Biologists have been searching for the oldest animals for over a century, narrowing the options down to two groups sponges and comb jellies. Sponges spend their entire adult life filtering food through salt water; and scallop jellies, ferocious hunters who row the world's oceans in search of food. Ctenophores are the first lineage to branch from the animal tree, according to a new study. Then came the sponges, then diversified all other animals, including human origin. Although the ctenophore lineage diverged before the sponges, both groups of animals continued to expand from their common ancestor. However, evolutionist scientists think that these groupings still share the same characteristics as the oldest animals, and studying the life branches of these early animal trees will help us understand how animals emerged and evolved into the various species we see today. "The most recent common ancestor of all animals probably lived 600 or 700 million years ago. It's hard to know what they looked like as they were soft-bo animals and didn't leave direct fossil records. But we can use comparisons between living animals to learn about our common ancestors." said Daniel Rokhsar, professor of molecular and cell biology at the University of California, Berkeley and co-author of the paper, along with Darrin Schultz and Oleg Simakov of the University of Vienna. "This is exciting - we're looking into the past where we had no hope of finding fossils, but by comparing genomes, we learn about these very early ancestors," said the researcher. Understanding the relationships between animal lineages will help scientists understand how key features of animal biology, such as the nervous system, muscles, and digestive system, evolved. We have developed a new way to take one of the deepest possible insights into the origins of animal life.” Schultz, a researcher at the Monterey Bay Aquarium Research Institute , is lead author and a former UC Santa Cruz graduate student and now a postdoctoral fellow at the University of Vienna. This finding will lay the foundation for the scientific community to develop a better understanding of how animals evolve. Most familiar animals, including worms, flies, mollusks, sea stars, and vertebrates, including humans, have a central brain, a gut extending from the mouth to the anus, muscles, and other common features that evolved in the time of the vowels. Cambrian Explosion 500 million years ago. These animals are known together as bilaterians. "Traditionally, sponges are thought to be the oldest surviving branch of the animal tree because sponges have no nervous systems, no muscles, and look a bit like colonial versions of the unicellular protozoans, and it was a good story First came the unicellular protozoans, then spongy cells of this type." The multicellular consortium evolved and became the ancestor of all modern-day animal diversity. In this scenario, the sponge lineage retains many of the features of its animal ancestor in the clade that gave rise to all other animals, including ourselves. They have neurons, nerves, muscles, guts, and what we know and love as defining features of the rest of animal life. "The specialties that led to everything have evolved. Sponges look primitive because they lack these properties." DNA sequencing was used to construct a family tree. However, he could not settle the debate over whether the oldest branches of the animal tree were sponges or comb jellies. The results of sophisticated sequence-based studies were split. Some researchers did well-designed analyzes and found that sponges branched out first. Others did equally complex and defensible studies and took ctenophore. There has been no convergence to a definitive answer.” In 2019, a bioluminescent deep-sea sponge was discovered. Because sponges lack nerves and muscles, they have historically been considered the oldest surviving branch of the animal tree. Jellyfish, sea anemones, sponges, and ctenophores lack many binary features, but share distinctive features of animal existence. The evolutionary relationships between these different creatures have been controversial because their differences are so ancient. A new study has discovered that honeycomb jellyfish and ctenophores are also possibilities for the oldest animal lineage. This is because genes are structured into chromosomes, each species has a unique chromosome number and gene distribution along the chromosomes. This suggests that the first animals came from single-celled protists billions of years ago. The other candidate for the oldest animal lineage is the honeycomb jellyfish group, which are popular animals in many aquariums. At the same time, they superficially resemble jellyfish - they often have a bell-like shape, but unlike jellyfish with two lobes and often tentacles - they are only distantly related. As the jellyfish sprout out of the water, the ctenophores propel themselves with eight rows of whisker cilia arranged like combs next to them. The 1-inch diameter sea gooseberry is a common ctenophore on the California coast. The new study relied on an unusual feature to determine whether sponges or ctenophores were the oldest branch of animals the arrangement of genes into chromosomes. Each species has a different chromosome number - humans have 23 pairs - and there is another distribution of genes along the chromosomes. Rokhsar, Simakov and others had previously shown that the chromosomes of many invertebrates contain comparable gene sequences. However, the chromosome structure of ctenophores was unknown until 2021, when Schultz and his co-advisors determined the chromosome structure of Hormiphora californensis. This showed that ctenophores and non-animals share specific gene-chromosome combinations, whereas the chromosomes of sponges and other animals are rearranged differently. Bolinopsis microptera is a ctenophore that shares rearrangements with non-ctenophore animals. This suggests that ctenophores diverged before rearrangements and are still present in animal genomes hundreds of millions of years later. This work is funded by the David and Lucile Packard Foundation. Journal Reference