Mini Dino torpedoes bird evolution

Trend for small size apparently evolved independently of other flugvorbereitenden conversion

A pack of raptors attacks a dinosaur © John Sibbick
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Small, fast-running dinosaurs are considered ancestors of all birds today. But before the "jump" into the air some adjustments were necessary. In what order these happened, one believed to know - until now. For a found in Mongolia mini Dino throws some of the common theories over the pile, as researchers in "Science" report.

All of today's birds go back to a group of dinosaurs, also known as "paraves". Among them, only one subgroup ultimately led to the development of the birds, but two others did not. For a long time researchers were of the opinion that certain characteristics such as the small body size, only in the later leading to the birds subgroup trained, but not in the other two. The new study, led by Julia Clarke, Assistant Professor of Paleontology at North Carolina State University, now shows for the first time that this is not the case. At the same time, it refutes the assumption that the gradual reduction in size - the prerequisite for flying - has always been directly linked to other adaptations to airworthiness.

Too early too small

The interesting thing about the now-discovered primeval dinosaur skeleton of the species Mahakala omnogovae is its small size: it measures just 70 centimeters - according to Dino standards a real tiny. And that, although it is not one of the most advanced bird ancestors, but rather at the base of the Dromaeosauridae, the Paraves stands. This group also includes much larger dinosaurs, such as the Velociraptor, best known as nimble predator from the movie Jurassic Park. For the paleontologist, this is a clear indication that not only the immediate ancestors of the birds have "invented" being small, but possibly also the common ancestors of all three parave subgroups.

"This fossil shows that the dinosaurs of small body sizes developed many earlier than we previously believed, " explains Clarke. "And even more exciting is the fact that the animals did not stay small in a series of bird relatives' lineages, but some of them became much larger." In the late Cretaceous, there were various development trends that paralleled both size growth as well led to a miniaturization.

Miniaturization and metabolic adjustments independently

And one more thing was interesting: For if the trend toward miniaturization already existed in the upper group, not only in the immediate "pre-birds", then he must have probably also developed independently of the "preparation" for flying. And that exactly contradicts the previous ideas of paleontologists. "We've seen smaller sizes in dinosaurs and birds always closely linked to changes in metabolism and growth: they got smaller and smaller, grew faster, and finally flew, " says Clarke. "Now we notice that the trend towards a small body size is well ahead of the other changes in movement and growth strategies. This forces us to question our earlier assumptions about the causes of evolution to the bird

(North Carolina State University, 07.09.2007 - NPO)