CNIDARIA

Benton, MJ, Donoghue, PCJ, Vinther, J, Asher, RJ, Friedman, M & Near, TJ, 2015, Constraints on the timescale of animal evolutionary history, Palaeontologia Electronica (Florence, Italy) 15 (1), pp. 1-107 : 16-17

CROWN CNIDARIA (3)

Node Calibrated. The clade comprised of Anthozoa and Medusozoa, their last common ancestor and its descendants. The monophyly of crown Cnidaria is well established on the basis of anatomical and molecular evidence (Daly et al., 2007).

Fossil Taxon and Specimens. Olivooides multisulcatus (Geological Museum of Peking University: GMPKU3083-GMPKU3090), Dengying Formation, Fortunian Stage, constituting a range of embryonic and post-embryonic developmental stages.

Phylogenetic Justification. Olivooides is known from embryonic and post-embryonic stages of development, including a polyp theca, characteristic of scyphozoans, and a medusa stage ( Dong et al., 2013).

Minimum Age. 529.0 Ma

Soft Maximum Age. 636.1 Ma

Age Justification. Olivooides multisulcatus co-occurs with Anabarites trisulcatus , which is indicative of the middle of the Fortunian Stage of the Terreneuvian Series, the first of the Cambrian. The top of the Fortunian Stage is dated at 529.0 Ma (Peng et al., 2012).

A soft maximum constraint is based on the maximum age interpretation of the Lantian Biota (Yuan et al., 2011). This, together with the Doushantuo Biota (Yuan et al., 2002), provides a series of Lagerstätten preserving the biota in Orsten- and Burgess Shale-like modes of fossilization. None of these Lagerstätten, least of all the Lantian, preserves anything that could possibly be interpreted as even a total group eumetazoan and on this basis we define our soft maximum constraint at 635.5 Ma ± 0.6 Myr (Condon et al., 2005) and, thus, 636.1 Ma.

Discussion. The oldest possible record of a cnidarian is Sinocyclocyclicus guizhouensis from the Ediacaran Doushantuo Formation (Xiao et al., 2000; Liu et al., 2008) but the evidence of its affinity to Cnidaria amounts to little more than its tabular structure, which is reminiscent of tabulate corals. Putative Ediacaran medusoid cnidarians (Wade, 1968; Glaessner, 1971) have been reinterpreted as microbial communities ( Grazhdankin and Gerdes, 2007) or trace fossils ( Jensen et al., 2002). Frondlike Ediacarans have been interpreted as pennatulacean cnidarians, but this comparison is unconvincing (Antcliffe and Brasier, 2007, 2008). The terminal Ediacaran skeletonizing organisms Cloudina , Namacalathus, Nemapoika , and Sinotubulites have been considered total-group cnidarians (Wood, 2011), but this comparison has no material basis. Liu and colleagues (2010) described c. 565 Ma trace fossils, which they interpret as evidence of a muscular metazoan-grade organism, drawing particular comparison to polypoid cnidarians, though they later retreat from arguing that these traces necessarily indicate the existence of animals ( Liu et al., 2010). Thus, Olivooides multisulcatus , known from embryonic and post-embryonic stages of development including a polyp theca and medusa stage, is the oldest phylogenetically secure crown-cnidarian. Its pentaradiate symmetry has led to speculative hypotheses of an affinity to echinoderms, however, O. multisulcatus co-occurs with the tetraradial Quadrapyrgites , to which it is comparable in all aspects bar symmetry.