The fossil-poor period between 365 and 359 million years ago is known as the "romer hiatus" and originally spanned as much as 30 million years, british researchers write in the "proceedings" of the u.S. Academy of science (PNAS).
According to the report, the fossils now dated offer important information about the evolution of the first terrestrial vertebrates. And they showed that the gap was due to a lack of finds – and not to a lack of animals at that time.
The team of jennifer clack from the university of south hampton reports on animal remains found at several sites in the south of scotland, representing both marine and terrestrial life. With them the gap between mainly aquatic tetrapods of the devonian with many primitive features and later, terrestrial tetrapods with features of modern quadrupedal animals can be filled.
The original forms are often about one to two meters long, have fin-like limbs and long, flattened heads. The more developed animals, on the other hand, have a coarser variety and narrower heads. According to clack’s team, the fossils provide clues as to how the adaptations to life on land took place. And they show, according to the researchers, that some tetrapod lineages may have evolved much earlier than previously thought.
According to one theory, a mass extinction 360 million years ago created the conditions for modern fish and the first land vertebrates to evolve and become established. The devonian period, which began 416 million years ago and ended 359 million years ago, is known as the age of the fishes. At that time, preforms of the later land vertebrates began to adapt to life above water. 360 million years ago, at the transition from the devonian to the carboniferous, there was a turning point: many animal forms were displaced, the modern vertebrates conquered the earth. Suspected cause of the massive changes: a worldwide mass extinction, the possible cause of which is still unclear.