Vauxiids as descendants of archaeocyaths: a hypothesis

Abstract

Archaeocyaths were one of the major animal groups contributing to the Cambrian Explosion. Despite an overall poriferan appearance of their hypercalcified skeletons, they exhibit a number of peculiar features such as the presence of septa and an absence of spicules. This sets archaeocyaths apart from general trends in early poriferan evolution. Fossils recently discovered from the early Cambrian Guanshan Lagerstätte of South China exhibit features typical for the suborder Archaeocyathina whilst possessing a silicified skeleton associated with carbonaceous material. This rigid fibrous skeletal framework, on the other hand, fits the diagnosis of the supposed ancestral aspiculate demosponges, the family Vauxiidae. By a detailed description of this specimen and a direct morphological comparison between the Archaeocyathina and the Vauxiidae, we suggest that the supposed Cambrian representatives of horny demosponges, that is, vauxiids, probably, were a progeny lineage of archaeocyathines. They survived the extinction of hypercalcified archaeocyaths due to their ecological adaption to siliciclastic environments. The existence of hypercalcified dictyoceratid ('keratosan') sponge Vaceletia, well known as a 'living archaeocyath', supports such a possibility. □ Archaeocyaths, Cambrian, keratosans, Porifera, verongiids.

Identification and current palaeobiological understanding of “Keratosa”-type non-spicular demosponge fossils in carbonates: with a new example from the lowermost Triassic, Armenia

“…Moreover, a recent study of fossils from the Guanshan Biota (Cambrian Stage 4) suggested that archaeocyaths of the suborder Archaeocyathina, to which D. translucidus also belong, are morphologically very close to vauxiid sponges [63]. The investigated Guanshan fossils can be comfortably assigned to either of these groups.…”

“…5) [2]. These fossils were later diagnosed as the archaeocyath Dictyocyathus translucidus [60], a unique archaeocyath species whose skeleton is always preserved as moulds filled with sparitic cements [61–63]. This exceptionality in archaeocyaths was previously attributed to originally aragonitic mineralogy in the skeleton [61,62].…”

“…Noticeably, the skeletons of vauxiids and related archaeocyaths all show repeatedly occurring hexagonal-dominant meshes [63]. In living non-spicular demosponges, taxa that typically exhibit hexagonal meshes are verongimorphs such as Aplysina [64] and Verongula [65].…”

“…In this case, the non-spicular demosponge interpretation of D. translucidus seems to be reasonable from a taphonomic point of view. Noticeably, the skeletons of vauxiids and related archaeocyaths all show repeatedly occurring hexagonal-dominant meshes [63]. In living non-spicular demosponges, taxa that typically exhibit hexagonal meshes are verongimorphs such as Aplysina [64] and Verongula [65].…”

Recognizing sponge inSpongiostromaGürich, 1906 from the Mississippian of Belgium

“…Vauxiidae includes seven species of Vauxia and one species of Angulosuspongia, restricted to the Cambrian Burgess Shale-type fauna (Yang et al, 2017;Luo et al, 2020;Wei et al, 2021). Recently, Luo et al (2021) suggested archaeocyaths to be hypercalcified keratosan sponges, similar to Recent Vaceletia (Wörheide, 2008). Recognition of Spongiostroma as a keratosan demosponge (1) enhances recognition of fossil sponges, (2) clarifies longstanding confusion between vermiform fabric and clotted microbial fabrics (Pia, 1927;Johnson, 1961;Flügel, 2004;Kershaw et al, 2021), and (3) qualifies the suggestion that Spongiostroma is not a sponge (Neuweiler et al, online preprint).…”