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You walk, talk and live on earth, but your former parents were fish.
It took about 480 million years for these fish to evolve and adapt to different environments and become the many different species (including ourselves) with boneless ridges, known as vertebrates.
But how did it happen?
The field of paleontology looks at when or and Why animals evolving with time and according to their environment. Today, Lauren Sallan of the University of Pennsylvania (along with other American and British colleagues) responds to "or" question about our ancestors more distant fish.
For the first time, the work shows that shallow coastal lagoons were vital in the early days of fish evolution. Nowadays, similar seas ("plateau seas") encompass places such as Bass Strait, where water is formed within 200 m of depth around a continental shelf.
These places are still important today to maintain the biodiversity of life on Earth – so if we do not take care of our shallow oceans, the long-term consequences for marine life could be disastrous.
The ancient fish lived, evolved and died in a relatively shallow sea near the land, similar to today's strait between Tasmania and Victoria. from www.shutterstock.com
Invasion of the ocean
To conduct their research, scientists used a database of 2,827 species of fossil vertebrates. These covered the 120 million years that preceded the appearance of fish (about 480 million years ago) until their conquest of the territory as creatures to four branches known as tetrapods (about 360 million years ago). The database has mapped the habitats of species according to their time ranges and has identified important steps in the formation of new species (known as diversification).
The research points out that littoral coastal environments, including estuarine and lagoon environments, were hotspots for major episodes of early vertebrate diversification – not open oceans where we might think that fish would naturally undergo evolutionary events.
Robust body fish (such as finfish species such as fish-lungs) then searched for habitats closer to the land to diversify, while small-scale thin forms such as jawless thelodontids (such as yellow fish in the picture below) and some sharks to go deeper waters.
Lead researcher Lauren Sallan said:
This research establishes an "invasion of the ocean" on par with the land invasion. Our early ancestors moved quickly into fresh waters, but their passage over the reefs and from there to the ocean and new continents took a lot of time and change.
A thelodont without jaws like an angel forms among jellyfish in the shallow waters 415 million years ago (artist impression). Nobumichi Tamura]
Fish with and without jaws
The first diversification of the first jawless fish (resembling the lamprey and hagfish today) led to the appearance of many groups of armored fish at the beginning of the Silurian period (about 420 million years ago). The armored fish had hard plaques on the body and most lived in the shallow inland seas of the continents of the Northern Hemisphere.
The oldest fossil of jawless fish comes from Australia, as represented by simple torpedo-like shapes, such as Arandaspis who lived in the shallow seaway of Larapintine across Australia about 470 million years ago.
The first large ray of jaw fish (called "gnathostomes") occurred in China about 440 million years ago. At the beginning of the Devonian period (419 million years ago), all major groups of jaw – fish had appeared and dispersed in all regions of the world.
Other fish have evolved in distinct regions, such as the East Gondwana Province (Australia and Antarctica) and in the Euramerica supercontinent (a continental mass combining much of North America and North America). from Europe).
The animals called "the Wuttagoonaspis The fauna "included many strange forms of placoderm and other primitive fish, and is the oldest local group of vertebrates in Australia. The remains of these distinctive fish that lived about 395 million years ago are found in many sites in an area of two million square kilometers in central Australia.
Devonian reef scene showing ancient bony fish (foreground) and armored placoderms behind. Reefs do not seem to play an important role in the early diversification of fish (impression of the artist). Brian Choo, Flinders University (with permission), author provided
The historic reefs were different
Reefs are well known for being hot spots of biodiversity – today, several thousand species of fish live around coral reefs. But we now know that this is not always the case.
Prehistoric reefs, known for about 500 million years, have been built by different organisms over time. Devonian reefs, home to many species of fish, were mainly constructed of algae and sponges, with a smaller contribution from corals.
The Devonian Kimberley reefs were home to more than 50 species of ancient fish living on algal structures lining most of northwestern Australia.
But new research shows that the Silurian and Devonian reefs did not exhibit unusually high diversity, as previously assumed. This suggests that reefs played a much less important role than we thought in the early rise of jawed fish.
A jaw placoderm dating from the Devonian period, but resembling a modern stingray, rests near the edge of the plateau in Germany (impression of the artist). Nobumichi Tamura
Take care of our shallow waters
The message of the new document is that the cradle of first vertebrate diversification has occurred mainly in shallow water habitats close to or across a continent's borders.
The steady rise and fall of sea level over time would have had a significant effect on the habitat size of these marine species, making them particularly vulnerable to extinction when communities lived in basins with low oxygen levels.
These extinctions involved many factors and eliminated some of the dominant fish groups at the end of the Devonian, including placoderms. This has allowed modern fish groups, consisting mainly of bony fish and sharks, to establish themselves.
The research has some implications for today, as one of the authors of the paper, Ivan Sansom of the University of Birmingham, explained:
This work highlights the importance of these increasingly vulnerable coastal areas for species evolution. Modern threats resulting from a combination of climate change, sea level rise, overfishing and pollution could have extremely damaging effects on the future diversification of species.
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