The Ichthyostega was a genus of prehistoric animal that inhabited our planet during what we know today as the Paleozoic Era, specifically in the Devonian period (about 360 million years ago).
This genus has been classified within the group of the tetrapods.
This animal inhabited our planet long before the dinosaurs themselves and is one of the oldest animals for which there is evidence. This animal would have been a key point in the history of evolution, since it is one of the first quadruped vertebrates.
At the moment, with the records that we have, it would have been without a doubt the first animal to set foot on solid ground. The life of living beings in its time was completely developed in the sea.
If you want to know more about the Ichthyostega, read on and discover everything about this fascinating animal!
What does the name Ichthyostega mean?
The meaning of the name is “Fish with a roof”, a name that comes from the Greek “στέγη” (stégi) which is understood as “roof” and the Greek “Ιχθύες” (Ichthýes) which is understood as “fish”.
History of the discovery
The first fossil remains of this amphibian were found in 1929 and in 1931, in a series of expeditions led by the Danish geologist and explorer Lauge Koch, up to 14 specimens were found.
Other discoveries of this animal took place in Greenland, in 1932; and on this occasion it would be the researcher Gunnar Söderberg-Seva who would describe these fossils. He is also the one who gave the name of Ichthyostega; and who also reached the conclusion that there were at least 4 species which he called: I. stensioei, I. watsoni, I. eigili and I. kochi.
Although a more recent study would assume that this genus is only represented by the species I. stensioei because the other species had significant morphological differences.
Despite the large amount of fossil evidence, none of them was sufficiently complete. Nevertheless, the Museum of Natural History in Stockholm gathered all the fossils found and made the first reconstruction of the Ichthyostega in 1955, which was carried out by the paleontologist Erik Jarvik and whose illustration shows the Ichthyostega with an appearance very similar to that of a crocodile, although he defined it as a theropod animal.
However, in the 1990s a group of researchers composed of Peer Arlberg, Jennifer Clack, and Michael Coates carried out a new reconstruction of the Ichthyostegidae, in which they represented, among other details, the hind limbs of this animal with a smaller size compared to the initial scheme presented by Jarvik.
According to these researchers, these hind legs would serve more as swimming fins; other changes made in the new representation are that they reconstruct it with 7 toes joined together by membranes. Dr. Jarvik had described him with 5 fingers.
Thanks to other later findings, this group of scientists, improved more its original reconstruction where its head was represented something smaller than in the first one and in addition it had a shorter tail.
On the other hand also the ribs and the spine were corrected, with respect to the first model. In this new model he is a little narrower and less robust than in the first one. Something that would benefit him in swimming, for example.
In fact, from this last more complete and detailed reconstruction, it is believed that this animal would find it difficult to walk on solid ground, despite having “legs”; that is why it is estimated that it would crawl on the ground pushing itself with its front extremities.
Where did the Ichthyostega live?
It is considered the missing link between fish and the first vertebrates that populated the earth.
This species lived in the upper Devonian, approximately 365-360 million years ago.
With respect to its habitat, it is attributed to live near rivers, lakes and swamps. In short, places where it could swim, both to find food and to live in relative tranquility.
However, it is believed that at certain times he was forced to go out to the mainland in search of food. This is why it evolved into other species that would be more terrestrial than aquatic.
What did the Ichthyostega eat?
This animal had long, sharp teeth, which showed it was a carnivore.
About what it ate… it is speculated that in addition to feeding on fish, it would have also eaten multiple insects and small land animals.
General characteristics of the Ichthyostega
The Ichthyostega could be about 2 meters long and about 20 centimeters high, while its weight was about 90 kilos.
As we have already mentioned, it is considered by many scientists as the missing link that connects the first amphibians with the fish.
Its skull was very similar to that of primitive fish; it was characterized by being relatively large, with small eyes located on its dorsal fins, which allowed it to have a good field of vision; and its nostrils were located on the top of its head.
Some researchers also point out that the ichthyostega had small specialized cavities that would serve as its ears.
As for its body… it was covered with small scales and had a very strong backbone compared to the fish of that time.
This feature is thought to be due to adaptation to life on earth.
His ribs were as strong as the spine in order to support the weight of his whole body while he was out of the water.
This animal had some pseudo-legs, since these were not really useful for moving around on land; it is rather “designed” for swimming as reflected by the seven fingers connected to each other by a membrane.
And to finish, we will comment that its tail was shaped like a fin and was used to propel itself inside the water, as if it were a fish.
How it behaved
This tetrapod had an aquatic rather than terrestrial lifestyle, in its aquatic environment it could feed on small fish and insects. In turn he was also easy prey for other predators like the fearsome Tiktaalik, for example.
It is suspected that he took the big step out to land life, so to speak, because the sea was full of other dangerous predators with which to compete for food; if he was not the food itself.
And since the land was practically unpopulated, it would be easier for him to find something to eat.
As for their reproduction, it is believed that it was very similar to that of amphibians today; they laid their eggs in water, where they grew to maturity and then became part of life on earth; good and aquatic.
Theory of Ichthyostega extinction
I must begin by saying that in the era in which this animal lived, the earth was inhabited only by insects and large, lush, fruit-bearing trees.
On the contrary, we find oceans and seas that were full of large fish, where some were large and ferocious predators and others were the prey.
… well and that on more than one occasion the predator also became the prey when being devoured by an animal bigger than itself. You know the saying “the big fish eats the little fish”.
According to many scientists, the Ichthyostega was the animal that took the first step towards the first vertebrates inhabiting the earth; motivated mainly to be able to feed themselves.
In this way the passage of amphibians to the earth would take place and from there the dinosaurs would arrive.
However, these animals became extinct over 400 million years ago in the so-called Devonian Mass Extinction; which consisted of two major events that devastated much of the species that inhabited the planet earth at that time, affecting mainly marine and tropical areas. The following occurred:
The first event consisted of a great fall in temperatures and it took place in the marine regions; taking into account that at that time the temperature was warm and many species were adapted to that climate, this change was devastating for many species.
In addition, sea levels dropped significantly as most of them froze over creating glaciers.
This event killed more than 82% of marine life.
The second event was due to a somewhat unusual condition, which was that there was a decrease in oxygen on land that gradually suffocated the life forms that inhabited the unstable globe of that era.
These two events were undoubtedly destructive for many species, some managed to survive and evolve to adapt to the new world, but others like the Ichthyostega became extinct like other specimens. Not before leaving a mark on the path of evolution.
Some curiosities about the Ichthyostega
There is a funny intro from “The Simpsons” that shows how evolution takes place from small cells, through the Ichthyostega, dinosaurs and finally man. You can see it here.
So far no fossil remains of their hind limbs have been found, so the limbs that we often see in the illustrations are the product of researchers’ theories of what they might have been like.