Earth’s first animal was the ocean-drifting comb jelly, not the simple sponge, according to a new find that has shocked scientists who didn’t imagine the earliest critter could be so complex.
What’s wrong with this? Basically, the study showed that the line leading to the ctenophores may have diverged before the other metazoan lineages. Stating comb jellies were the “first animal” is going to lead to people thinking that all animals evolved from comb jellies! Some other stories on this article do specify the ctenophore lineage diverged first, which is somewhat less misleading. However, this lineage diverging first does not mean modern ctenophores were there at the time. We might also consider that at that divergence the other lineage produced led eventually to humans, and we certainly were not swimming about in the ocean with the ctenophores waiting for land-living plants and animals to evolve so we could get out and dry off. Modern humans are much different from their early ancestors, and modern ctenophores may be as well.
There are several possible outcomes to this phylogenetic study. First, the findings may have been in error. Many groups are only represented in the study by one or two examples, and the sponges are one of the poorly-represented groups. Secondly, the findings may be accurate, but the ctenophore ancestors may have been quite unlike their modern form at the time they diverged and may have independently evolved their complex characteristics. Thirdly, this may mean after all that sponges have secondarily lost some complex features possessed by their ancestors. This study represents a stride forward in metazoan phylogenetics, but there is still much more to learn!
Not long after publishing my post on the improved metazoan tree of life I reviewed T. Ryan Gregory’s paper on understanding evolutionary trees. He is likewise vexed by the poor news coverage of this discovery and writes about the phylogenetic fallacy of thinking that early branching equals primitive.
If you have a strong stomach and feel up to more mangling of science, you can visit this page and find the statement that the humble opossum descended from Smilodon. The author seems to have absorbed some knowlege of the existence of non-feline saber-tooths along the way, but thinks that Smilodon was not a feline, but a marsupial. The saber-toothed marsupial he’s probably really thinking of is Thylacosmilus. In addition to this major error, the author also makes the mistake of thinking modern species are on a line of descent from extinct species that were simply in the same clade, and certainly not direct ancestors. File that under “a little knowledge is a dangerous thing”!