Contemporary coelacanths are often described as living fossils. Superficially, that may be true. But new evidence now makes that nickname less valid.
The two species of the large-boned lungfish alive today don’t look that much different than the first known coelacanth fossil dating back over 410 million years ago. But two new fossils show that the species did evolve — albeit slowly and subtly. Also, scientists for the first time link evolution to tectonic activity, according to a report in Nature Communications.
Coelacanth Fossils Discovered in Australia
There is much to unpack in the significance of the study. First, it describes a new species of coelacanth.
“That, in itself is a big deal,” says Richard Cloutier, a professor with University of Quebec in Rimouski (UQAR) and an author on the paper. A team led by Flinders University in Australia and included experts from Canada, Australia and Europe, found the two fossilized fish, which they named Ngamugawi wirngarri, in Western Australia.
The time period from which the fossils came from also make them, in many ways, pivotal fish. They hail from the Devonian Period (359 million years to 419 million years ago), which represents a hinge where evolution differentiates the oldest known coelacanths with their two remaining living relatives.
“The new species fits just between the two big evolutionary periods of the coelacanth,” says Cloutier.
Read More: Take a Tour of These Incredible Living Fossils
Tectonic Activity in the Devonian Period
The Devonian also saw a massive amount of tectonic activity, which reshaped coastlines, created islands, and, in general, provided pretty substantial habitat change for ocean dwellers. That activity also led to substantial ocean extinctions.
And, as a bonus, the two specimens were in great shape. Many coelacanth fossils are found flattened, shattered, and incomplete.
“These are preserved in 3D, which permits us to look at the internal anatomy of the skull,” says Cloutier. “We were able to reconstruct the brain. It is kind of kind of amazing to be able to reconstruct the brain of an animal that was living 380 million years ago.”
Read More: Marine Life Perished From the Late Devonian Mass Extinction
Evolutionary Finds About Coelacanths
The quality of those fossils allowed the scientists to compare 300 or so physical characteristics in about 80 coelacanth species. The first such exercise in this prehistoric fish illustrated the number of subtle, but important shifts the coelacanths underwent over 400 million years or more. They could also observe what changes occurred during the Devonian Period.
The team’s comparisons revealed many evolutionary tweaks. For instance, skull proportions altered over millions of years. So did fin placement, and a host of other characteristics. Taken alone, each difference might seem marginal. But collectively, and over time, they provide an example of a species well adapted to its environment that, nevertheless, slowly evolved over time.
But, especially after the Devonian Period, their essential shape hasn’t changed much — which suggests that evolution matched their body with a relatively stable living environment.
“Their body shape was fine 300 million years ago. Their body shape was fine 100 million years ago and is fine today,” says Cloutier.
The team would next like to see how the tectonic activity during the Devonian Period might have affected evolution of other creatures. Sharks are a possible candidate to study that effect.
Read More: The Hidden Evolution of These 4 Ancient Living Fossils
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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
