Search

The unusual findings of Lower and Middle Ordovician tiny sclerite-type elements in the San Juan Formation of the Argentine Precordillera are described and analysed. The well-preserved silicified and phosphatized association consists of spindle-shaped morphotypes, ornamented with small regular granules or tubercles with some elements connected by their tips in a linear manner. Some morphologic characteristics of these mostly fused or connected sclerite-type elements are present in the alcyonacean octocorals. Their affinities with sponge spicules are also discussed. The oldest records of alcyonacean sclerites have been dated as late Llandovery to late Wenlock (Silurian). The discovery of possible octocoral skeletal elements in the Lower Ordovician of western Argentina may represent the oldest occurrence of such fundamental skeletal elements in the evolutionary history of the octocorals. Although a proper group assignment is still speculative at this state of knowledge, there is an implication that these early forms could be axial skeletal elements comparable to those seen in the Scleraxonia or Calcaxonia octocorals. One new genus Catenatus and new species Catenatus argentinus are described. [ABSTRACT FROM AUTHOR]

A Mississippian hexactinellid sponge from the western Argentina improves the extremely poor late Paleozoic sponge records from Gondwana. The sponge is included in the subfamily Thysanodictyinae of family Dictyospongiidae. The new genus and species Minitaspongia parvis is erected, and its well-preserved spicular structure is described in detail representing the first approximation of the spicule assemblage in Thysanodictyinae. The skeleton is clathrate, three-dimensional with at least two ranks of rectangular openings. This first report of this subfamily outside North America represents the best-known hexactinellid and the first dictyosponge record from the Carboniferous of Gondwana. Unlike the occurrences of Thysanodictyinae in North America, with thick skeletons linked to high-energy shallow water settings, Minitaspongia occurs in low-energy water siliciclastic settings related to a cold climate and glacimarine deposits. Accordingly, the complex wall structure of this sponge should not be invoked as a necessary adaptation to high energy and shallow water settings. [ABSTRACT FROM AUTHOR]