Some have argued that echinoderm diversity is an Ordovician phenomenon: linked to the Great Ordovician Diversification. Others make the case for the radiation to have initiated earlier. All seem to be agreed that the origin of echinoderms is shrouded in uncertainty. One major problem is that the relevant fossils are unfamiliar and often poorly preserved and there are often doubts about their classification. However, in June 2010, research was reported dealing with Middle Cambrian echinoderms from Spain.
"The new Spanish data suggest that a number of the clades involved in [the Great Ordovician] diversification (such as sucocystid cinctans, cothurnocystid stylophorans, ctenocystoids, and isorophid edrioasteroids) appeared significantly earlier in Gondwanan settings than previously thought. This shows that, even by the earliest middle Cambrian, a variety of novel body plans and ecological strategies already existed among echinoderms, pushing back the timing of important divergences into the lower Cambrian."
A Middle Cambrian echinoid - a stromatocystitid edrioasteroid (source here)
The remarkable aspect of this research is the extent of diversification reported. There are eight different body plans that indicate the animals occupied very different ecological niches. This is the ecological interpretation of the fossil record noted in previous blogs.
"There are low to medium suspension feeders (such as gogiids, lichenoidids, or isorophid edrioasteroids) that lived permanently attached; others are free-living forms, such as cinctans, stylophorans, and "eocystitids". Both gogiids and isorophids were commonly attached to skeletal debris. Previous lichenoidids known rested on the substrate, but the new specimens from Spain were also attached to skeletal debris. Cinctans and stylophorans rested on the seafloor and captured particles from the water-sediment interface."
Whatever else is understood from these data, diversification must have been earlier than previously thought. This puts the spotlight on the Early Cambrian - not just providing us with the Cambrian Explosion of animal phyla, but also the emergence of a diversity of ecosystems and the radiation of animal groups.
"Because many of these taxa appear close to the beginning of the middle Cambrian, it seems likely that their origins must be placed in the early Cambrian."
It should be remembered that the sea urchin, an echinoderm, is one of the animals whose genomes has been sequenced. Two of these genes, pax and BOULE, have been the subject of previous comment (here). Those involved with the sequencing expressed surprise at finding such sophistication, for it was realised that much of the animals genetic makeup is remarkably similar to that possessed by humans. This early appearance of genetic complexity is a major aspect of the Cambrian Explosion - for these animals were not simple or primitive in their genetic makeup. Such a flowering of biological information is inconsistent with the gradualism inherent in darwinian mechanisms.
"Any snorkeler who has ever marvelled at the spherical, almost otherworldly, symmetry of the sea urchin will be amazed to learn that this organism, so different in habitat and body plan from ourselves, actually shares a substantial number of the same genes and pathways," said Francis Collins, director of the National Human Genome Research Institute (NHGRI) which helped fund the project.
"It turns out that the sea urchin is very much like us," said George Weinstock, the co- director of the HGSC. "You wouldn't think it to look at it. But it's closer to us than a fly," he said. (Source here)
Middle Cambrian echinoderms from north Spain show echinoderms diversified earlier in Gondwana
Geology, June 2010, 38(6), 507-510 | doi:10.1130/G30657.1
Abstract: New fossil discoveries in the middle Cambrian of Spain have considerably expanded our knowledge of the temporal and spatial distribution of some major clades of echinoderms including sucocystid cinctans, isorophid edrioasteroids, cothurnocystid stylophorans, ctenocystoids, and a new group of blastozoans ("eocystitids"). Because many of these taxa appear close to the beginning of the middle Cambrian, it seems likely that their origins must be placed in the early Cambrian. These results, based on articulated specimens provided from Echinoderm Lagerstatten, agree with the hidden diversity provided from isolated ossicles from other Gondwanan areas.
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