Encyclopedia of Evolution.pdf - Online Reading Center

Burgess shale deposit. He hastily gathered a few specimens,
then returned in later summers for more specimens. He took
specimens back to the Smithsonian and studied them. He
recognized their strangeness but classified them into existing
groups of animals. After his death, the Burgess shale
specimens lay in obscurity for many years in the National
Museum of Natural History at the Smithsonian Institution
in Washington, D.C., until they were again examined and
reanalyzed by three paleontologists from Cambridge University
in England: Harry Whittington, Derek Briggs, and Simon
Conway Morris.
Many of the organisms preserved in the Burgess shale
represent groups of invertebrates that are recognizable today,
or are well known from other parts of the fossil record. This
includes: sponges; segmented worms similar to those in the
oceans today; onychophoran worms that are today considered
primitive arthropods; and trilobites, which looked like cockroaches
on the Paleozoic seafloor and which declined during the
late Paleozoic era and vanished in the Permian extinction.
There are possible cnidarians in the Burgess shale, but none of
them are jellyfish (see invertebrates, evolution of).
Burgess shale
Burgess shale organisms, from the Cambrian period, include (A) Pikaia gracilens, a chordate; (B) Hallucigenia sparsa, probably an onychophoran worm;
(C) Opabinia regalis, an arthropod, and (D) Anomalocaris canadensis, another arthropod.
The affinities of many of the Burgess shale organisms
were not immediately apparent. Examples include (see figure
on page 65):
• Anomalocaris canadensis. The name Anomalocaris means
“weird shrimp” because researchers found numerous fossils
of what appeared to be headless shrimp. Other fossils were
found that resembled a pineapple slice and were thought to
be jellyfish. Other fossils had what appeared to be swimming
flaps. It was not until Whittington recognized a fossil
in which two of the above fossils were attached to one
another that he realized all three fossils really came from
one animal: What had been considered shrimp were actually
the front appendanges of the animal, what had been
considered a jellyfish was the animal’s round mouth, both
attached to a body that had flaps. The animal grabbed trilobites
with its big front appendages, and jammed them
into the round mouth. A mechanical model of a reconstructed
Anomalocaris mouth was able to produce a bite
mark on a model of a trilobite that resembled actual damage
known from Cambrian trilobite fossils. Because of the