Burgess Shale Early Cambrian Explosion Wiwaxia Opabinia Pleurocystites Anomalocaris Laggania Hallucigenia Olenoides

More than 1/2 BILLION years old, the fossils of the Burgess Shale fauna preserve for us an intriguing glimpse of early animal life on Earth. These fossils are named after a Cambrian rock formation (the Burgess Shale) that is located in the western Canadian Rockies. This is our first sight of modern multicelled creatures. Most of the animals have few hard parts and do not normally create fossils.

photo of the Burgess Shale Diorama at National Museum of Natural History Museum , Smithsonian Institution.

Sidneyia is a large , up to 13cm, predator. The spines along the walking legs were used to catch and eat ostracods and trilobites. Canadapis is crustracean digging in sediment for food. Over 4000 fossils were found. Aysheaia is loboform and is most likely a memeber of the minor Phylum Onychophora.

Opabinia with its five eyes is a strange looking one indeed. Wielding a long flexible proboscis tipped with grasping spines. It was about 3 inches long. It may be related to Laggania and its close relative Anomalocaris are some of the most widely distributed of the Burgess Shale animals. It is the largest known Burgess Shale animal. Some related specimens found in China reach a length of six feet! The giant limbs in front, which resemble shrimp tails, were used to capture and hold its prey. A formidable mouth on the undersurface of the head had a squared ring of sharp teeth that could close in like nippers to crack the exoskeleton of arthropods or other prey. With those large eyes and a body half flanked with a series of swimming lobes, this must have been an active, formidable predator. Originally the different parts were identified as 3 separate animals, trunk, jaws and front limbs were preserved separately. Only later was a connected specimen recovered.

Wiwaxia looks like a slug armored with spines called sclerites. The longer spines project in two rows along the back, and evidently provided some protection from predators. The rest of the upper (dorsal) surface is covered with small, flat, overlapping hard plates, termed sclerites. Each of these little scales was attached with a root-like base and we assume Wiwaxia grew by molting these plates from time to time. Since there are none on the bottom (ventral) surface, the animal partly resembles the slug, a member of the mollusk family. A more recent relationship proposal is a relationship with an annelids. The sclerite being similar in microstructure to the chitinous bristles (chaetae) of earth worms. It did have an anterior jaw with two rows of teeth on the ventral surface, suggesting it was another bottom feeder. Fossil sizes range from 1/8 to 2 inches.

Originally the Hallucigenia was thought to have stood on its spines, with the tentacles upward. Later studies have shown that the "tentacles" are actually feet, It is less than three millimeters long, making it one of the smaller creatures in the Burgess Shale. At one end there is a bulbous "head" which is a round mass. This connects to the cylindrical trunk of the Hallucigenia, which, on the top has seven pairs of spines pointing upward and outward. These conical spines are embedded into the trunk, and are fairly long when compared to the rest of the Hallucigenia. Below each pair of spines there is a tentacle except that the last tentacle is offset from the pair of spines. Behind these tentacles there are three pairs of much shorted tentacles, and then the trunk narrows and curves upward. The tentacles have pincers at their tips, and there is a hollow tube in each one which is connected to the gut. It and Aysheaia are thought to be loboforms and related to the velvet worms an obscure phylum of caterpillarish looking animals found in southern hemisphere. Pleurocystites is a good example of the sedentary filter feeders that dominate Paleozoic seas. Sea Lilies belong to the same family as starfish and sea urchins. They decline sharply at the end of the Paleozoic.

Olenoides is decribed by Stephen Gould in his book 'Its a Wonderful Life' as a standard trilobite The long, curved antennae were well preserved in the Burgess Shale. The middle legs, near their base, bore a series of spines that could be used to grasp the soft-bodied animals it preyed on and then to move them forward toward the mouth. The thin limbs tell us that this was not a swimmer. Instead, it was an active predator and scavenger moving about the muddy seafloor.