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The Explosive Appearance of Skeletal Designs

By Fazale Rana - July 1, 2000

A team of scientists from Franklin & Marshall College (in Pennsylvania), the University of Chicago, and the American Museum of Natural History in New York City has recently reported a new measure of the dramatic biological innovations that took place during the Cambrian Explosion.1

Based on fossils found in southern China and in the Burgess Shale deposits of the Canadian Rockies, biologists know that nearly all the animal phyla (more than 70) known to exist throughout the earth’s history appeared essentially at once about 540 million years ago.2 (Phyla are the categories in the biological classification hierarchy that refer to an organism’s body plan, or architectural make-up.) 

This event, known as the Cambrian “Explosion,” occurred over an extremely narrow window of geological time (~5-10 million years based on western scientific literature and less than 3 million years based on Chinese scientific literature).3 Since then, arguably no new animal phyla have appeared. In fact, about 40 animal phyla have disappeared since that time.

Along with the “sudden” appearance of animal phyla, the Cambrian period was the first time that animals with skeletons showed up in the Earth’s history.4 A range of features define a skeleton.5 A skeleton may be 1) internal or external; 2) rigid or flexible; 3) formed with one, two or multiple elements; 4) comprised of rods, plates and solid three-dimensional parts; 5) grown by accretion, molting, or remodeling; and 6) composed of different chemical materials such as silica, calcium carbonate, calcium phosphate and chitin.

Based on these and other characteristics, the above team of researchers constructed a “skeletal space,” a mathematical space that defines all possible skeletal designs. From this skeletal space, 182 possible skeletal designs were identified. Interestingly, of these 182 possibilities, 146 appeared during the Cambrian Explosion (based on analyses of 104 fossil genre recovered from the Burgess Shale Cambrian site). That is, over 80 percent of all the possible skeletal designs appear suddenly in the fossil record—during a period of less than 15 million years. Land animals and vertebrates, which fill the remaining skeletal space, are underrepresented in the Burgess Shale fauna. Thus, researchers consider the skeletal designs that do show up during the Cambrian Explosion essentially maximal in number.

The Cambrian Explosion has long been an enigma for biology.6 The more we learn about the introduction of complex animals on Earth, the more puzzling the Cambrian event becomes for evolutionary biologists. The explosive appearance of the nearly all possible skeletal designs in the Cambrian fauna defies a natural process explanation.  Yet, this is exactly what one would expect to see in the fossil record if the God of the Bible were responsible for the creation of animal life on Earth.

  1. R.D.K. Thomas, Rebecca M. Shearman, and Graham W. Stewart, “Evolutionary Exploitation of Design Options by the First Animals with Hard Skeletons,” Science 288 (2000): 1239-42.
  2. Fazale R. Rana and Hugh Ross, “The Cambrian ‘Explosion’ and Why It Means So Much for Christians,” (An Interview with Dr. Paul Chien), Facts for Faith (Quarter 2, 2000): 15-17.
  3. Fazale R. Rana, “Cambrian Flash,” Connections 2, no. 1 (2000): 3.
  4. Richard Cowen, History of Life, 3rd ed. (Malden, MA: Blackwell Science, 2000): 60-64.
  5. Thomas, Shearman, and Stewart, 1239.
  6. Simon Conway Morris, “The Cambrian ‘Explosion’: Slow-Fuse or Megatonnage?” Proceedings of the Natural Academy of Sciences USA 97 (2000): 4426-29.

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