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An unusual Upper Cretaceous (Santonian) hexactinellid sponge from the Great Valley sequence, western Sacramento Valley, Northern California
Published online by Cambridge University Press: 20 May 2016
Abstract
The new farreid hexactinellid sponge Hormathospongia dictyota new genus and new species, is described from the upper Santonian Dobbins Shale Member of the Forbes Formation of the Upper Cretaceous Great Valley Sequence from the west side of the Sacramento Valley, northwest of Sacramento. The relatively simple skeleton is composed of quadrangularly arranged hexactines with overlapping rays, an arrangement strikingly similar to the skeletal structure of early Paleozoic reticulosid hexactinellids. However, the California Cretaceous sponges clearly show those spicules embedded in siliceous beams that are united to form a solid dictyonal skeletal framework of only a single layer of regular mesh. Such an occurrence and stratigraphic relationships suggests that the dictyonine sponges had their origin from the simply spiculed reticulosid hexactinellids rather than from the more complex dictyosponges.
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