The comb jelly shows fewer chromosomal rearrangements compared with the inferred ancestral genome, suggesting it branched off earlier than the sponge and represents the earliest-diverging animal lineage.

This result settles a long-standing question about the root of the animal family tree and opens new avenues for studying the mechanisms and history of animal evolution.

Researchers compared the chromosomes of sponges and comb jellies to those of their closest single-cell non-animal relatives to reconstruct the ancestral genome and measure rearrangements since divergence.

Based on chromosomal arrangement, the comb jelly is identified as the sister lineage to all other animals, marking the first major split in the animal tree of life.

For decades, scientists debated whether sea sponges or comb jellies were the earliest diverging lineage, now clarified by methods focusing on chromosome placement rather than gene content alone.