Chordate Fossils Foil Theory

Chordate Fossils Foil Theory

China’s rich cache of fossils provides paleontologists with a window to the time in Earth’s history when complex animal life first appeared. As scientists peer through this window, they see a scene that defies naturalistic explanation.

The fossils discovered in China, along with those in British Columbia and elsewhere, present an unexpected picture: nearly every animal phylum ever to exist in Earth’s history appeared suddenly about 540 million years ago.1 A phylum refers to the level in the biological classification system describing an organism’s body plan or architectural makeup. Some paleontologists report that more than seventy animal phyla (strictly marine animals) appeared in less than 2-3 million years. Scientists refer to this dramatic introduction of animal phyla as the Cambrian Explosion—biology’s “big bang.”

Paleontologists had thought the Cambrian event involved only invertebrates (organisms lacking a backbone). However, the recent discovery of jawless vertebrates from the lower (earlier) Cambrian deposits in China changed their view. Researchers must now account for the simultaneous appearance of both groups.2

The phylum Chordata holds special interest for paleontologists researching the origin of animal life. Chordates include all vertebrates (fish, amphibians, reptiles, birds, and mammals) and some invertebrates. To understand the origin of chordates, therefore, is to understand the beginning of some of the most important organisms in Earth’s history. For this reason, evolutionary biologists peer eagerly through this window of time. They especially hope to see the connection between chordates and the other invertebrate phyla.

According to the most widely accepted evolutionary model, echinoderms (sea stars, sea cucumbers, etc.) gave rise to chordates (and to hemichordates, as an evolutionary side-branch).3 This model posits that a sessile (attached to the seafloor) echinoderm brought forth a sessile chordate (classified as a urochordate), similar to modern-day tunicates (sessile invertebrates with a free-swimming larval form). The urochordate then gave rise to a free-swimming cephalochordate, which in turn produced jawless vertebrates, followed by jawed vertebrates.

The prediction for the fossil record, in light of the evolutionary model for chordate origins, calls for echinoderms, urochordates, hemichordates, cephalochordates, jawless vertebrates, and jawed vertebrates to appear sequentially. Given the extensive differences among these groups, their first occurrence in the fossil record should be separated by long time periods, much longer than the 2-3 million years shown by the Cambrian Explosion.

The China discoveries show, instead, the co-existence of echinoderms, hermichordates, cephalochordates, and jawless vertebrates in the earliest part of the Cambrian era.4 And now Chinese paleontologists have added urochordates to this list with the discovery of a tunicate in lower (earlier) Cambrian rocks.5 Before the Cambrian era, no such animal groups existed on Earth. In other words, early in the Cambrian period, when complex animal life first appeared, the kinds of creatures that should have given rise (according to evolutionary theory) to the jawed vertebrates emerged concurrently.

To compound this problem, Chinese paleontologists now recognize an additional phylum (Vetulicolia) as part of the Cambrian event.6 This taxa’s features place it at the base of the chordate evolutionary tree. This makes the Cambrian explosion that much more dramatic. In the words of the Chinese scientists, “the co-occurrence of stem-group deuterostomes [Vetulicolia] and agnathan [jawless] fish are consistent with an ‘explosion’ of metazoan body plans in the latest Neoproterozoic and early Cambrian.”7

What researchers see as their view through the window of time grows clearer is the sudden and simultaneous appearance of echinoderms, hemichordates, urochordates, cephalochordates and jawless vertebrates in the fossil record. This image, with its observable data, confounds a naturalistic explanation but conforms to a biblical creation model that asserts the divinely orchestrated introduction of complex animal life on Earth.

  1. Fazale Rana and Hugh Ross, “The Cambrian ‘Explosion’ and Why It Means So Much for Christians,” Facts for Faith 2 (Q2 2000), 15-17.
  2. D. –G. Shu et al., “Lower Cambrian Vertebrates from South China,” Nature 402 (1999): 42-46; Jun-Yung Chen et al., “An Early Cambrian Craniate-like Chordate,” Nature 402 (1999): 518-22.
  3. Cleveland P. Hickman, Sr. et al., Integrated Principles of Zoology, 6th ed. (St. Louis, MO: The C. V. Mosby Company, 1979), 476-81.
  4. Fazale R. Rana, “Cambrian Flash,” Connections, vol. 2, no. 1 (2000), 3; Fazale “Fuz” Rana, “Extinct Shell Fish Speaks Today,” Connections vol. 3, no. 2 (2001), 1-2.
  5. D. –G. Shu et al., “An Early Cambrian Tunicate from China,” Nature 411 (2001): 472-3.
  6. D. –G. Shu et al., “Primitive Deuterostomes from the Chengjiang Lagerstatte (Lower Cambrian, China),” Nature 414 (2001): 419-24.
  7. D. –G. Shu et al., “Primitive Deuterostomes,” 419-24.