In Australia, researchers have examined the fossil upper arm bones of an extinct relative of the still living toilet animals. Structure and microstructure of the bone provide insights into the way of life of this egg -laying mammal, which lived at the time of the dinosaurs. According to this, Kryoryctes Cadburyi was a semi -quatic mammal that could swim well today, but dug into the ground on land caves. The find also explains the evolution of the nicrings relatives relatives, but in many ways of different antigel.
There are very few among the approximately 6,000 existing mammal species. These so -called toilet states include the edge animal (ornithorhynchus anatinus) and four ants (tachyglossidae) that live in Australia and New Guinea. The joint ancestors this curious group of Ursäugs developed is controversial among experts. So far, fossils that could clearly show the history of evolution have so far been found. Tooth comparisons with today’s mammals are also not possible because the toilet animals have no teeth. So only theories remain.
One of the hypotheses states that ants have emerged from a common, platform-like ancestors. However, this hypothesis speaks that the appearance and lifestyle of today’s toilet animals differ considerably. The spiky ants are land mammals that feed on insects and groundworms. On the other hand, platform animals live semi -quatic, i.e. both on land and in the water, where they prefer invertebrate residents of fresh water. For this they have developed a beak, a waterproof fur, swimming skins on their feet and a beaver -like tail. In addition, caves dig into the ground.
Ober arm bones reveals lifestyle
In order to learn more about the evolutionary history of the egg -laying mammals, researchers around Suzanne Hand from the University of New South Wales in Sydney have now examined a single fossil upper arm bone (humerus) of an extinct Ursäug. The species called Cadburyi lived in Australia about 108 to 103 million years ago in the early Cretaceous period and has morphological similarities with the lifting toilet animals. His bone was found around 30 years ago in the Dinosaur Cove fossil service in the south of Victoria. The team around hand has now scanned this remnant in detail, examined its microstructure and compared the characteristics with those of the platform animal, two antigel species and 82 of other living mammals.
The analyzes showed that the upper arm bone of Cryoryctes cadburyi It was around five centimeters long and probably belonged to a 2.5 to five kilogram animals. In its overall form, the bone is more like that of the ants than that of the platform, as the team reports. The greatest similarity to non-egg legends is with the seater (Enhydra Lutris). The bone of Cryoryctes cadburyi However, showed a thick wall and a small central cavity for the bone marrow – features that can be found in the striking animal, but not with ant igars. The comparisons with other mammals showed that such compact bones with a small central cavity are typical characteristics of mammals that live semiaquatic and grabic, such as nutrias, bisamrats or otters. “Your heavy bones look like ballast so that you can easily dive when looking for food,” says Hand. The high bone density reduces the buoyancy when swimming, but complicates running ashore, as the researchers explain.
Notes on joint ancestors of the toilet animals
Together, these results suggest that Kryorycytes Humerus was also a semi -quatic, graving toilet animal, similar to the platform today. The same was probably true for their common ancestors. “This indicates that the amphibious way of life of the modern platform had its origin at least 100 million years ago, during the age of the dinosaurs, and that antigel developed from semi -quatic ancestors,” said the team. According to this, the findings support the hypothesis that the country -living ants also developed from a semiaquatic ancestor that lived similar to a plat animal. Only later in the Evolution did the ants apparently return to the terrestrial lifestyle and developed a more suitable appearance, including lighter bones. Such a country gang is a “extremely rare” process in the evolutionary history of the earth, as the team emphasizes.
When exactly this happened is still unclear. Hand and your colleagues now hope for further fossil finds in order to be able to narrow down the evolution of the egg -laying mammals. “If he is found, his thigh bone could provide further indications of how much time Kryoryctes could have spent on land,” the researchers write.
Source: Suzanne Hand (University of New South Wales) et al.; Proceedings of the National Academy of Sciences (PNAS), DOI: 10.1073/PNAS.2413569122