There’s been a bit of a jostle recently between claims made for sponges vs claims made for comb jellies as the first significant complex life. Both types of life forms are at least 500 million years old. Using a bigger data set, this group of researchers favors the sponges. From ScienceDaily:
Of particular interest among these animal phyla are the sponges (Porifera) and the comb jellies (Ctenophora), as it remains unclear which of these groups represents the sister group to all other animals. “Irrespective of whether we include paralogs or not, our results are consistent with the classical view of animal phylogeny in that the sponges are the sister group to all other extant animal lineages,” says Wörheide. Analysis of the ortholog gene content on its own places the comb jellies as the sister group of Placozoa, Cnidaria and Bilateria (this last group accounts for 95% of extant animal species). Including homologous gene family content data, however, identifies ctenophores as the sister group of the Cnidaria. This result agrees with a proposal drawn from morphological studies — the Coelenterata hypothesis — that dates back to the mid-19th century, a view which had gone out of favor in recent years.
“We conclude from our results that the anomalous placement of some highly divergent lineages, such as the comb jellies, reflects a fundamental limitation in the ability of conventional sequence-based methods — which rely on data for orthologs alone — to resolve the branching patterns of very ancient lineages,” says Wörheide. Paper. (paywall) – Walker Pett, Marcin Adamski, Maja Adamska, Warren R Francis, Michael Eitel, Davide Pisani, Gert Wörheide. The role of homology and orthology in the phylogenomic analysis of metazoan gene content. Molecular Biology and Evolution, 2019; DOI: 10.1093/molbev/msz013 More.
For various views, see
Researchers: Sponges Definitely Oldest Animals, Not “Anatomically Complex” Comb Jellies
Our physics color commentator Rob Sheldon offers an analysis:
Problem. Square peg. Round hole.
Solution. Bigger hammer.
Who says evolution has unsolved problems?
So let’s wait and see what the other side says. Chances are we haven’t heard the last of it.
Sponges vs. jellies: Comb jellies still the “oldest” complex life form, researchers say
Sponges back in the ring with comb jellies for “oldest” title fight
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Comb jelly DNA sequence offers “unintuitive facts” about evolution…
Researchers: The sponge is the oldest animal phylum after all (2015)