Idanoceras, a new heteromorph ammonite genus from the Late Albian of eastern Australia

Abstract

The late Albian marine fossil record from eastern Australia derives from the sedimentary succession of the Great Artesian Basin deposited in a vast epicontinental sea which then covered much of the continent (see Frakes et al., 1987). Ammonites of this age are common but their generic diversity is low. Heteromorph assemblages almost exclusively comprise the taxa Myloceras, Labeceras sensu stricto and Labeceras (Appurdiceras) of the Family Labeceratidae that were widely distributed in higher latitudes of the Southern Hemisphere during Late Albian time (see Aguirre Urreta and Riccardi, 1988; Klinger, 1989). Some 19 endemic species of these genera are recorded from the Great Artesian Basin in the present literature (Etheridge, 1892; Whitehouse, 1926; Reyment, 1964) and there are additional undescribed species (Henderson and McKenzie, unpublished data). The Australian Late Albian epicontinental sea was clearly a site of significant speciation for Labeceras and Myloceras and it has been argued that the Great Artesian Basin represents the evolutionary center for these genera (Henderson, 1990).