The living coelacanth Latimeria is an iconic ‘living fossil’ within one of the most apparently conservative groups of vertebrates. Now, paleontologists have described a new species of primitive coelacanth from a fossil found in the Late Devonian Gogo Formation in Western Australia. Named Ngamugawi wirngarri, the 375-million-year-old fossil fish fills a critical transitional stage in coelacanth disparity and evolution.
Life reconstruction of Ngamugawi wirngarri. Image credit: Katrina Kenny.
Coelacanths are evolutionarily unique lobe-finned fishes that first appeared in the fossil record in the Early Devonian epoch, around 419 million years ago.
Over 175 fossil coelacanth species are known from throughout the Paleozoic and Mesozoic eras.
During the Mesozoic, they diversified significantly, with some species developing unusual body shapes.
However, at the end of the Cretaceous period, around 66 million years ago, they mysteriously disappeared from the fossil record.
The end-Cretaceous extinction, sparked by the impact from a massive asteroid, wiped out approximately 75% of all life on Earth, including all of the non-avian dinosaurs.
Thus, it was presumed that the coelacanth fishes had been swept up as a casualty of the same mass extinction event.
But in 1938, the first specimen of the living species Latimeria chalumnae was caught fortuitously in South Africa.
The second known living species, Latimeria menadoensis, inhabits the waters off Sulawesi, Indonesia.
The specimen of Ngamugawi wirngarri. Image credit: John A. Long.
“Our study challenges the idea that surviving coelacanths are the oldest ‘living fossils’,” said University of Quebec vertebrate paleontologist Professor Richard Cloutier.
“They first appear in the geological record more than 410 million years ago, with fragmentary fossils known from places like China and Australia.”
“However, most of the early forms remain poorly known, making Ngamugawi wirngarri the best known Devonian coelacanth.”
“As we slowly fill in the gaps, we can start to understand how living coelacanth species of Latimeria, which commonly are considered to be ‘living fossils,’ actually are continuing to evolve and might not deserve such an enigmatic title.”
The specimen of Ngamugawi wirngarri was found in the Late Devonian Gogo Formation on Gooniyandi Country in the Kimberley region of northern Western Australia.
While now covered in dry rocky outcrops, this formation was part of an ancient tropical reef teeming with more than 50 species of fish about 380 million years ago.
Phylogenetic relationships and divergence dates within coelacanths. Image credit: Clement et al., doi: 10.1038/s41467-024-51238-4.
“Ngamugawi wirngarri provides us with some great insight into the early anatomy of this lineage that eventually led to humans,” said Flinders University’s Professor John Long.
“For more than 35 years, we found several perfectly preserved 3D fish fossils from Gogo sites which have yielded many significant discoveries, including mineralized soft tissues and the origins of complex sexual reproduction in vertebrates.”
“Our study of this new species led us to analyze the evolutionary history of all known coelacanths.”
“We calculated the rates of evolution across their 410 million-year history,” they said.
“This revealed that coelacanth evolution has slowed down drastically since the time of the dinosaurs, but with a few intriguing exceptions.”
The findings appear in the journal Nature Communications.
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Alice M. Clement et al. A Late Devonian coelacanth reconfigures actinistian phylogeny, disparity, and evolutionary dynamics. Nature Communications, in press; doi: 10.1038/s41467-024-51238-4