The Burgess Shale - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 43

Opabinia , which used its nozzle-like
proboscis to search for food. Trophic
analysis by Conway Morris (1986)
identified several feeding types including:
filter feeders, dominated by the sponges;
deposit feeders, dominated by arthropods
(deposit collectors) and mollusks (deposit
swallowers); scavengers such as the
lobopods Hallucigenia and Aysheaia ; and
lastly, predators such as the giant
Anomalocaris , large arthropods (such as
Sidneyia ) and the priapulids. The
important role of predation evident in the
Burgess Shale ecological framework
provides the main contrast with other
Cambrian (shelly) assemblages.

1998, Figure 86). Perhaps these animals
are telling us that mollusks, annelids and
brachiopods are phylogenetically closer
than had been supposed? Molecular
biology supports this conclusion.

Chengjiang, southern China
'Discovered' in the same year, 1984
(although actually known since 1912), the
Chengjiang Fossil-Lagerstätte, best
exposed at Maotianshan, near Kunming,
in Yunnan Province, southern China, also
yields abundant soft-bodied 'Burgess
Shale-type' fossils (see Chen and Zhou,
1997; Hou et al ., 2004). Although of
similar age to the Sirius Passet assemblage
(Lower Cambrian, Atdabanian Stage),
many of the characteristic Burgess animals
are known from Chengjiang (including
complete specimens of Hallucigenia and
Anomalocaris ), in addition to new
Chinese genera of arthropods, worms,
sponges, brachiopods and so on. The
faunal similarity is remarkable because the
South China craton would have been
thousands of kilometres from the
continent of Laurentia (comprising North
America and Greenland).
Among several new groups, a new
phylum, Vetulicolia , was proposed by Shu
et al . (2001) to include segmented,
arthropod-like metazoans which had
obvious gill slits, suggesting a deutero-
stome affinity. But perhaps the most
surprising element of the fauna was
reported by Shu et al . (1999): the discovery
of agnathan fish (previously known from
the Lower Ordovician), illustrating that
even the vertebrates appeared during the
Cambrian Explosion.
Fossil preservation is spectacular with
reddish-purple impressions on fine orange
shale, and again appears to be the result of
rapid, live burial in catastrophic turbidity
flows. The Chengjiang animals probably
lived in the area of their burial, which was
adjacent to a delta front. The 50 m (160 ft)
thick Maotianshan Shale Member of the
Yu'anshan Formation consists of thin,
graded mudstone layers, recording short
episodic sedimentation events.

C OMPARISON OF THE B URGESS
S HALE WITH OTHER C AMBRIAN
BIOTAS
Burgess Shale-type assemblages have since
been discovered at about 40 localities
worldwide, but two are of special
significance.

Sirius Passet, northern Greenland
Discovered in 1984 by the Geological
Survey of Greenland near J P Koch Fjord
in Peary Land, north Greenland, this
locality, now known as Sirius Passet, was
first seriously collected by a 1989
expedition. It soon became apparent that
this was another predominantly soft-
bodied Cambrian fauna, also seemingly
deposited in deep water muds adjacent to
a shallow carbonate bank, and more than
3,000 specimens were collected from what
is now termed the Buen Formation.
Significantly, however, this fauna is of
Lower Cambrian age (Atdabanian), some-
what older than the Burgess Shale,
revealing that the Cambrian Explosion was
well underway by this time.
One of the first and most intriguing
specimens to be discovered at Sirius Passet
was Halkieria , a slug-like animal ( 46 ) with a
dorsal coat of scale-like sclerites just as in
Wiwaxia ( 45 ). But, at either end of the long
body is a shell looking remarkably like an
inarticulate brachiopod (see Conway
Morris and Peel, 1990; Conway Morris,