Tackling taxonomic and taphonomic biases in the Triassic fossil fish record

鳐鱼（放射线鳍类）是当今最多样化和最成功的脊椎动物群体，占现存脊椎动物物种的一半以上。在它们近5亿年的历史中，它们经历了无数次的大灭绝，但与许多其他物种相比，人们对这些毁灭性的大灭绝事件对它们进化的影响的了解有限。尽管在世界各地的早三叠纪沉积物中发现了数千块保存完好的二维和三维化石，但人们对二叠纪-三叠纪大灭绝（2.52亿年前）如何影响鳍状鱼类的了解尤其少。造成这种情况的原因有两个方面：对早三叠纪鳐鳍的分类和关系没有强有力的假设，以及对可能对早三叠纪鱼类化石记录产生偏见的地面学过程的理解有限。这个项目将结合CT扫描、系统发育分析和语音学调查来解决这些偏见。最近的工作已经建立了早期放光翼目动物之间关系的主干，学生将使用传统描述方法和CT扫描相结合的方法将关键的三叠纪早期分类群置于这个系统发育框架中，并回答分类问题。我们对鱼类的分类学和腐烂的理解大多是基于硬骨鱼，它表现出与早期放光鳍鱼非常不同的形态，特别是在鳞片组织学方面。不同类型的鳞化可能对不同鱼类种群的保存潜力产生深远的影响，可能会影响地球历史上这一关键时期的化石记录，并扭曲我们对二叠纪-三叠纪大灭绝后鳐鱼恢复的理解。该学生将通过对有鳞和无鳞的分类群进行有针对性的调查，以及对现存有鳞的放线菌进行分类调查，来研究这种方法的影响。这项研究将为鳐鱼的埋藏学过程和不同鱼类化石群体的不同保存潜力提供新的见解。它还将有助于修订放光翼类关系的假设，回答有关二叠纪-三叠纪大灭绝对最大的现存脊椎动物进化的影响的基本问题。

Ray-finned fishes (actinopterygians) are the most diverse and successful group of vertebrates today, accounting for over half of living vertebrate species. In their nearly half-a-billion-year history they have survived countless mass extinctions, but, in contrast to many other groups, there is limited understanding of the effect of these devastating mass extinction events on their evolution. Despite thousands of exceptionally preserved two- and three-dimensional fossils from early Triassic deposits worldwide, there is a particularly poor understanding of how the Permo-Triassic Mass Extinction (252 million years ago) impacted ray-finned fishes. The reasons for this are two-fold: no robust hypothesis of the taxonomy and relationships of early Triassic ray-fins, and limited comprehension of the taphonomic processes that may have biased the Early Triassic fossil fish record. This project will combine CT scanning, phylogenetic analyses and taphonomic investigations to tackle these biases. Recent work has established a backbone of relationships amongst early actinopterygians, and the student will use a combination of traditional descriptive methods and CT scanning to place key early Triassic taxa into this phylogenetic framework and answer taxonomic questions. Much of our understanding of fish taphonomy and decay is based on teleost fishes, which display a very different morphology from early actinopterygians, in particular with regard to scale histology. Different types of squamation may have a profound impact on the preservation potential of different fish groups, potentially biasing the fossil record in this key period of earth's history and skewing our understanding of ray-finned fish recovery after the Permo-Triassic mass extinction. The student will investigate the effects of this through targeted interrogation of scale-bearing and scaleless taxa as well as taphonomic investigation of extant scale-bearing actinopterygians. This research will provide new insights into taphonomic processes acting on ray-finned fishes and the varying preservation potential of different fossil fish groups. It will also contribute to a revised hypothesis of actinopterygian relationships, answering fundamental questions concerning the impact of the Permo-Triassic mass extinction on the evolution of the largest living vertebrate clade.