Anatomy and affinities of a new 535‐million‐year‐old medusozoan from the Kuanchuanpu Formation, South China

Abstract

We describe here Sinaster petalon gen. et sp. nov., a new embryonic form from the c. 535 million-yearold Kuanchuanpu Formation of South China (Ningqiang, Shaanxi Province). The excellent three-dimensional, phosphatic preservation of these microfossils allowed us to use x-ray microtomographic techniques to make accurate reconstructions of their internal structures and to compare their anatomy point-by-point with that of extant cnidarians and other animal groups. Sinaster petalon has anatomical features typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, accessory septa, gonad-lamellae, tentacle buds and perradial pockets. Although Sinaster cannot be straightforwardly assigned to any crown-group within Medusozoa, the presence of marginal lappets and endodermal lamellae suggests that it is closer to Cubozoa and Scyphozoa than to any other group of modern cnidarians. The tentative placement of Sinaster within the stem-group Cubozoa is justified by the presence of a velarium supported by a frenulum. The cubozoan affinities of Sinaster are also supported by cladistic analysis.

An intermediate type of medusa from the early Cambrian Kuanchuanpu Formation, South China

“…(, ) and Wang et al . (). All specimens are deposited at the Early Life Institute, Northwest University, China (ELI).…”

“…; Wang et al . ). It should be also noted that most internal structures seen in our embryos are well expressed externally (e.g.…”

“…the apertural lappets connected with the perradial frenula can be seen along the subumbrellar margin of Sinaster : see Wang et al . ). This configuration is again hardly consistent with an artefactual origin.…”

“…Another argument that goes against taphonomy bias is that these diagnostic features also occur in Sinaster (Wang et al . ) another medusozoan from the Kuanchuanpu biota. However, we are fully aware of two things that may lead to misleading or inaccurate interpretations.…”

The negligence and lazy of the Administration: the greatest danger to the conservation of the unique lagerstätte sites

“…3). Cordubia gigantea from Constantina (Sevilla) is the oldest Cambrian impression of medusozoan known and probably coeval with the embryonic form of medusozoan phosphatized discovered in the Terreneuvian of South China (Wang et al, 2017).…”