A new genus and species of fossil Eumastacoidea Burr, 1899 from Kachin amber is described. Burmeumastax lexiaegen. et sp. nov. is the 14th member of this superfamily known from fossil material and only the third to predate the Cretaceous-Paleogene (K-Pg) extinction event, following Archaeomastax jurassicus Sharov, 1968 and Taphacris turgis Lin, 1980. Most fossil species of Eumastacoidea were reported based mainly on wings, with B. lexiae being only the second species with most parts of the body well preserved, predating the only other species in this condition by ca. 80 Myr. Burmeumastax lexiae is brachypterous with a body morphology similar to extant species of apterous Eumastacoidea. However, its last abdominal tergite consists of seven separate plates, whereas this structure is made up of only one or two plates in modern-day species. Because Eumastacoidea taxonomy based on morphology relies heavily on internal genital structures, the position of B. lexiae within the Eumastacoidea is uncertain. Since the orthopteran fauna of the Burma Terrane appears to be influenced by South American-Gondwana (based on the high diversity of Tridactyloidea Brullé, 1835 and the Elcanidae Handlirsch, 1906 found in Burmese amber compared to deposits of the Crato-Formation from Brazil), it is speculated that B. lexiae may belong to Eumastacidae Burr, 1899, as this is the only family of Eumastacoidea with a wide distribution across South America. The new species provides remarkable insights into the early evolution of Eumastacoidea and further highlights the insect diversity of the Burma Terrane.
