Queensland Middle Cambrian Bradoriida (Crustacea): new taxa, palaeobiogeography and biological affinities
Title:
Queensland Middle Cambrian Bradoriida (Crustacea): new taxa, palaeobiogeography and biological affinities
Author:
Jones, P. J. McKenzie, K. G.
Appeared in:
Alcheringa
Paging:
Volume 4 (1980) nr. 3 pages 203-225
Year:
1980
Contents:
Two new genera of phosphatic bradoriids are described from the insoluble residues of Middle Cambrian limestones from two sites in the Georgina Basin: Flemingia gen. nov. from south of Duchess in the late Templetonian Triplagnostus gibbus Zone in the Monastery Creek Phosphorite Member of the Beetle Creek Formation; and Oepikaluta gen. nov. from northwest of Mount Isa in the Thorntonia area in the upper (Undillan) part of the Currant Bush Limestone. The Templetonian bradoriids include five species previously described and named by Fleming (1973), the new taxa Flemingia duo gen. et sp. nov. and Dielymella? dubia sp. nov., and unnamed species belonging to Svealuta Opik 1961 and possibly Aristaluta Opik 1961. They appear to be part of the biocoenosis of the quiet inner margins of an ancient Bahama Banks type environment. Two new families are proposed within the suborder Phosphatocopina Muller 1964 — Oepikalutidae for Zepaera Fleming and the new genera Oepikaluta and Flemingia, and Monasteriidae for Monasterium Fleming — and the diagnosis for the Templetonian species Zepaera rete Fleming 1973 is emended. The trace of four thoracic segments in the new Undillan species Oepikaluta dissuta gen. et sp. nov. is consistent with the hypothesis of the presence of four thoracic limb pairs in the ancestral ostracode. Palaeobiogeographically, the Australian bradoriids conformed to a global pattern of establishment, rapid diversification into new lines once stocks became established, and almost equally rapid extinction of all except conservative elements of the new taxa. Carapace features are evaluated, and we conclude that Bradoriida, as currently understood, are probably polyphyletic. Thus, while the affinities of many taxa lie clearly with ostracodes, others may be more closely related to phyllocarid-like and branchiopod-like crustaceans. That three groups which are distinct today had Cambrian ancestors which were convergent in an important feature — the carapace — is consistent with the primitive nature of the caridoid grade of crustacean evolution, and can be considered supportive of a monophyletic origin for the Phylum Crustacea.
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