ICHTHYOSAUR: CHARACTERISTICS, EXTINCTION, FEEDING, REPRODUCTION, FOSSILS - BIOLOGY - 2025

The ichthyosaur was a type of aquatic reptile that belonged to the Sauropsida class and inhabited the Earth's oceans between the Triassic and Cretaceous periods. Its main characteristic is that they had a certain resemblance to today's dolphins.

The order Ichthyosauria was first established by the French naturalist Henri Ducrotay de Blanville in 1835. However, the first complete fossil appeared much earlier, in 1811. This was a class of reptiles that was especially diverse, consisting of seven families, all extinct to this day.

Graphic representation of various Ichthyosaurs. Source: Nobu Tamura email:

These reptiles were distributed by all the seas of the world geography. Its fossils have been found in greater quantity on the English coast, the state of Nevada and in the southern area of ​​Chile. Thanks to the large number of fossils that have been collected, it is one of the best-studied primitive reptiles.

General characteristics

Ichthyosaurs were aquatic reptiles that, from a morphological point of view, had certain similarities with today's dolphins. They were large animals, being able to measure up to approximately 18 meters. Their bodies were spindle-shaped and they had a tail similar to that of lizards.

On its head, two structures stood out widely: the muzzle and the eyes. As for the snout, it was elongated and had a pair of jaws with numerous teeth, which served to feed on various marine animals.

Ichthyosaur skull fossil. Source: David Ceballos from Madrid, Spain

The eyes were quite large. They have even been described as the largest organs of vision in the animal kingdom. These were protected by a very resistant orbital basin. Due to the great development of their eyes, this animal had the ability to see well at long distances and in the dark, which is why they used to hunt at night.

Ichthyosaurs had a fairly large dorsal fin and tail fin. In addition to this, their legs were modified as fins, but they kept the fingers. They could have between 5 and 12 fingers. It is important to note that ichthyosaurs were quite fast animals, which could reach more than 40 km / h.

These reptiles had a type of lung respiration, so they had to rise to the surface from time to time to take air. In this they also resembled dolphins.

Taxonomy

The taxonomic classification of the Ichthyosaur is as follows:

-Domain: Eukarya

-Animalia Kingdom

-Filo: Chordata

-Subphylum: Vertebrata

-Class: Sauropsida

-Subclass: Diapsida

-Order: Ichthyosauria

Extinction

Until recently, the reason for the extinction of ichthyosaurs was unknown. Specialist paleontologists had not been able to find the exact reason why they disappeared from the face of the Earth.

However, in 2017 a group of scientists managed to establish the possible reasons why this group of animals became extinct millions of years before the dinosaurs did.

In this sense, it has been established that ichthyosaurs became extinct mainly due to two causes. The first of them has to do with its reduced evolutionary rate and the second with the climate change that the planet experienced in that period of time.

Low evolutionary rate

Regarding the low evolutionary rate, it can be said that, although the ichthyosaurs were a very diverse group during their last stage of life, the truth is that they remained unchanged for a long period of time. This according to data collected by specialists of the fossils that have been collected.

The fact that ichthyosaurs did not experience any modification in thousands of years, made them unable to adapt to the possible environmental changes that could occur.

Various species of Ichthyosaurs. Source: Nobu Tamura (http://spinops.blogspot.com), compiled by Levi bernardo

It is important to remember that the foundation of evolution is mutations, small changes at the DNA level that translate into changes at the morphological level, which in turn allow living beings to survive in a changing environment.

Climate change

However, climate change was another element that seemed to play an important role in the extinction of ichthyosaurs. During this time, the temperature of the waters increased notably, as did the sea level. This as a consequence of the melting of the poles, since at that time the Earth's poles were not covered with ice.

According to observations by specialists, climate change by itself did not pose a threat to ichthyosaurs. The problem was that it resulted in a clear reduction in food sources, as well as a change in the migratory routes of this and other species and the appearance of animals that competed with ichthyosaurs for different resources.

By meeting all these conditions, it becomes clear that the environment became hostile to ichthyosaurs, which is why they ended up becoming extinct before the end of the Cretaceous period.

Reproduction

Taking into account that ichthyosaurs were vertebrates, it can be said that the type of reproduction they had was sexual, as is the case with most of these. As is well known, sexual reproduction involves the fusion of gametes, that is, a female sex cell (ovum) and a male sex cell (sperm).

As with all reptiles, fertilization in ichthyosaurs was internal, which means that the male had to deposit the sperm inside the female's body.

With regard to the type of development, specialists seem to disagree, since there are some who argue that ichthyosaurs were viviparous organisms and others claim that they were ovoviviparous. In this sense, what is true is that the embryo developed inside the mother.

This has been demonstrated thanks to the collection of fossils that were found in such good condition and that contained embryos inside.

Likewise, according to most specialists, ichthyosaurs had a direct development, that is, they did not go through any type of larval stage, but when they were born, they presented the characteristics of adult individuals of the species, only smaller.

Feeding

The ichthyosaur was a carnivorous organism, which implies that it fed on other animals. According to many scholars on the subject, this reptile was considered a predator in the seas.

So far it has been established that ichthyosaurs fed mainly on fish, as well as cephalopods. Among the latter, ichthyosaurs seemed to have a predilection for one known as the belemnite.

This reptile had teeth that also allowed them to feed on other organisms such as some mollusks.

Fossils found

The ichthyosaur is one of the dinosaurs of which the largest number of fossils have been found. In addition, it has the peculiarity that they have been located in numerous parts of the planet, which is why it is said that it was distributed in all the oceans.

First fossils

In this sense, the first complete ichthyosaur fossil that is known was found in 1811 in a region of England that today is known as the Jurassic Coast.

Much later, in 1905, an expedition was carried out in the state of Nevada, where a total of 25 fossils could be collected, some of which were complete, with their easily identifiable parts.

To this day, the best preserved and most complete fossils have been found in the German areas of Solnhofen and Holzmaden. The preservation of these specimens is so perfect that they not only preserved their skeleton, but also certain soft parts of the body such as embryos, stomach contents and even the skin.

Recent Findings

In the Patagonia area, south of the South American continent, a large number of ichthyosaur fossils have also been found. Thanks to the melting of the Tyndall glacier, a rock was discovered in which there were several fossils of this animal. This meant a great advance, since their characteristics resemble those of the ichthyosaurs found in Europe, which allows us to suppose how the oceans were interconnected millions of years ago.

In Torres del Paine National Park, in southern Chile, a total of 34 specimens have been found, complete or semi-complete. These have a length that goes from one meter to 5 meters. The first find of an ichthyosaur fossil in this place was in 1997.

Ichthyosaur fossil. Source: Manurinc

As a curious fact, in 2010 a very well preserved fossil was found in this area that contained an embryo inside. In that same expedition, an ichthyosaur fossil was also obtained that was dated to the Jurassic period, which is a great find, since the rest of the fossils of this reptile found in the area are much more recent, from the Cretaceous.

Likewise, despite the fact that in the southern hemisphere of the planet, the findings have been limited to the regions of Australia and South America, in 2017 a fossil was found in the Indian region of Kachchh (Gujarat). This fossil consists of an almost complete skeleton, with an approximate length of 5.5 meters. The dating of this fossil established that it belonged to the Jurassic period.

Similarly, some English scientists have studied a fossil found in England. This belonged to a newborn ichthyosaur. The important thing about this find is that inside they found the remains of a squid, which was their last dinner.

In this sense, this discovery provided some light regarding the feeding of these animals, since it was believed that small ichthyosaurs fed only on fish. It is now known that they could also eat squid and perhaps other marine invertebrate animals.

References

1. Ellis, R. (2003). Sea Dragons - Predators of the Prehistoric Oceans. University Press of Kansas.
2. Ichthyosaurs 101. Obtained from: nationalgeographic.es
3. Jiménez, F. and Pineda, M. (2010). The terrible lizards dinosaurs. Sciences 98. Autonomous University of Mexico
4. Mesa, A. (2006). Colombian marine saurians. Conference
5. Ruiz, J., Piñuela, L. and García, J. (2011). Marine reptiles (Ichthyopterygia, Plesiosauria, Thalattosuchia) from the Jurassic of Asturias. Conference at the XXVII Conference of the Spanish Society of Paleontology.
6. Stinnesbeck, W., Leppe, M., Frey, E. and Salazar, C. (2009). Ichthyosaurs from Torres del Paine National Park: paleobiogeographic context. Conference at the XII Chilean Geological Congress.