Lives morphologies and body development of Cambrian nemathelminths and arthropods, a testtool for phylogeny analyses and hypotheses

点击翻译按钮获取中文摘要

There are four major sources of exquisitely preserved early representatives of various metazoan taxa: the Lower Cambrian Chengjiang Lagerstätten, the Lower Cambrian Sirius Passet Lagerstätte, the Middle Cambrian Burgess Shale Lagerstätten and the Lower to Upper Cambrian ¿Orsten¿ Lagerstätten. The fossils of these Lagerstätten have contributed significantly to our knowledge of early metazoan evolution and the morphologies and life styles developed at the time, when metazoan life began to radiate. Many questions have become satisfactorily resolved, but one of the major questions remained: Where do the arthropods, the largest animal taxon belong to systematically? Which is the closest relative? Seven years ago, the long-standing dogma of a sister-group relationship with annelids was questioned and the new idea of a nemathelminth-arthropod relationship put forward. Still today, this is not resolved. Focusing on representatives of nemathelminths and arthropods from the fossil lagerstätten mentioned above, we will investigate original material with particular emphasis on structural and functional design and body development. This includes the important and most critical aspects of segment evolution, the external expression of internal serial mesoderm subdivision, body tagmatisation, and appendage formation, features partly most likely primary absent in nemathelminths. Our particular aim is to present the data accumulated from these lived morphologies as a test tool for phylogeny hypotheses resulting from the different other work groups within the Priority Programme.