A review of the taxonomy and systematics of the echinoid genus Monostychia Laube, 1869

摘要

A review of Monostychia, a stratigraphically important clypeasteroid echinoid genus in southern Australian Oligocene/Miocene strata, reveals uncertainty in relation to morphological features used in taxonomy. The result is that the exact systematic position of the genus remains unresolved at subfamily level. Monostychia and its type species, M. australis, are redescribed. Monostychia australis is restricted to the lower to middle Miocene Glenforslan Formation of the Murray Basin. Three other species currently within Monostychia, M. etheridgei, M. loveni and M. elongata, are discussed. Although it is concluded that M. etheridgei belongs in the genus and is a distinct species, the taxonomic position of M. loveni is questioned, and the validity of M. elongata as a separate species from M. australis remains uncertain. This work lays the foundation for further revisions of Monostychia with an expectation that such work will provide the basis for character determination that may be useful across other echinoid taxa.