Ordovician sponge spicules from Spitsbergen, Nevada and Newfoundland: new evidence for hexactinellid and demosponge early diversification

Abstract

Unusually well-preserved spicule assemblages from three Lower to Middle Ordovician localities are examined: Spitsbergen (Floian-Dapingian), Nevada (Vinini Formation, Dapingian) and Newfoundland (Cow Head Group, Tremadocian-lower Darriwilian, and Table Head Group, mid-Darriwilian). The recorded diversity increases the knowledge of sponge spicules in the Lower Ordovician and their palaeogeographical distribution. Hexaster type microscleres and scopules, equinate hexactins, pinular hexactins and inflated pentactins and hexactins are the main spicule types amongst the Hexactinellida. Hemidiscs and a possible amphidisc are recorded and can be evidence of the presence of the hexactinellid subclass Amphidiscophora. Oxyasters, C-shaped sigmata and trianes are the main spicule types amongst demosponges. The presence of sigmata and oxyasters can also be evidence of the presence of two main orders of extant demospongids: Sigmatophora (now Spirophorida) and Astrophora. One modified octactinellid spicule type is found from Calcarea. The presence of echinate and pinulate hexactins amongst megascleres suggests a protective functional morphology. These features can be associated with an evolutionary tendency which is seen mainly amongst hexactinellids and demosponges for an efficient occupation of shallower settings and/or a defensive armoury strategy. A newly recorded flat-top pinulate form is also a suitable element for reinforcement or protection of any external surface. Some of the microscleres found can be considered ancient homologues of recent hexasters, sceptrules, hemi/amphidiscs and oxyasters. This work suggests that the microscleres of hexactinellid and demosponge subclasses were already present and significantly diversified in the Early Ordovician. The presence of definite axial canals in scopules provides key evidence for this statement. This finding is significant and confirms the presence of the Sceptrulophora in the early Palaeozoic. The microscleres comes from widely separated Lower Ordovician localities and possess similar forms to those found in Mesozoic microscleres, implying a conservative morphology.

An outline of the distribution and diversity of Porifera in the Ordovician Builth Inlier (Wales, UK)

“…There is also a greater range of spicule modifications present in shallow-water species. A similar pattern was observed by Carrera and Maletz (2014) in their study of assemblages of isolated Ordovician spicules, and this appears to be a global trend among at least hexactine-bearing groups, with the most conservative spicule morphologies occurring in species from offshore habitats.…”

Sponge spicules from the Holm Dal Formation (Cambrian Series 3, Guzhangian) of North Greenland (Laurentia)

“…-In terms of the large number of radiating rays, Seqineqia resembles Kometia Webby & Trotter, 1993 but the numerous secondary rays in the latter arise by subdivision of one axial ray. The underlying hexactin symmetry of Kometia is clearly evident, with well developed paratangential rays and the modified axial ray (Webby & Trotter 1993;Mehl 1998;Won et al 2007;Carrera & Maletz 2014). In Seqineqia all rays are preserved within a single plane without differentiation of an axial ray.…”

Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record

“…The majority of fossil sponge studies concerns bodily (entirely) preserved sponges while loose sponge spicules were a much less common object of investigations, and in most cases these studies do not proceed further than the description of spicule morphotypes (see Rigby et al 2001 and the literature cited therein). However, diversified assemblages of disassociated sponge spicules are known already from the Cambrian (see Castellani et al 2012 and reference therein) and were described several times from the Paleozoic (e.g., Mostler and Mosleh-Yazdi 1976;Mehl 1998;Debrenne and Reitner 2001;and Carrera & Maletz 2014) and Mesosoic (Rauff 1893-95;Mostler 1971Mostler , 1972Mostler , 1976Mostler , 1986. The Tertiary record of loose sponge spicules is less studied (e.g., Etheridge 1888;Card & Dun 1897;De Laubenfels 1953;Picket 1983;Wiedenmayer 1994;Pisera & Hladilová 2003;Pisera et al 2006;and Łukowiak et al 2014).…”