These ancient fish lineages survived mass extinctions, ice ages, and evolutionary upheaval.
Earth’s biological history stretches far beyond the age of dinosaurs. Hundreds of millions of years ago, prehistoric seas and rivers were full of strange fish with armor, fins, lungs, slime, and jawless mouths. Most of those ancient lineages disappeared during mass extinctions. A few, however, survived.
Today, scientists often call them “living fossils.” It’s a catchy phrase, but it’s not entirely accurate. These six ancient fish lineages aren’t exactly unchanged, because evolution never really stops. But they retain body plans, lifestyles, or genetic features that reach astonishingly far back in evolutionary history. This makes them scientific treasures.
But how did they survive dramatic shifts in climate, and what can they teach us about our own biology? Recent genomic breakthroughs and anatomical studies reveal that these ancient survivors hold the secrets to the evolution of limbs, lungs, and even human brains.
The earliest definitive dinosaurs appear in rocks about 230 million years old. The fish lineages listed below go back far deeper.
1. Coelacanth
The coelacanth is arguably the most famous living fossil. Scientists believed this deep-sea fish vanished 65 million years ago until a living specimen appeared off the coast of South Africa in 1938. It was one of the great zoological surprises of the 20th century.
Coelacanths belong to an ancient group of lobe-finned fishes that dates back roughly 400 million years. Their fleshy, limb-like fins once made them look like a possible stepping stone in the transition from water to land. Later genetic studies showed that lungfish, not coelacanths, are our closest living fish relatives.
This genetic investigation also confirmed what many scientists had long suspected: genes in coelacanths are evolving more slowly than in other organisms.
“We found that the genes overall are evolving significantly more slowly in the coelacanth than in every other fish and land vertebrate that we looked at,” Jessica Alföldi, a Broad Institute researcher and co-first author of a Nature genome paper, told the Wellcome Sanger Institute.
Recent research has made the fish stranger still. A 2021 study of growth marks in coelacanth scales found that African coelacanths may live for about a century and carry young for roughly five years, an extraordinarily slow life history that makes them especially vulnerable to fishing pressure.
2. Sturgeon
Sturgeons are massive, bottom-feeding fish armored with bony plates. Their lineage reaches back more than 200 million years, and researchers often describe them as the “Methuselah of freshwater fish.” Because of their minimal physical evolution, they still strongly resemble their fossilized ancestors.
In 2020, scientists sequenced the sterlet sturgeon genome and found that the fish had duplicated its entire genome about 180 million years ago, leaving it with four sets of chromosomes. Yet its protein evolution remained slow, comparable to coelacanths and sharks.
“Sturgeon genomes are an important piece of the puzzle that helps us understand the ancestry of vertebrates. And this has been missing until now,” Manfred Schartl of the University of Würzburg said in a university release.
Most sturgeon species are now threatened by habitat loss, dams, pollution and the caviar trade.
3. Lungfish
Lungfish are amazing for many different reasons. Number one, they’re fish that breathe air. Secondly, they are among our closest living fish relatives.
Lungfish belong to the lobe-finned fishes, the same broad group that eventually gave rise to four-limbed vertebrates. Modern lungfish can gulp air using lungs, survive oxygen-poor waters, and, in some species, endure drought by slowing their metabolism inside mud cocoons.
In 2021, researchers published a chromosome-quality genome for the Australian lungfish, then known as the largest animal genome sequenced at the time. In 2024, a broader study of all lungfish genomes reported that the South American lungfish has about 91 billion DNA bases — roughly 30 times the human genome and the largest animal genome sequenced so far.
Decoding this massive genome helps geneticists understand the molecular shifts that allowed our ancestors to crawl onto land.
4. Lamprey
Lampreys look like something from a nightmare. They don’t even look like fish, but they are.
These jawless, eel-like fish have circular mouths lined with teeth. Some species use them as suction cups, latching onto other fish and feeding on their blood and body fluids. Their lineage has persisted for more than 340 million years. Lampreys split from the line that led to jawed vertebrates before jaws, paired fins, and bony skeletons became standard equipment.
Despite their primitive anatomy, lampreys are incredibly valuable to modern medicine. Recent research reveals that the hindbrain of the sea lamprey develops using an almost identical genetic toolkit to that of humans. Furthermore, biodiversity surveys continue to uncover hidden lineages. In 2024, researchers identified two entirely new, genetically distinct populations of lampreys in California’s rivers.
“They are very genetically different from any lamprey that has ever been collected from anywhere,” says researcher Grace Auringer.
5. Hagfish
Hagfish are the deep sea’s slime specialists.
When threatened, they can release astonishing amounts of mucus, clogging a predator’s gills and buying time to escape. They have no jaws, no true vertebral column in the familiar sense, and a scavenger’s talent for finding dead animals on the seafloor.
Hagfish represent one of the earliest branches of the vertebrate family tree, originating around 500 million years ago.
For the longest time, hagfish have frustrated geneticists. Their genome was hard to assemble because it is packed with repetitive sequences and small chromosomes, some of which are lost from most cells during development. In 2024, researchers finally published major hagfish genome studies that helped clarify when ancient genome duplications occurred in early vertebrate history.
“Reconstruction of the early genomic history of vertebrates provides a valuable foundation for understanding where most of the genes in humans and other animals came from, and how genomes work in general,” said Jeramiah Smith, a professor in the Department of Biology at the University of Kentucky. “This research also further explores the evolution of vertebrates and gives us an opportunity to learn more details about our deep ancestry.”
Researchers discovered that hagfish underwent massive genomic changes over time, including chromosomal fusions and the deliberate loss of crucial genes. They found that hagfish lost genes tied to organs such as eyes and cartilage, while expanding gene families involved in slime production.
6. Paddlefish
The American paddlefish seems almost unfinished: a shark-like body, a gaping mouth and a long, blade-shaped snout.
That snout, called a rostrum, is packed with sensors that help the fish detect tiny prey in murky rivers. Paddlefish belong to Acipenseriformes, the same ancient order as sturgeons, a group estimated to have originated 300 to 350 million years ago or earlier.
Recent genome assemblies published in Molecular Biology and Evolution revealed that the American paddlefish underwent a species-specific whole-genome duplication, essentially copying their entire genetic code. By now, this shouldn’t surprise anyone as these sorts of genome duplications are shared by virtually all living fossils.
Then, in 2023, a Nature Communications study argued that paddlefish and sturgeon share an ancient whole-genome duplication that occurred more than 200 million years ago, likely near the Permian-Triassic mass extinction.
Ancient Life Endures, But Not Automatically
These fish are often called “living fossils,” but the phrase can be misleading. They are not museum pieces. Their genes change, albeit very little, and their populations rise or fall with rivers, oceans, fisheries and climate.
For instance, Chinese paddlefish was recently declared functionally extinct, leaving the American paddlefish as the last living species in its family.
These seven fish species survived asteroid impacts, brutal ice ages, and the violent splitting of continents. They swam silently in the deep while dinosaurs ruled the land, and they persisted long after those giants turned to dust. Yet, their greatest evolutionary test might be happening right now.
Unlike the gradual planetary shifts of the prehistoric past, modern environmental changes happen at breakneck speed. Human-driven climate change, massive dam construction, and rampant water pollution alter ecosystems in decades rather than millions of years. For creatures like the paddlefish and the sturgeon—whose DNA changes slower than almost any other vertebrate—adapting quickly to these sudden modern threats poses a massive challenge.
https://www.zmescience.com/feature-post/natural-sciences/animals/fish/6-ancient-fish-older-than-dinosaurs-that-are-still-swimming-today/
No comments:
Post a Comment