Taxonomy Of Subfamily Aphodiinae In Myanmar Ambers And Taxonomic Assessment Of Extant Morphological Characteristics

The subfamily Aphodiinae belongs to Coleoptera,Scarabaeidae.The known species with 14 tribes,about 380 genera and more than 3,500 species,which are widely distributed in the world.With the discovery of new species of Aphodiinae,it is particularly critical to use effective identification characteristics.However,the morphological convergence of Aphodiinae leads to an inefficient and controversial classification of Aphodiinae by using traditional taxonomic methods.In addition,the research of Aphodiinae fossils is less and mainly concentrated on Paleogene,and the classification and evolution of Aphodiinae groups are slow due to the indistinguishability of morphology and intermittent fossil records.In this paper,nine specimens of Aphodiinae in the early Late Cretaceous Myanmar amber were described,they are belonged to nine different genera.The morphological characters of the pronotum and elytra of extant and extinct Aphodiinae are extracted,and the differences of them were analysed by Principal Component Analysis(PCA),Canonical Variable Analysis(CVA)and Discriminant Function Analysis(DFA)using geometric morphological methods to evaluate the morphological similarity between ancient and extant Aphodiinae.By using this method to extracted the morphological information of the pronotum,elytra,epipharynx and aedeagus of the extant Aphodiinae,the significant morphology differences of these features in tribe and genus levels were screened,and the taxonomic significance of the morphological information contained in the test features was clarified.In addition,this study combines cladistic systematics and geometric morphology methods to reconstruct the ancestral morphology of the five morphological characters of Aphodiinae,laying a foundation for exploring the morphological evolution of Aphodiinae.In this study,the specimens of all genera and species were described in detail,the overall and partial detailed feature map were provided,and their overall and important local features were drawn respectively.Based on the geometric morphological analysis of pronotum and elytra of the ancient and extant Aphodiinae,the results show that the fossil Aphodiinae and most extant Aphodiini overlap and cannot be clearly distinguished;DFA analysis showed that within fossils,there are two groups identified as based pronotum and one group based on elytra,and the other is identified as Lomanoxiini according to the elytra morphology,there is no obvious intersection about Corythoderini,Odontolochini and Rhyparini.This study proves that some fossil groups of Aphodiinae have some morphological similarities with the pronotum and elytra of the extant Aphodiinae,but it needs to be classified and identified with other characteristics.Based on the morphology of pronotum,elytra,epipharynx and the lateral and dorsal views of the aedeagus,the Geometric Morphological Analysis was carried out.It was found that the morphological differences between the groups were mainly concentrated in the anterior horn,the posterior horn and the side margins of the pronotum;the anterior and lateral margins of the elytra;the anterior area of the epipharynx,the lateral margin of the epitorma;the chaetoparia;the phallobase and endoparamere of the aedeagus could regard as the continuous characters of the morphological variation of the Aphodiinae.The results of CVA showed that the significant proportions of the shape variation represented by the pronotum,elytra,epipharynx and lateral and dorsal views of aedeagus at tribal level were over 70%.It is proved that there are significant differences in pronotum,elytra,epipharynx,lateral and dorsal views of aedeagus among the Aphodiinae.The results of DF A showed that the correct discrimination rates of the pronotum,elytra,epipharynx,the lateral view of aedeagus and dorsal view of aedeagus reached to 53.8%,81.9%,97.9%,93.4%and 87.5%respectively at tribal level,and the correct discrimination rates reached 89.5%,89.7%,98.4%,94.0%and 81.5%respectively at genus level.It means that there were more important to refer to the morphological characteristics of epipharynx,the lateral and dorsal views of aedeagus in classifying and identifying Aphodiinae.At the same time,the ancestral morphology of five morphological characteristics was reconstructed.The evolution trend of the pronotum showed that the anterior horn was depressed from inward to significantly contracted,the posterior horn was expanded from outward to significantly contracted,and the whole was trapezoidal.The anterior margin of the elytra is gentle to protrude outward,the laterior margin is elongated longitudinally,and the posterior margin is bent outward;The base of the epitorma of the epipharyx is enlarged,the lateral margin is flat to wide,and the middle of the anterior margin protrudes from the anterior area of the corypha or the sockets of the coryphal celtes;In the lateral view of aedeagus,the end of the paramera is flat until it is obviously folded back and bent inward,and the length of the lateral process of the paramera and the tegmen changes;In the dorsal view of aedeagus,the tegmen outward from nearly flat until it is uniform,and the length of the paramera and the tegmen changes;The above effectively inferred the possible evolution trend,providing evidence for exploring the morphological evolution of Aphodiinae and related research.This research confirmed the morphological similarity between ancient and extant Aphodiinae.At the same time,it revealed that the morphological differences between the epipharynx and aedeagus were better than those of the pronotum and elytra at different tribal and genus level,which provided a reference for the classification and identification of the higher taxa of Aphodiinae.