-90% of species became extinct 251 million years ago. Such estimates of high species mortality were based on ranks-based studies of low taxonomic resolution (family-level groups). My own investigations, using phylogenetic studies of higher resolution (species and genera), suggest that terrestrial vertebrates (tetrapods) experienced low extinction pressure during the Permo-Triassic extinction event.     To date I have examined the Permo-Triassic boundary survivorship of amniotes (mammals, reptiles, birds, and their fossil relatives). The two reptile groups examined, procolophonoid parareptiles and archosauromorph diapsids, exhibit roughly 29% and 14-17% extinction, respectively. Current work on therocephalians, a group of synapsid amniotes, suggests that they experienced 43% extinction. Judging from published phylogenies, cynodont synapsids suffered 40-50% extinction. The evidence so far suggests that the amniote extinctions were not as severe as commonly believed, and that the effects of extinction were not even handed among the groups.     Procolophonoids and therocephalians are the most diverse and, after lystrosaurids, the most commonly encountered amniotes in the Karoo Basin of South Africa, the country with the best fossil record for studying the effect of this extinction event on tetrapods. I propose to continue my phylogenetically-based research on the survivorship of the above mentioned amniote groups through the Permo-Triassic boundary. I will expand my program by looking at the post-extinction survivorship of amniotes in the Karoo, in light of a recent suggestion that a "survivor fauna" succumbed to a second pulse of extinctions that followed the main extinctions at the Permo-Triassic boundary. The results of the study will help to elucidate the differences of effect of the Permo-Triassic extinctions on tetrapods with respect to that on plants and marine invertebrates, which experienced a single extinction pulse followed by a recovery period of 4-5 million years.