Sicyophorus rarus (Luo & Hu, 1999), as the species name implies,
is one of the rarer animals of the Chengjiang
shales and from Phylum Priapulida. The
priapulids are a group of non-segmented worms whose modern-day
examples can reach 30 cm in length, and live in both shallow
and deep marine
sands as carnivores. Individuals of this small group, much like
Palaeopriapulites parvus, parvus meaning small in
the Latin, are normally less than 10 mm long and exhibit a figure
eight shape. This one possesses a coiled gut not seen in Palaeopriapulites
parvus. Some researchers believe that Sicyophorus rarus is
a junior synonym of Protopriapulites
in 1984, the Chengjiang Biota now ranks as the most diverse
faunal fossil assemblage of all the Burgess Shale like deposits.
is also some 10 million years older than the Burgess Shale.
Like the Burgess Shale, non-mineralized soft tissue parts are
extraordinarily well preserved with high resolution as aluminosilicate
films, sometimes with oxidized iron content. Various taphonomic
processes leading extensive preservation of soft tissue have
been proposed, including rapid death by asphyxia followed
by rapid burial in anoxic sediment undisturbed by turbidity.
Chengjiang biota is dominated by phyla Arthropoda and Porifera.
There are seven lobopodians,
more than any other Lagerstätte that
some scientists elevate to the phylum rank Lobopodia, and
seven members of the extinct phylum Vetulicolia.
Members or potential members of phyla Priapulida, Nematomorpha,
Hyolitha, Hemichordata, Echinodermata, Ctenophora, Chordata,
Cnidaria, Chaetognatha, and Brachiopoda are found. A large
number of enigmatic animals of uncertain affinity are found
as well, some of which may represent failed evolutionary
experiments, or even new phyla that did not persist for long
in the early
to middle Cambrian, or were rapidly replaced by more derived
forms. Among the diverse Maotianshan Shales fauna, of utmost
important are the putative early chordates, particularly Haikouella,
potentially an ancestor to or the earliest craniate chordate.
Myllokunmingia and Haikouichthys are interpreted as early
Craniata, and possibly very primitive agnathids, the progenitor
fishes and all vertebrates.
see: Chengjiang Maotianshan Shales, Chengjiang