Do you mean invertibrae to vertibrae evolution? Many invertabrates are chordates.
No, I meant what I wrote. Although I'm no expert, I know about invertabrate chordates.
The cambrian explosion took about 40 millions years, it was only sudden geologically speaking. It marked a radiation of diversity in the oceans. There are many possible explainations for why there are not many pre-cambrian fossils. One is that the cambrian explosion marks a point where life became able to mineralise its body to create hard parts that would easily fossilise. Another is that the environment on earth before that time was damaging to fossils. Of course none of these explainations are considered fact and there is lots of debate over this by scientists.
Ok. I won't labor the point, but how do you then explain the sudden appearance of phyla during the Cambrian, if there are no clear ancestors? So we agree for now that this remains a mystery to science, although there are hypothesis?
The cambrian explosion is a mystery and a problem that science seeks to explain, but it is not something that disproves evolution. Tigers and bats suddenly appearing in the cambrian would be a disproof as there would not be enough time for these to evolve. But small sea creatures aren't. So the cambrian explosion is an unsolved problem for evolution, but not a huge problem.
OK, like I already said, I'm no expert but the argument I'm trying to get across goes something like this:
Chordates include all vertebrates (fish, amphibians, reptiles, birds, and mammals) and some invertebrates. According to the most widely accepted model, echinoderms (sea stars, sea cucumbers, etc.) gave rise to chordates (and to hemichordates, as a 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 relatively few 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.
The sources include this, and some conclusions are from Fazul Rana.
# 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.
# Cleveland P. Hickman, Sr. et al., Integrated Principles of Zoology, 6th ed. (St. Louis, MO: The C. V. Mosby Company, 1979), 476-81.
# D. —G. Shu et al., “An Early Cambrian Tunicate from China,” Nature 411 (2001): 472-3.
# D. —G. Shu et al., “Primitive Deuterostomes from the Chengjiang Lagerstatte (Lower Cambrian, China),” Nature 414 (2001): 419-24.
# D. —G. Shu et al., “Primitive Deuterostomes,” 419-24.
Well done for pointing out my mistake of asking for "modern animals". what I really should have emphasised is that I was wanting something like rabbits, or other mammals. Jawless fish are very ancient (none of the earliest fish had jaws) so finding out that there were jawless fish in the cambrian (which I didn't know before) doesn't really ring alarm bells for me. I am sure a lot of other small cambrian sea life still exists in similar forms today as well.
I was just joking with you. I would be disappointed if it was that easy.