Taxonomy And Morphology Of The Subfamily Zigrasimeciinae(Hym-Enoptera) In Mid-cretaceous Amber

The ants(Hymenoptera: Formicidae)are the most iconic social insects.The oldest fossil ants are known from the Cretaceous,approximately 100 Ma.At that time,the ecological landscape of the Formicidae was already diverse.Kachin amber(Myanmar),which formed around 99 Ma,is the most representative of the exceptionally well-preserved biota and the ant taxa within it have received widespread attention.As one of the oldest ant fossils,the study of ancient ants in Kachin amber is important for understanding early Formicidae diversity,the early social evolution of ants,and other significant scientific questions.In this research,391 pieces of Kachin amber from the Yunnan Provincial Key Laboratory of Palaeontological Research,Institute of Palaeontology,Yunnan University,were studied in detail with the aid of an ultra-deep field microscope imaging technique,and 58 specimens of Formicidae were selected from the collection.Through taxonomic and morphological identification,and judging from known ancient ant genera,eight specimens of the family ?Zigrasimeciinae(subfamily,of which seven are ?Zigrasimecia and one is ?Protozigrasimecia)were identified.These specimens were studied to determine the taxonomic position of each specimen within the subfamily ?Zigrasimeciinae,and three new species were discovered(Zigrasimecia goldingot Zhuang et al.,2021,Zigrasimecia zui sp.nov.and Zigrasimecia wilsoni sp.nov.).In addition,based on these taxonomic and external morphological studies,computed tomography scanning,computer 3D modelling,and virtual dissection of some specimens were carried out,resulting in the discovery and description of the most complete and oldest known internal anatomy of ants.Through comparison with living ants,the study identifies the nervous,digestive,muscular,and exocrine systems of the ancient ants.This study provides key organ evidence of the early social evolution of the ant and fills a gap in the previous description of the predatory behaviours of the ?Zigrasimeciinae,while also revealing the specificity and scientific potential of amber for the preservation of arthropod soft tissue organs.