Ancient fish fossils found, early jawed vertebrates

un antico fossile di pesce con la mascella

In southern China, strange fossils have been found that are a real window on history of all vertebrates, including us humans. Their peculiarity immediately catches the eye: they are small fish with bones and teeth never seen before and dating back between 439 million and 436 million years ago. With diversity and characteristics that until now had only been hypothesized by scholars, but of which we finally have tangible and observable proofs.

A sensational discovery on the first vertebrates

The study published in Nature it is truly sensational and immediately attracted the attention of everyone, professionals and others. Because they have always explained and taught us that evolution has led some fish to develop characteristics that have them as invertebrates “transformed” into vertebrates, but it had not been possible to observe or study so far such large and complete remains that they actually proved it. At least not like those found in the southern Chinese site whose origin dates back to more than 400 million years ago.

The genetic analysis of these fossils allowed paleobiologists to date the site (called Chongqing Lagerst├Ątte) with great accuracy, thus tracing it back to the so-called early Silurian period, just the one in which there has been a rapid diversification of vertebrates. “These findings confirm what we have been arguing about” for years based on very small fossil fragments, said University of Chicago paleobiologist Michael Coates.

We knew that the toothed fish populated the waters at that time, but it seemed they had not left enough traces (therefore fossil finds) to explain both its origin and its diversification. It is therefore easy to understand why this last study is so important: elements are added that are like the missing link in this pregnant part of the history of living creatures. The same ones that, then, gave rise to the species we know, including us.

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Because ancient fish developed jaws

Paleontologist You-an Zhu of the Chinese Academy of Sciences in Beijing and colleagues who collaborated on the study are nothing short of thrilled with the discovery. This rich group of fossils features specimens of different species, all toothy and bony fish, most notably the armored placoderms and a chondrictian. They are essentially the creatures that first developed the backbone about 480 million years ago, and then developed the jaws as well. The reason? A simple one question of survival: they could eat each other better.

Thus we find the Xiushanosteus mirabilis, a tiny staple-sized fish and ancestor of armored fish, with a broad shield covering its bony head and body covered with tiny hard scales. Or again the Shenacanthus vermiformisalso tiny (just 22 mm) and with bones and cartilages, in addition of course to the jaw.

Genetic analysis would also demonstrate another important thing. Most likely the last common ancestor of modern maxillary vertebrates could be even older than we think, datable to the Great Ordovician Biodiversification Event, that is to say about 471 million years ago. The rest is history: over time the fish with the jaw have become a real global phenomenon, so much so that the Devonian period (between 419 million and 359 million years ago), that of their domination, has earned the nickname of “Age of Pisces”.

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