<p>Endomychidae is a moderately diverse family of mycetophagous beetles. However, our knowledge about their macroevolution remains insufficient. In this study, we describe <i>Cretostenotarsus elongatus</i> sp. nov. from the mid-Cretaceous (Cenomanian, ca. 99&#xa0;Ma) Kachin amber, representing the second record of ‘Higher Endomychidae’ from the Mesozoic. The relatively low taxonomic and morphological diversity suggests that major diversification of 'Higher Endomychidae' had not yet occurred by the mid-Cretaceous. Furthermore, we investigated the diversity dynamics of Endomychidae during the Meso-Cenozoic. The biodiversity analyses reveal a higher taxonomic diversity of Endomychidae in the Cenozoic than that in the Mesozoic, indicating a diversification during the Meso-Cenozoic. A comparison of the diversity composition among fossil assemblages and extant fauna reveals that the percentage of ‘Higher Endomychidae’ has largely increased over time. Our estimation of diversification rate indicates that ‘Higher Endomychidae’ steadily diversified since the mid-Cretaceous, while the net diversity-through-time curve is much flatter in basal endomychids, with a sharp rise around 51–53 Mya, which is congruent with the diversification of ants, suggesting that myrmecophily may provide a new niche for the resurgence of basal endomychids. Despite the unclear underlying mechanism, we assumed that the evolution of diverse defensive strategies may have facilitated the evolutionary success of ‘Higher Endomychidae’. The present study provides a preliminary picture of the macroevolution of Endomychidae. Further research is needed to unravel the evolutionary biology of this group.</p>