Two hundred million years before whales, ichthyosaurs already had grouping behavior to give birth to their young.
Births for ichthyosaurs? An international team of paleontologists recently published in the journal Cell the results of a study on this large marine reptile. About the size of a bus, it lived 200 million years ago. It seems that the place of death of many specimens is actually the place of birth.
Ichthyosaurs, prehistoric carnivorous reptiles
200 million years ago, in the Mesozoic era, large carnivorous reptiles, ichthyosaurs, lived in the seas and oceans of the Earth. These animals appeared 250 million years ago to disappear 90 million years ago. A very long reign of 160 million years. It eventually came to an end after the increasingly powerful dominance of other species such as mosasaurs and plesiosaurs.
Ichthyosaurs are vertebrates. Depending on the species, they could reach sizes ranging from 1 to 20 meters in length. These sea animals were similar to our present dolphins. Thus, they had a hydrodynamic body and powerful fins that allowed them to move very quickly through the water. Some of them could reach a speed of 40 km/h.
These carnivorous reptiles had a very long snout with strong jaws with sharp teeth. They feed on fish, ammonites (cephalopod molluscs with spiral shells) and also belemnites (cephalopod molluscs related to squid).
Ichthyosaurs were able to dive very deep and jump out of the water. They were alive like some modern lizards and even some fish. In this mode of reproduction, the embryo develops in the body of the mother, who gives birth to live offspring.
Giant animals of the modern oceans, such as the blue whale and the humpback whale, make mass migrations. They gather at the same place every year to give birth to their young. According to this study conducted by an international team of scientists, ichthyosaurs already made similar migrations to give birth to their offspring.
Also read: The kingdom of ichthyosaurs: each species has its own specialty
The birthplace turned into a cemetery!
Paleontologists are interested in the fossils found in the fossil deposit located in the Humboldt-Toiyabe National Forest. It is a national forest located in Nevada, USA. Fossils of ichthyosaurs belonging to Shonisaurus species were discovered in 1928. They’ve been together since it was called Berlin-Ichthyosaurus State Park. Since then, other examples have been discovered there. They have since been protected from the climatic elements by a special structure reminiscent of a barn.
Excavations were carried out there in the 1960s. They uncovered the remains of about 37 ichthyosaurs. For more than 50 years, paleontologists have been trying to understand why so many fossils of these prehistoric reptiles were found in one place. Some scientists think that the reason for the death of these reptiles could be mass congestion, as is the case with some populations of marine mammals today. For others, toxic algae could multiply and cause death. So far, no scientific evidence has come forward to support any of these hypotheses.
Researchers have tried to explain this prehistoric mystery. For this, they used many techniques such as 3D scanning and geochemistry. They also reviewed an incredible amount of archival documents, field notes, photographs and maps of the site. They looked through the collections of museums in the region to find fragments to reanalyze.
Also Read: Did Plesiosaurs Fly Underwater?
Small remains of embryos and newborn ichthyosaurs
Paleontologists took rock samples. They then conducted geochemical tests to see if there was any disturbance in the environment. They analyzed carbon levels and looked for evidence of an increase in marine sediments causing severe oxygen depletion.
Finally, the researchers found no indication that ichthyosaurs would have died out after the cataclysm that disrupted the ecosystem. The study also suggests that after their deaths, the bones sank to the bottom of the sea instead of being trapped, which rules out the hypothesis of mass curling. So the mystery remains intact!
The researchers found something else. While working on fossils hidden in the collections of various museums, they discovered small remains of ichthyosaurs. Using a micro-CT X-ray scanner, they realized they were dealing with embryos and hatchlings of a species of ichthyosaur called Shonisaurus.
Paleontologists did not find the remains of fish or other reptiles, so they also found that this was not a feeding place for these animals.
It turns out that this must be the place where these marine reptiles give birth to their young. Analysis of different layers showed that they have been there for hundreds of thousands of years.
Therefore, ichthyosaurs moved to certain places in the ocean to give birth to their young. Large marine mammals such as whales still do so today. This is evidence that this behavior is at least 200 million years old.
Also read: Ichthyosaurus, the first giant animal that lived on Earth