On The Systematic Palaeontology And Development Of Family Leanchoiliidae Fossil Arthropods From The Chengjiang Biota

The early Cambrian Chengjiang biota from the eastern Yunnan,China is a celebrated fossil Konservat-Largestatte that is well-known for the preservation of the soft-bodied fossils.The Arthropoda fossils represent the most diverse group in the Chengjiang biota,with the species number being 30.8% of the 250-known species.With the preserved soft tissues and structure,these arthropod fossils have playing a key role in understanding the origin and early evolution of living euarthropod,the most diverse animal group ever lived on the earth.Family Leanchoiliidae is one of the most abundant representatives of Chengjiang arthropods,with its only known species,Leanchoilia illecebrosa,being the dominant species of Chengjiang.This thesis aims to investigate this fascinate fossil treastures of Leanchoiliidae from the Chengjiang biota,with specifical focuses on its morphology,systematics,phylogeny and development.An exhaustive investigation over ten thousands specimens and morphological description revealed several new morphologic types in addition to Leanchoilia illecebrosa,which were identified respectively as Leanchoilia obesa sp.nov.,Alalcomenaeus siveterorum sp.nov.and Alalcomenaeus caudellus sp.nov.Based on further revision of all other known species in Leanchoiliiidae,a revised diagnosis of the family was present: megacheiran bearing a great appendage with five podomeres;proximal two podomeres short,forming a peduncle of great appendage;distal three podomeres bearing flagellam,with first and second one bearing a long endites,third distal podomere extremlly long,bearing claws in addition to flagellum.Trunk consisiting of 11 body segments;telson fringed with setae.A cladistic analysis on all 5 genera,13 species of Leanchoiliidae,together with other 7 megacherians is conducted.The monophyly of Family Leanchoiliidae was confirmed,but Order Leanchoiliida is revealed as a polyphyletic group.Whithin Leanchoiliidae,the monophyly of genus Leanchoilia is not supported,but several well-known species grouped together as a core of Leanchoilia,which includes Leanchoilia superlata,L.illecebrosa,L.obesa,L.persephone and probally L.robosoni.The result further revealed that genera Actaeus,Oestokerkus and Yauunik were nested within ‘pan-Leanchoilia'.It is suggested that revision on these three genera is the key problem in the systematic of Leanchoiliidae.A biparted model of the telson in Leanchoiliidae is suggested,which is supported by the differentiated development of the anteiro setae-less base and the posterior setae-bearing triangular region in the telson of Leanchoilia obesa.This indicates that telson is an important morphological resource in the classification of Leanchoiliidae.Quantitative analyses were conducted for the first time to investigate the development processes of Leanchoilia illecebrosa and Alalcomenaeus siveterorum.The result indicates that,in both taxa,the length of the body(from the anterior of head shield to the end of the telson)growed more quickly than the width,indicating a body narrowing trend during the development.Such a trend is interpreted as a reason accounting for the niche differenciation between juveniles and adults in Leanchoiliidae.The result further reveals that the trunk,the head shield and the telson have different growth rates,which suggests that the differentiation in the growth rates of different body parts might account for the diversification of Leanchoiliidae in the early Cambian,as all these body parts,their length,width and other respectives have been used in distinguishing species and genera within Family Leanchoiliidae.