A controversial study claims that the world’s first known insectivorous mammal lived alongside the first dinosaurs some 225 million years ago. Recent research puts the emergence of mammals back about 20 million years.
Quoted from Live Science, the international team of researchers examined the fossil remains of a 20 cm long animal named “Brasilodon quadrangularis” and concluded that this animal was a mammal. The key feature of this ancient animal is having two sets of teeth similar to most mammals, including humans, throughout life. The researchers of a recent study now claim that Brasilodon is now the oldest mammal known to science. Therefore, according to this fossil record, Brasilodon lived about 20 million years before the previously known oldest mammal, the sauropod.
However, the classification of early mammals is a highly complex issue. In this regard, a researcher who was not involved in this research told Live Science that neither Brasilodon nor the mergandans are mammals, and both have a position behind mammals in the evolutionary tree despite having teeth similar to mammals.
The classification of the first groups of mammals is one of the hot debates in the world of paleontology.
Considering that the researchers were unable to find mammary glands among the fossils, they looked for other evidence of the ancestors of mammals in their mineralized bones and teeth. As you know, one of the prominent features of mammals is two sets of teeth, milk and permanent teeth, which develop at different stages of life. In contrast, reptiles and fish (those with teeth) often shed their teeth several times during their lifetime.
The researchers examined three Brasilodon lower jaws (one belonging to an immature specimen and two adult jaws) that were discovered a few decades ago at the Linia Sao Luis archaeological site in southern Brazil. They then checked the growth of the teeth by cutting them. Since the researchers had many fossils of Brasilodon at their disposal, they decided to use these destructive techniques.
According to the researchers, Brasilodon was very similar to today’s mammals despite having two sets of teeth
Martha RichterOne of the researchers of this study from the Natural History Museum in London stated in this regard: “From the studies, we learned that Brasilodon’s teeth were changed only once during its life.” The presence of two sets of teeth makes Brasilodon a difiodont, that is, an animal that had two sets of teeth during its lifetime. This fact suggests that Brasilodon had more mammalian features than reptiles.
Richter continued: “But we don’t have any examples of reptiles that have only two sets of teeth. “Old reptiles were constantly changing their teeth.” Research suggests that difiodont teeth are the result of a genetic chain of events that not only changed the shape of the skull and teeth, but also affected other bodily functions in mammals. Endothermy (the ability to regulate body heat), milking and fur removal are among the features that are more known in mammals, and more importantly, these features are all related to each other.
Brasilodon [تصویر شاخص مقاله] It was an animal similar to today’s mammals with a long tail and other features similar to insectivores. By placing Brasilodon in the mammal category, this animal has a special place in the evolutionary tree, a place that belongs to animals that survived two extinction events – including an asteroid impact that killed all non-avian dinosaurs 66 million years ago during the Cretaceous period. They survived. These extinction events greatly contributed to the diversity of mammals in all land and water areas of the planet. However, the results of the new findings have not managed to attract the attention of all researchers.
Proof of the researchers’ findings means that Brasilodon survived two mass extinction events.
Simon HoffmanA researcher from the New York Institute of Technology, who specializes in the history of the evolution of early mammals, said in this regard: “This research does not provide any information that would change the position of Brasilodon.” [در درخت تکاملی] help. “According to other research, Brasilodon is not a mammal, certainly not the oldest mammal, and not even a mammal.”
Hoffman notes that researchers in recent research have used “mammals” and “mammalians” almost interchangeably. He goes on to explain that this is common in the scientific community, however, it is clear that these groups should be considered separately. “Mammalians are a group that is further down the evolutionary tree than mammals,” says Hoffman. Actually, [در سوابق دیرینهشناسی] “Mammals are those fossils that later evolved into mammals.”
According to Hoffmann, the meerkats are the first known mammals, while he believes that Brasilodon usually belongs either as a sister group to mammals or as a sister group to another larger clade, such as mammals, in the evolutionary tree.
Diffudent teeth are a well-known feature of mammals, but as exciting as the discovery of Brasilodon is, it doesn’t necessarily mean the animal can be classified as a mammal, Hoffman said. Animals regularly inherit characteristics from their ancestors, and at the same time, life is constantly changing and evolving, and new branches are added to the evolutionary tree.
“We used to think that feathers were a key feature of birds,” Hoffman continues, “but now we know that feathers evolved much earlier than we thought, and just because we recreate a T-rex with feathers doesn’t make him a bird.” Let’s call it a bird.”
Richter also admits that his and his colleagues’ research findings have caused a lot of controversy. He notes that the classification of the first mammal groups has always been controversial, and the debate over how to classify early mammals continues. In the end, Richter expressed hope that this research can help clarify this debate to a great extent.
Feature image: Artist’s reconstruction of Brasilodon quadrangularis next to dinosaurs