Cambrian petalonamid Stromatoveris phylogenetically links Ediacaran biota to later animals

Abstract

Macro-organisms of the Ediacaran period (635-541 Ma) were large and morphologically complex, with some living in aphotic habitats, presenting the possibility that they were early animals. However, 'bizarre' Ediacaran morphologies and mouldic preservation have frustrated comparison to later taxa. Consequently, both the positions of Ediacaran biota in the tree of life and the origins of the Metazoa have remained disputed. Here we provide phylogenetic evidence to identify Ediacaran macro-biota as animals, based on 206 new fossils of Stromatoveris psygmoglena from the lower Cambrian Chengjiang Lagerst€ atte. Exceptionally preserved soft-tissue anatomy shows that Stromatoveris was a soft-bodied, radially symmetric animal with multiple, sub-branched petaloids and a differentiated holdfast. Photo-referenced morphological character analysis enables phylogenetic reconstruction of a monophyletic clade designated Petalonamae, that unites Stromatoveris with iconic Ediacaran genera (Rangea, Pteridinium, Ernietta, Swartpuntia, Arborea, Pambikalbae and Dickinsonia) and is placed as sister-group to the Eumetazoa. Therefore, based on phylogenetic bracketing within the Metazoa, the Ediacaran petalonamids are established as animals. From these findings, it follows that petalonamids remained an important component of Cambrian marine ecosystems and that the metazoan radiation can be dated to a minimum age of between 558 and 571 myr.

Cochleatina: an enigmatic Ediacaran–Cambrian survivor among small carbonaceous fossils (SCFs)

“…Thaumaptilon (Conway Morris ) and Stromatoveris (Shu et al . ; Hoyal Cuthill & Han ). The current roster of ‘Ediacaran survivors’ is modest, but nonetheless significant.…”

Oxygen, temperature and the deep-marine stenothermal cradle of Ediacaran evolution

“…This community is primarily dominated by morphologically complex soft-bodied benthic frondose fossils belonging to two recognized groups, the Arboreomorpha and Rangeomorpha. While there are phylogenetic issues with assigning Ediacaran fronds to the Metazoa ( [26], but see [27]), Avalonian assemblages also contain other fossils more likely to be animals, including sponges [28] and bodyand trace-fossil evidence for eumetazoan cnidarians [23]. These fossils appear in the middle Ediacaran ca 571 Ma in deep-water, aphotic slope and basinal facies [22][23][24]29], where they are found in situ, buried by ash beds or rapidly deposited sediments.…”

Why the term “larva” is ambiguous, or what makes a larva?

“…This is caused by the uncertainty of the exact splitting pattern in the early metazoan lineage (Dunn, Giribet, Edgecombe, & Hejnol, 2014;King & Rokas, 2017;Nosenko et al, 2013) Still, it remains at least possible that the adult form of the ancestral metazoan was sessile. This is indicated by the sessile adults of sponges (Porifera), corals (Anthozoa) and possible sessile fossil relatives of comb jellies (Ctenophora; Shu et al, 2006, but see recent reinterpretation by Hoyal Cuthill & Han, 2018). If the ancestral metazoan was indeed sessile as an adult, the blastula stage could be considered as a larval stage.…”