see text The grass warblers are small passerine birds belonging to the genus Locustella.

Formerly placed in the paraphyletic "Old World warbler" assemblage, they are now considered the northernmost representatives of a largely Gondwanan family, the Locustellidae.

A molecular phylogenetic study of the grassbird family Locustellidae published in 2018 found that the genus Locustella consisted of two distinct clades.

[7][6] A fossil acrocoracoid from the Late Miocene (about 11 mya) of Rudabánya (NE Hungary) is quite similar to this bone in the present genus.

[8] Given its rather early age (most Passerida genera are not known until the Pliocene), it is not too certain that it is correctly placed here, but it is highly likely to belong to the Locustellidae, or the Sylvioidea at the least.