Update on the northern Australian Cambrian spongesRankenella, JawonyaandWagima

Abstract

New material from the Ordian to early Templetonian (early Middle Cambrian) of the Georgina Basin and Daly Basin in northern Australia allows further observations on the anthaspidellid sponge Rankenella mors and the chambered heteractinide sponge Jawonya gurumal respectively. Explanate specimens of R. mors are found to bear closely spaced, rimmed oscules, and the known range of the species is extended from the Ranken Limestone near Soudan to include the Arthur Creek Formation near Ammaroo. Jawonya gurumal from the Tindall Limestone near Claravale is better preserved than type and topotype material, and demonstrates that the genus is two-walled, and not one-walled as originally described. Furthermore, exopore architecture is much more complex than previously envisaged. The co-occurring related genus Wagima is also considered to be two-walled. Rankenella in the Ranken Limestone flourished in a low-energy, shallow subtidal marine environment subject to episodic higher-energy events that generated ooid shoals and flat-pebble conglomerates. In the Arthur Creek Formation the genus occurs in anaerobic calcimudstone deposited in a low-energy shelf area of limited circulation. Jawonya and Wagima are elements of a spongemollusc association in open shelf onkoid limestones of the Tindall Limestone. Rankenella is among the oldest known intact demosponges. Spiculation in Jawonya and Wagima suggests that the history of the heteractinide astraeospongiid-wewokellid lineage was one of Ordovician reduction or loss of original polyactines in favour of octactines, followed by polyactine reinstatement in the Carboniferous.