Strepsiptera were once believed to be the sister group to the beetle families Meloidae and Ripiphoridae, which have similar parasitic development and forewing reduction; early molecular research suggested their inclusion as a sister group to the flies, in a clade called the halteria, which have one pair of the wings modified into halteres, and failed to support their relationship to the beetles. Further molecular studies, however, suggested they are outside the clade Mecopterida (containing the Diptera and Lepidoptera), but found no strong evidence for affinity with any other extant group. Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction. The most basal strepsipteran is the fossil "Protoxenos janzeni" discovered in Baltic amber, while the most basal living strepsipteran is "Bahiaxenos relictus", the sole member of the family Bahiaxenidae. The earliest known strepsipteran fossils are those of "Cretostylops engeli", "Kinzelbachilla ellenbergeri", "Phthanoxenos nervosus" and "Heterobathmilla kakopoios," discovered in middle Cretaceous Burmese amber from Myanmar.