“Living Fossil” Discovered by Accident Could Reshape Tree of Life

Explore

IIt is not uncommon for a new species to be discovered among existing collections; However, it is rare that the new species is still alive. But that’s what a research team from Charles University in the Czech Republic discovered when examining an ancient culture of marine microorganisms.

In the years-old sample, larger organisms had expired, but one small, strange-looking creature still remained. It was a tiny single-celled protist, a catch-all group of eukaryotic organisms that are neither plants, animals nor fungi. With ray-like protrusions extending from a central mass, their new discovery resembled a sun, which is why the team nicknamed it Solarion arianaepublishing their findings in Nature.

The curious structure and resilience of this new species were remarkable, but genetic analysis revealed S. arianae hid even more astonishing surprises. After sequencing the genome and cross-referencing it with existing databases, the researchers determined that this organism did not belong to any previously recognized lineage of eukaryotes. Instead, S. arianaealong with a handful of other mysterious protist relatives, formed a new supergroup, called Disparia. A search of environmental DNA databases indicated S. arianae is (somewhat paradoxically) both rare and widespread, living a quiet life in marine sediments.

The DNA inside was even more surprising S. arianae mitochondria. Nestled within these organelles was the gene secAa fragment of a protein translocation system inherited from the bacterial ancestor that gave rise to mitochondria, and a sequence lost in almost all other eukaryotic species. According to endosymbiotic theory, mitochondria were once free-living prokaryotic cells that were engulfed by eukaryotic cell precursors. After this intimate interaction, the eukaryotic cells housed the mitochondria, which provided energy for the partnership and resulted in the profusion of eukaryotes we see today.

Read more: »The unique fusion that made you (and sheep and yew)»

In other words, S. arianae is essentially a living fossil, allowing researchers unprecedented insight into the evolution of eukaryotic life.

“Solarion is a remarkable reminder of how little we still know about the diversity of microbial life,” study authors Ivan Čepička and Marek Valt said in a statement. “The discovery of such an evolutionarily deep lineage – essentially a living fossil – shows that key elements of eukaryotic history remain hidden in places we rarely explore.”

Scientific breakthroughs that change the tree of life: always at the last place you look.

Enjoy Nautilus? Subscribe for free to our newsletter.

Main image: Charles University

• Jake Currie

  Published on November 20, 2025

  Jake Currie is a writer based in Brooklyn, New York.