this Cambrian animal seems familiar, it is for good reason. It looks
like Naraoia compacta (described by Walcott in 1912) from the Burgess
Shale. This would make it a member of a clade of animals known as
Nectaspida, an order of soft-bodied Arthropods, closely related
This specimen shows the two complex branching
digestive glands and the gut diverticula, which is even more rarely
preserved. The right portion of the head shield is turned in a bit,
but otherwise is a unusaully well preserved specimen.
prevailing view is that the Nectaspida are a sister group to the
clade which includes the calcified trilobites. The revised Treatise
adopts the tactic of treating the naraoiids as a family within the
class Trilobita, order "uncertain," thereby acknowledging
a systematic position within the class, but allowing the formal
definition of Trilobita to be based upon the characters of calcified
forms (Fortey 1997, p. 294).
your further study:
R.A. 1997: Classification. In Whittington, H.B. et al. 1997: Treatise
on Invertebrate Paleontology Part O Arthropoda 1 Trilobita, Revised,
Volume 1: Introduction, Order Agnostida, Order Redlichiida. The
Geological Society of America and The University of Kansas.
Stephen Jay 1989: Wonderful Life. Penguin. 347 pp.
C.D. 1912: Middle Cambrian Branchiopoda, Malacostraca, Trilobita
and Merostomata. Smithsonian Miscellaneous Coll. Publ. 2051, v.
J.-Y.; Zhou, G.-Q. 1997: Biology of the Chengjiang Fauna. In Chen,
J.-Y.; Chen, Y.-N.; Van Iten, H. (eds.) 1997: The Cambrian Explosion
and the Fossil Record. Bulletin of the National Museum of Natural
Science, 10. Taichung, pp. 11-105
a more extensive discussion and references, visit Sam
Gon's web site.
wrote: "Even if complexity is only a drift away from a constraining left
wall, we might view trends in this direction as more predictable and characteristic
of life's pathway as a whole if increments of complexity accrued in a persistent
and gradually accumulating manner through time. But nothing about life's history
is more peculiar with to this common (and false) respect expectation than the
actual pattern of extended stability and rapid episodic movement, as revealed
by the fossil record."