I would like to correct something here. Vertebrates did not appear
suddenly fully formed in the fossil record. A vertebrate is defined as an
animal that has a backbone. A vertebrate is a member of the chordata. All
vertebrates are chordates but not all chordates are vertebrates. (I would
refer you to Robert Carroll, Vertebrate Paleontology and Evolution, p. 18)
Living examples of invertebrate chordates include Amphioxus, tunicates and
pterobranchs.
Since the invertebrate chordates have no bones, their fossil record has
been sparse. In 1995 one was found that is in the right place at the right
time to represent the pre-vertebrate animal.
The first chordate recorded from the Early Cambrian is the cephalochordate
Yunnanozoon lividum from the 525 million-year-old Chengjiang fauna.
Cordate features of Yunnanozoon are a notochord and an expanded
filter-feeding pharnyx with an endostyle. Segmented musculature and
metameric branchial arches are shared with cephalochordates and craniates.
Metameric gonads and an anteriorly extended notochord indicate
cephalochordate affinities. Yunnanozoon expands the range of
cephalochordate morphology known from the younger Pikaia gracilens and
crown group forms such as amphioxus. Our identification predicts that other
chordate clades (tunicates and craniates) had evolved by the Late
Atdabanian, in the main burst of the Cambrian Explosion" ~ J. Y. Chen, et
al, "A Possible Early Cambrian Chordate," Nature, 377, Oct. 26, 1995
To the best of my knowledge the oldest known vertebrate comes from the late
Cambrian. Of the early invertebrate chordates, there are major differences
between them and the later vertebrates.
"Cephalochordates do not have a heart; blood flow is maintained by
contractile tissue at the base of the aortic arches. The general geometry
of the circulatory system is similar to that of primitive vertebrates, but
there are no capillary beds, and both red blood cells and hemoglobin are
missing from the blood. Oxygen is carried in solution in the body fluids."
~ Robert L. Carroll, Vertebrate Paleontology and Evolution, (San Francisco:
W. H. Freeman and co., 1988), p. 19
So, to claim that vertebrates appear in modern form, fully differentiated
at their start, ignores the latest data of which I am aware.
glenn
Foundation, Fall and Flood
Adam, Apes and Anthropology
http://www.flash.net/~mortongr/dmd.htm
Lots of information on creation/evolution