Dinosaurs existed for 165 million years.

The animals' evolutionary success was partly due to their fast growth rate.

A new study finds that this pattern of fast growth appeared in the earliest dinosaurs.

The researchers examined microscopic details in dinosaur bone fossils from Argentina.

The details showed that the earliest dinosaurs had growth rates similar to animals found today like mammals and birds.

Scientist Kristi Curry Rogers of Macalester College in Minnesota studies fossils.

She is the lead writer of the research recently released in the publication PLOS ONE.

She said, "Growing quickly allows organisms to escape the risky business of being small for a long part of their life history." And she added that it also allows them to reproduce more throughout their life.

That means each following generation will be more successful.

The researchers examined patterns fossilized within the bones of dinosaurs and some of their relatives.