What Did the Oldest Living Creature on Earth Look Like? Scientists Confirm the Earliest Animals That Emerged 700 Million Years Ago

Scientists have confirmed that the oldest living animal on Earth, which shares ancestry with humans, is a jellyfish-like creature called a ctenophore. These organisms emerged 700 million years ago, predating dinosaurs by 230 million years. Today, they can be found thriving in modern oceans and aquariums.

The study, titled "Ancient Gene Linkages Support Ctenophores as Sister To Other Animals" published in the journal Nature, unravels the relationships within the animal tree of life and sheds light on origins and evolution. The findings have dispelled the long-standing debate regarding sea sponges as the earliest animals, as their fossils date back only about 600 million years.

Jellyfish-Like Creature Is the Oldest Living Creature on Earth

Ctenophores are jellyfish-like creatures with eight sets of cilia for propulsion. Now, they have been identified as the oldest living animals on Earth by researchers from the University of California, Berkeley, who studied the genomes of these soft-bodied organisms to gain insights into the common ancestors of animals as their direct fossil record is lacking.

As per the press release via Berkeley News, although the study challenges the belief that sea sponges were the first animals, it instead positions ctenophores as the closest relatives to the earliest animals. The study explores the origins and evolutionary processes that gave rise to the wide array of animal species present today.

The team compared the evolutionary relationships among various animals, such as worms, flies, mollusks, sea stars, and vertebrates, collectively known as bilaterians. While bilaterians exhibit features like a centralized brain, a gut, and muscles, jellyfish lack these characteristics but share fundamental aspects of animal life.

The order in which lineages branched off from the animal tree of life has been a subject of debate, with sponges traditionally considered the earliest surviving branch. However, the absence of nervous systems and muscles in sponges challenges this view.

Daniel Rokhsar, a professor at the University of California and co-author of the study, explains that ctenophores provide valuable insights into a deep evolutionary time when direct fossil evidence is scarce. The research highlights the significance of genome comparisons in unraveling the mysteries of early animal ancestors.

Slow Evolution Allowed Scientists to Reconstruct Chromosomes of Common Ancestors

MailOnline reported that the findings show that the chromosomes of various animals evolve slowly, which enabled them to reconstruct the chromosomes of the common ancestor of these diverse animals through computational methods.

Initially, it was unclear whether the differences observed in ctenophore chromosomes were a result of gradual changes over millions of years or if they represented an ancestral state predating other animal lineages.

To resolve this, the scientists conducted genome sequencing of additional organisms, including a comb jelly, sponge, and three non-animal species: a choanoflagellate, a filasterean amoeba, and an ichthyosporean fish parasite.

Researchers found specific gene-chromosome combinations shared between ctenophores and non-animal species, while the chromosomes of sponges and other animals exhibited distinct rearrangements. The findings strongly suggested that ctenophores diverged from the common ancestor before the occurrence of these chromosomal rearrangements.

Professor Rokhsar noted that this shared gene-chromosome arrangement between ctenophores and non-animals served as compelling evidence, indicating their early branching off from the ancestral lineage, while the differences observed in other animals, including sponges, suggested distinct evolutionary events.

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