The fossil record contains vital information about the evolution of lineages and is a source of data that cannot be reconciled in any other way than by the direct observation of morphologies. Total-evidence phylogenetic reconstruction is being increasingly used to assess the position of extinct taxa by incorporating morphological data from extinct and extant taxa together with molecular data from extant taxa in a united framework. Here we apply the method to two Cretaceous Burmese amber inclusions belonging to the rove beetle subfamily Paederinae. To perform the total evidence analysis, we constructed the first morphological matrix and the most comprehensive molecular dataset for the subfamily. Our analyses reveal an extinct lineage of Paederinae rove beetles with a suite of unique morphological characters, resulting in the description of a new genus: Diminudon gen. nov. and two new species: D. schomannae sp. nov. and D. kachinensis sp. nov. Simultaneously our analyses provide new insights into the evolution and classification of the entire subfamily. We also discuss the unusually small size of the newly described Paederinae, which may represent an additional case for miniaturization in the Cretaceous.