This is a complex and long-running dispute. From ScienceDaily:
Commenting on the breakthrough research, Professor Pisani said:
“The fact is, hypotheses about whether sponges or comb jellies came first suggest entirely different evolutionary histories for key animal organ systems like the nervous and the digestive systems. Therefore, knowing the correct branching order at the root of the animal tree is fundamental to understanding our own evolution, and the origin of key features of the animal anatomy.”
In the new study, Professor Pisani and colleagues used cutting edge statistical techniques (Posterior Predictive Analyses) to test whether the evolutionary models routinely used in phylogenetics can adequately describe the genomic datasets used to study early animal evolution. They found that, for the same dataset, models that can better describe the data favour sponges at the root of the animal tree, while models that drastically fail to describe the data favour the comb jellies.
Dr Feuda from Caltech continued: “Our results offer a simple explanation to the ‘flip-flop effect’ cogently discussed by Professor David Hillis in a recent interview in Nature.”
Dr Dohrmann from LMU added: “Our results rationalise this effect and illustrate how you can draw robust conclusions from flip-flopping dataset.”
Professor Gert Wörheide of LMU said: “Indeed, a flip-flopping dataset is a dataset that supports different evolutionary histories or phylogenetic trees, when analysed using different evolutionary models.
Discriminating between alternative hypotheses in the face of a flip-flopping dataset requires clarifying how good the models are that support alternative phylogenetic trees. Posterior Predictive Analyses allow us to do exactly that. We found that models which describe the data poorly invariably identify the comb jellies at the root of the tree. Models that better describe the data invariably find the sponges in that position.” Paper. (public access) – Roberto Feuda, Martin Dohrmann, Walker Pett, Hervé Philippe, Omar Rota-Stabelli, Nicolas Lartillot, Gert Wörheide, Davide Pisani. Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals. Current Biology, 2017; DOI: 10.1016/j.cub.2017.11.008 More.
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.
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
Comb jelly files: Complex features do not each emerge once
Comb jelly DNA sequence offers “unintuitive facts” about evolution…
and
Researchers: The sponge is the oldest animal phylum after all (2015)