Mammalian boom without dinosteroben
Corrected pedigree of the mammals proves independent evolutionary thrusts from the dinosterbeneRead out
So far it has been believed that the massive spread of mammals was only fueled by the extinction of their biggest competitors, the dinosaurs. However, a new study in "Nature" now holds a surprising result: the two largest developmental stages in the evolution of mammals were between 100 and 85 million as well as 40 to 35 million years ago. On the other hand, the large amount of dinosterbene was precisely between these times and thus did not trigger the "triumphant advance" of the mammals.
It was one of the biggest natural catastrophes that ever hit our planet: a mile-long meteorite crashed on the ground near the Yucatán Peninsula in the Gulf of Mexico some 65 million years ago, eroding much of its life. Not only the dinosaurs - which until then dominated the earth - but also most of the other plant and animal species fell victim to the climate change caused by the impact.
Birth of mammals?
"So far, it was assumed that the meteorite impact at the end of the Cretaceous and at the beginning of the Tertiary was the 'birth' of today's mammals, " says dr. Olaf Bininda-Emonds of the Friedrich Schiller University Jena. But the evolutionary biologist from the Institute of Special Zoology and Evolutionary Biology, together with an international research team, was able to show that this hitherto common assumption is wrong. His research results are published by the team around Bininda-Emonds in today's edition of the renowned science journal "Nature".
In it, the researchers present for the first time a nearly complete pedigree of all mammal species today. This "supertree" of mammals contains 4, 510 species - and thus 99 percent of all known species. For four years, biologists have collected all available data and put together existing single-parent trees, such as predators and primates. "The pedigree shows the different sizes of each group of mammals, explains Bininda-Emonds and points to the circular structure of the" Supertree ", which branches out ever finer from a ring in the middle outward. "The largest group of mammals are the rodents, " continues Bininda-Emonds. "They represent nearly 2, 000 species and thus almost half of all mammals." Other groups, such as the "pangolins" consist of only seven representatives. display
Branches analyzed in the pedigree
But completeness alone makes the scientific value of the pedigree of mammals, which Dr. Ing. Bininda-Emonds and his colleagues from the US, UK, Australia and Canada have not yet done so. "From a traditional pedigree, nothing can be seen at what time in the evolution of the branches - ie the individual groups and species have emerged, " says Bininda-Emonds. And it was precisely this information that the German Canadian, who is conducting a Heisenberg scholarship at the University of Jena, was able to determine for the first time for all mammals. Based on genetic information of recent species calibrated by fossils of known lineage and kinship, the scientists were able to estimate the "divergence times", ie the periods after which a branching occurs. In this way, they developed a timescale where they can now read when it came to the ramifications in the evolution of mammals.
"We wanted to find out when the ramification of the pedigree was particularly strong, so when many new lineages and species emerged, " Dr. Bininda-Emond. To the surprise of the researchers, however, that was not the time around 65 million years ago when the dinosaurs died out. "All 18 orders of today's higher mammals (placental animals) are already much older, " says the Jena evolutionary biologist. They all originated in - for evolutionary processes - shortest time: around 100 to 85 million years ago. A second major development spurt of the mammals began only about 40 to 35 million years ago. At that time, most of their current representatives. What has delayed the development of today's mammals up to this time is so far unclear. The fact that the dinosaurs disappeared from the earth, the development of the mammals certainly did not, as previously assumed, flourished .
(idw - Friedrich Schiller University Jena, 30.03.2007 - AHE)