Origin and early diversification of the phylum Cnidaria Verrill: major developments in the analysis of the taxon's Proterozoic–Cambrian history

Abstract

Diploblastic eumetazoans of the phylum Cnidaria originated during the Neoproterozoic Era, possibly during the Cryogenian Period. The oldest known fossil cnidarians occur in strata of Ediacaran age and consist of polypoid forms that were either nonbiomineralizing or weakly so. The oldest possible anthozoans, including the genus Ramitubus, may be related to tabulate corals and occur in the Doushantuo Lagerstätte (upper Doushantuo Formation, South China), the age of which is poorly constrained (approximately 585 Ma?). Conulariid scyphozoans may first appear as early as 635–577 Ma (Lantian Formation, South China). A definite conulariid, most similar to Palaeozoic species assigned to the genus Paraconularia, occurs in association with the possible scyphozoan, Corumbella werneri, in the latest Ediacaran (c. 543 Ma) Tamengo Formation of Brazil. Basal Cambrian (c. 540 Ma) phosphorites in the upper Kuanchuanpu Formation (South China) yield solitary polyps of the oldest probable anthozoan (Eolympia pediculata), which appears to have been a stem hexacorallian. This same formation contains fossils interpreted by some authors as pentaradial cubozoan polyps; however, both the oldest known cubozoans and the oldest hydrozoans, all medusae, may actually occur in the Cambrian (Series 3, c. 505 Ma) Marjum Formation (Utah, USA). Although these recently published palaeontological data tend to corroborate the hypothesis that Cnidaria has a relatively deep Neoproterozoic history, the timing of major internal branching events remains poorly constrained, with, for example, the results of some molecular clock analyses indicating that the two cnidarian subphyla (Anthozoaria and Medusozoa) may have originated as many as one billion years ago. Further progress towards elucidating the evolution and early fossil record of cnidarians may accrue from: (1) an intensive search for phosphatized soft parts in possible anthozoans from the Ediacaran Doushantuo Formation; (2) an expanded search for Ediacaran conulariids; and (3) additional detailed analyses of the taphonomy and preservation of Ediacaran and Cambrian cnidarians, including possible pentaradial cubozoan polyps from the Fortunian upper Kuanchuanpu Formation.

A problematic cnidarian (Cambroctoconus; Octocorallia?) from the Cambrian (Series 2–3) of Laurentia

“…They suggested that Medusozoa (Scyphozoa + Hydrozoa) formed a sister group to Octocorallia, and that these together were a sister group to Hexacorallia (Kayal et al, 2013). The phylogeny was cited as potentially supporting the 'polyp before medusa' hypothesis of cnidarian evolution (Ax, 2012), a theme taken up by Dzik et al (2017) in the context of the fossil record of the tubular cnidarian Sphenothallus Hall, 1847 and related Lower Paleozoic taxa (Tynan, 1983;Van Iten et al, 2014). Zapata et al (2015) restated the monophyly of Anthozoa, Octocorallia, and Hexacorallia.…”

“…Cnidarians have a geological record extending back to the Ediacaran (Van Iten et al, 2014, 2016aLiu et al, 2014;Grazhdankin, 2016;Han et al, 2016;Dzik et al, 2017), but the heavily calcified groups of tabulate and rugosan corals that dominate the Paleozoic fossil record first appear in the Ordovician (Scrutton, 1997(Scrutton, , 1999. There are, however, many mineralized Cambrian fossils, particularly in the early Cambrian, that have been considered as possible anthozoans, but their relationships to the major zoantharian and octocorallian groups are uncertain (Zhuravlev et al, 1993;Scrutton, 1997Scrutton, , 1999Debrenne and Reitner, 2001;Han et al, 2016).…”

IsHaootia quadriformisrelated to extant Staurozoa (Cnidaria)? Evidence from the muscular system reconsidered

“…Fossil muscular impressions of Cambrian cnidarians, such as those of scyphomedusae, have an organization strikingly clear and similar to extant animals [14,15]. The impressions of H. quadriformis are considerably more complicated, probably because of its plane of preservation and possible superposition of morphological structures, making it difficult to reliably reconstruct muscular organization.…”

New aspects of Neoproterozoic-Cambrian transition in the Corumbá region (state of Mato Grosso do Sul, Brazil)

“…4a-b) also occurs in the Tamengo Formation, and has been interpreted as a cnidarian, possibly related to the Scyphozoa Walde et al, 1982;Babcock et al, 2005). Van Iten et al (2014) interpreted this fossil as a colunariid scyphozoan, related to other non-erect Ediacaran fossils such as the vendozoan genera Phyllozoon (Jenkins and Gehling, 1978) or Dickinsonia (Sprigg, 1947). Since, in 2012, three-dimensional specimens of Corumbella werneri were found together with two-dimensionally preserved material in a quarry on the western edge of Corumba, it is evident that this species does not belong to the conulariids, but to cloudinids (personal comm.…”