Everyone from paleontologists to cartoonists has expanded on the hotly debated idea that life on earth began in the sea. But what about the fish themselves? According to an October 2018 study, vertebrate fish originated in shallow-water environments in the mid-Paleozoic era.
This unexpected finding refuted the scientific community’s common ideas that fish evolution took place in the deep blue sea or even on coral reefs.
But the research indicated prehistoric fish evolved much nearer to shore. Few had jaws, many of them were armored and had spikes and others looked like clams with tails. Still, according to this data compiled from early fish fossil records, all these prehistoric fish originated in shallow coasts quite near to supercontinents.
These aquatic vertebrates are the earliest human ancestors with spines. New information about their origins changes existing scientific thought and paves the way for new findings on the origins of life on earth.
Tracking Fish In Scientific Literature
To arrive at their conclusion, researchers compiled a database reconstructing vertebrate fish habitats from 490 million to 360 million years ago.
They combed global scientific literature, which yielded 2,700 applicable fossil records from that timespan.
Researchers then assessed the date, revealing fish vertebrate descendants that evolved from a common ancestor (known to scientists as a “clade”) in this roughly 130 million-year timeline all came from restricted, shallow-water environments.
The typical evolution habitat was no deeper than 100 feet, according to the database. Previous theories had fish moving from deep water to shallow and then to shore as vertebrates evolved.
This new research indicates that after fish evolved in the shallows, the stronger swimmers left for deeper types of water, including reefs and the sea.
Extinct Fish Looked Very Different Back Then
The team studied fossil records from fish quite different than the modern tilapia and salmon of today.
In the mid-Paleozoic era when fish were evolving, some, like arandaspids, sported plates of armor and had no jaws. Other varieties looked like underwater armadillos or had horseshoe-shaped heads.
In the intervening millions of years, some of these hulking plated fish became bottom feeders. They may have been the ancestors of the fish that eventually moved along to freshwater, including streams and lakes.
Prehistoric placoderms were considered the first fish with jaws. Though they had no teeth, their razor-sharp mouth edges and giant maws helped them dominate the environment.
They outlasted the time frame the researchers studied, persisting into the Carboniferous Period that began about 359.2 million years ago.
However, they were short-lived compared to sharks, which evolved around the same time and still thrive today.
More Research To Come
The team that established the early fish evolved in shallow waters isn’t precisely sure why it happened that way.
Their theories include factors involving sea level changes, runoff and rainfall. Other thinking includes the impact of water chemistry and possibly oxygen levels in the ancestral habitats where prehistoric fish evolved.
As further research fills in the picture, scientists hope it will also link to expanded answers on how amphibians and other land vertebrates evolved.