The Cambrian "Explosion" is looking less so

The Cambrian "Explosion" is looking less so

The Cambrian "explosion", as evidenced by the fossil record of specific aspects of the Burgess Shale, has been interpreted as representing the relatively rapid appearance of most major Phyla over the course of several million years.  The fossils that began to "emerge" some 505 million years ago were seen as an explosion of diversity.  Prior posts have noted the evidence that the "emergence" may have begun many millions of years prior, but that the fossil record was less well defined because many of the earlier animals did not have hard body parts which easily fossilized.

Researchers have now found additional fossil beds 40 km from the Burgess fossil beds that shed additional light on this period of time.  About half of the animals found in the new fossil beds are found in other Burgess outcropings, but in difference abundances.  The new fossils also include 8 previously unknown taxa [a population, or group of populations of organisms which are usually inferred to be phylogenetically related and which have characters in common which differentiate the unit (e.g. a geographic population, a genus, a family, an order) from other such units].

Until now, paleontologists believed that the Burgess fossils were so well preserved because the animals settled in thick deposits at the bottom of an ancient ocean protected by a submarine cliff.  The new fossils were not formed in the presence of a cliff, suggesting preservation is possible in other environments.  This different environment also shows that the organisms lived and died in these different environments.  Since much of this new area remains unexplored, it may shed further light on the evolution of animals over time.  Further, as the researchers note:  "The low diversity of both the benthic taxa and the ichnofauna, which includes diminutive trace fossils associated with carapaces of soft-bodied arthropods, suggests a paleoenvironment with restrictive conditions. The Stanley Glacier assemblage expands the temporal and geographic range of the Burgess Shale biota in the southern Canadian Rockies, and suggests that Burgess Shale-type assemblages may be common in the 'thin' Stephen Formation, which is regionally widespread."

The report on this initial review of this "thinner" aspect of the "Stephen Formation" can be found at http://geology.gsapubs.org/content/38/9/811.abstract.