Living fossil fish whose evolution stopped 105 million years ago

Life on Earth is constantly being renewed — Species either evolve or go extinct. It is believed that the average lifespan of one species ranges from 500 thousand to 3 million years. Of course, we can recall creatures such as shield crabs and horseshoe crabs, which have existed for hundreds of millions of years. But, as we previously told, they are only superficially similar to their ancestors, but in fact they have also evolved greatly. However, as a recent study has shown, there are species that actually evolve very slowly, resulting in little difference from their ancestors who lived more than 100 million years ago. An example is the fish of the family Lepisosteidae, which have not changed much over the past 105 million years, and therefore can fully be called “living fossils.”

Living fossils of fish whose evolution stopped 105 million years ago. Shellfish have remained almost unchanged over the past 100 million years. Photo.What are living fossils

It has long been known that some organisms have very low species diversity and yet differ physically only slightly from their ancient ancestors. Therefore, in 1859, Darwin coined the term “living fossils.” As you might guess, this term refers to creatures that are fossils, that is, those who lived tens or hundreds of millions of years ago, and who live to this day. However, until recently, there was no clear evidence of the existence of living fossils.

To find out whether such species exist, a team of American and Chinese scientists conducted a study that used computer analysis of gene sequences in species that were considered living fossils. Using this analysis, the authors determined how many genes they had preserved from their common ancestors. In this way, they identified the rate of replacement (mutation) of genes over time. In total, they examined 1,105 coding regions of DNA from nearly 500 different species of jawed vertebrates.

What are living fossils. Coelacanth is not a living fossil. Photo.

Coelacanth is not a living fossil

The study found that some creatures previously thought to be living fossils are not actually living fossils. For example, this applies to species such as tuatara (Sphenodon punctatus), coelacanth (Latimeria chalumnae), hoatzin (Oisthocomus hoazin). All of them are very different from their fossil relatives, that is, they have evolved greatly, like the aforementioned horseshoe crabs and shield crabs. Although they did retain many common characteristics. Let us recall that, according to scientists, coelacanth looks the same as ancient fish that began to reach land 360 million years ago.

Living ancient fish

Despite the fact that most of the species did not turn out to be “living fossils,” some species developed very slowly, as a result of which, as mentioned above, they are not very different from their ancestors. We are talking about fish – pike and related sturgeon. The rate of their evolution, according to scientists, is three times lower than that of other vertebrate species. For example, the study showed that the DNA of armored pikes is practically no different from the DNA of ancestors who lived more than 100 million years ago.

Living ancient fish. Long-snouted carapace — a real living fossil. Photo.

It must be said that an indicator that a species has changed minimally is the ability of its various representatives to produce hybrid offspring. For example, horses and donkeys can interbreed and produce offspring known as mules. However, the hybrids are sterile. The last common ancestor of the horse and donkey lived 4 million years ago.

As reported in a study published in the journal Evolution, the Mississippi batfish (Atractosteus spatula) and the long-snout batfish (Lepisosteus osseus) have evolved so slowly that they are capable of interbreeding and producing hybrid offspring. Moreover, unlike horses and donkeys, their offspring are not infertile. The division between these species occurred approximately 105 million years ago. It seems that the evolution of these fish has practically stopped.

Live ancient fish. A hybrid of two species of Mississippian shellfish (Atractosteus spatula) and long-snout shellfish. Photo.

Hybrid of two species — Mississippian armor (Atractosteus spatula) and long-snouted armor

As the researchers themselves say, the ability of both species to produce hybrid offspring — this is an incredibly amazing phenomenon. In terms of the amount of time that has passed since the moment when both species separated, it is equivalent to the fact that hybrids would have been born when crossing humans and wombats.

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But why were the genes of these species so stable? Scientists have yet to answer this question. However, the secret of living fossils is believed to lie in a powerful DNA repair mechanism. All living organisms have this mechanism, but for some reason it works more efficiently in these creatures.


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