Unranked clade (stem group cnidarians)
Thaumaptilon was first interpreted as a Cambrian member of the frondose Ediacaran Biota, related to cnidarians and particularly to a group of modern anthozoans called pennatulaceans or sea pens (Conway Morris, 1993). This connection is no longer widely accepted (Antcliffe and Brasier, 2008); Thaumaptilon has also been proposed as a critical link between Ediacaran fronds and ctenophores (Dzik, 2002). A position in the cnidarian stem group (i.e. more primitive than the anthozoans) has been supported by the discovery of similar fossils in the Chengjiang Biota (Shu et al., 2006).
Thaumaptilon – from the Greek thauma, “wonderful,” and ptilon, “soft feather,” after its feather-like appearance.
walcotti – after Charles Walcott, discoverer of the Burgess Shale.
Holotype –USNM468028 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott Quarry on Fossil Ridge.
Brief history of research:
Walcott had studied and photographed Thaumaptilon, but never published his work. The fossil specimens were formally described in 1993 by Conway Morris, who had also alluded to them in previous work (1979; 1989; 1990).
Thaumaptilon is an oblong frond that somewhat resembles a feather; it is bilaterally symmetrical, with a central axis supporting a number of lateral branches. The branches appear to be connected to one another by narrow canals. A blunt holdfast attached the animal to the sea floor. Of the three known specimens, the largest is 21 cm tall and reaches 5 cm across; the smaller specimens – presumed to be juveniles – are only a few centimetres long. The frond is flattened, and tapers slightly towards its tip. It consists of about three dozen branches angled at 45º to the central axis, and primarily grew by inflation – perhaps with some addition of branches by apical budding. Unlike modern sea pens, Thaumaptilon’s branches attach to a common base. Lines of pustules on one side of the frond have been interpreted as retracted zooids (individual members of a colonial organism), which are arranged very haphazardly in comparison to the neat combs seen in modern sea pens.
Only three specimens are known.
The holdfast would have anchored the organism to the soft sediment of the sea floor, and could perhaps contract to adjust the height and angle of the frond. Based on the interpretation of the pustules as zooids, a colonial, suspension-feeding lifestyle has been proposed. It has been suggested that Thaumaptilon could retract into its stem when threatened, for protection (Conway Morris, 1998).