- evidence of vertebrates before the Mid-Lower Cambrian
(translating as "mouth second") are a major animal taxon
that further divide into the echinoderms (e.g., crinoids, starfish,
urchins) and the chordates
(e.g., humans, fish and other vertebrates). The deuterostomes belong
to a larger group within the Animalia
called the Bilateria, owing to bilateral symmetry with a left and
a right side to the body plans: note that some deuterostomes are
bilateral as embryos, later maturing to have radial symmetry.
et. al. (Ref) the Chengjiang fossil-Lagerstätte, report a suite
of fossils, representing at least four taxa, from the Chengjiang
fossil-Lagerstätte that are characterized by a bipartite body,
the anterior section of which has a series of perforations, evidently
precursors of gill slits; note that jawless fish probably did not
occur until the Lower Ordovician.
These fossils appear to be primitive deuterostomes. If so, they
could present the common ancestor of many animals that appeared
and radiated in the Cambrian
Explosion, and ultimately all of Phylum Chordata and the vertebrates.
These discoveries significantly predate previously published reports,
but they also imply that even more primitive vertebrates had evolved
before the mid-Lower Cambrian.
D-G.; Luo, H-L.; Conway Morris, S.; Zhang, X-L.; Hu, S-X.; Chen, L.; Han, J.;
Zhu, M.; Li, Y.; Chen, L-Z. (1999): Lower Cambrian Vertebrates from South China.
Nature 402: 42-46.