The Evolution And Divergence Of Late Mesozoic Cockroaches As Indicated By Myanmar Amber

Cockroaches are one of the insect groups that left numerous fossils,with the most ancient ones dating back to the Carboniferous.Most of the genera and species of the fossils are known from forewing only,they are not only taxonomically dubious,and virtually fail to reveal the evolution of cockroaches.Despite some published fossils that are almost completely preserved,the evolutionary history of cockroaches is poorly known,especially the origin and evolution of extant cockroaches and their major clades.The Cretaceous Myanmar amber preserves numerous,various cockroaches,with observable fine structures.The classification and identification of cockroaches depend considerably on fine structures.Hence,Myanmar amber provides unprecedentedly vast amount of information,opening a window into the evolution of cockroaches.The present study assessed and revised the taxonomic system of fossil cockroaches,and accordingly described important representatives of cockroaches preserved in Myanmar amber,and discussed the evolution and divergence of late Mesozoic cockroaches.This study reviewed the research history of major taxonomic groups of cockroaches.The vernacular name "cockroach" and corresponding scientific names are considerably ambiguous.In order to define the scope of this study,and to clearly refer to the organisms in question,the present study follows previous practice to delimit cockroaches into the following groups with defined scientific names:Holopandictyoptera(all cockroaches and non-roach descendants),Eoblattodea(cockroaches with Ensifera-type ovipositor),Dictyoptera(cockroaches with Mantodea-type ovipositor and all descendants),Blattodea(cockroaches with extant cockroach type ovipositor and all non-roach descendants)and Blattaria(cockroaches with extant cockroach type ovipositor).This study assessed the value of forewing venation of extant cockroaches in taxonomy and phylogenetics,and concluded that the forewing-venation-based taxonomic system is unreliable,particularly the familial group taxa that were established on forewings without autapomorphies or without unique character set.This study described 36 cockroach specimens and one dictyopteran ootheca preserved in Myanmar amber,of which Manipulator modificaputis Vrsansky&Bechly,2015 and Huablattula hui Qiu et al.,2019 were complemented,the following taxa were discovered:Nodosigalea Li&Huang,2018,Nodosigalea burmanica Li&Huang,2018,Crenocticola Li&Huang,2019,Crenocticola burmanica Li&Huang,2019,Manipulatoides gen.nov.,Manipulatoides obscura gen.&sp.nov.,Cercoula Li&Huang,2021,Cercoula brachyptera Li&Huang,2021,Triloblatta gen.nov.,Triloblatta unicolor gen.&sp.nov.,Ensiferoblattidae fam.nov.,Ensiferoblatta gen.nov.,Ensiferoblatta oecanthoides gen.&sp.nov.,Proceroblatta gen.nov.and Proceroblatta colossea gen.&sp.nov..In addition,Crenocticola svadba Podstrelena,2020 is synonymized with Crenocticola burmanica.Nodosigalea burmanica is the earliest fossil of Corydiinae ever known.Crenocticola burmanica is the earliest fossil of Nocticolidae ever known.Cercoula brachyptera is the first brachypterous roach fossil.Ensiferoblatta oecanthoides and Proceroblatta colossea are the latest fossil of Eoblattodea ever known.The most significant is that Triloblatta unicolor supports corydioid origin of termites over blattoid origin.This accords with a previous morphological phylogeny but challenges DNA phylogenies of recent studies and this study.With the help of published DNA data,the present study performed Bayesian phylogenetic inference and divergence time estimates.Both of the fossils and molecular results suggest that three superfamilies of extant cockroaches originated in late Jurassic or around the J-K boundary.Many coeval cockroaches became extinct,including the "agile type" represented by Manipulatoridae,and the "hard-shell type"represented by Umenocoleidae.The major contributing factor to their extinction might be the life habit that they were exposed to external environment.In contrast,"traditional type" cockroaches survive to present,this may be due to their broad food sources and life habit that they tend to hide in crevices and burrows.In addition,this study did not find any evidence for the previous hypothesis that "agile type"cockroaches are obligate predators.The extinction of Eoblattodea might be related to the extinction of certain gymnosperm host,of which the niche was replaced by angiosperm.