So what may have trilobites done "wrong" that caused them to have poor reproductive success? A paleontologist has found specimens that appear to be moulting with a split down the middle. If a trilobite got stuck getting out of its moulted carapace, it would have one line of legs out and look like a pita sandwich! In struggling, it would only be able to scramble or swim in circles, not an adaptive way to get away from big, fast predators!
BELOW: Mud dwellers like the priapulid worms (one burrowing with its spiny proboscis - Selkirkia) lurk in their burrows while the worm Louisella pumps sea water through its horizontal burrow. Selkirkia is housed in a parchment-like sheath. Two polychaetes of the genus Burgessochaeta are visible, one head down in its burrow with rear tentacles exposed. A scoop from the time machine that made these pictures possible is seen sampling the sea floor.
BELOW: The lobopodan Asheaia (a possible relative of living velvet worms) crawls over the blue sponge Vauxia. Its prongs around the mouth are thought to be specialized for feeding on sponges. The feathery sea pen Thaumaptilon, a distant relative of sea anemones and corals, dominates the scene. Dinomischus (yellow), Mackenzia (green), Chancelloria (purple) Pirania (brown with spicules), Choia (pincushion-like) represent sessile and mudsticker members of the Burgess community. Two trilobites wander among the mudstickers.
BELOW: Swimming members of the community. The shelled arthropod Ordaria swims upward while comb jellies Ctenorhabdotus drift nearby. The polychaete worm Canadia creeps toward toward the enigmatic Nectocaris. A gelatinous Eldonia (primitive echinoderm?) drifts in the left middle ground below two Pikaia that are primitive chordates (ancestral to vertebrates). In the forground is Dinomischus (a filter feeder?) and Pirania with some symbiotic brachiopods attached to its spicules. Note that spines are very popular with the Burgess fauna.
We leave the unique Burgess fauna, realizing that we have run out of peanut butter and jelly sandwiches and need to return to our own time for some fluffernutters. Between them and our era lie five mass extinctions and numerous smaller extinctions. As Raup and Sepkowski have calculated, each species gets about 20 million years to live and then faces extinction from a variety of factors.
|TOP | PREVIOUS |