DUBLIN, 3 August 2006 - The first fossilised bone marrow has been found in the bones of 10-million-year-old frogs, salamanders and tadpoles by scientists working in northeastern Spain, the Irish team leader said on Tuesday.

Palaeontologist Maria McNamara said the find could yield unprecedented insights into prehistoric creatures, such as whether they hibernated or whether they were cold-blooded or warm-blooded.

McNamara, a researcher at the School of Geological Sciences of University College Dublin (UCD), said her team from Ireland, Spain and the United States found the fossils in ancient lake deposits in the Libros area of Spain.

McNamara said one of the most exciting aspects of the discovery is what the marrow will be able to tell scientists about creatures that lived during what is known as the later Miocene period.

"The original organic material is still there," according to McNamara, whose research was published in this month's Geology, the journal of the Geological Society of America.

"It is still organic in composition, whereas most traces of soft tissues you find in the fossil record, which are very rare anyway, have rotted away and just the shape of the tissue is preserved in mineral," she said.

"Tissue like bone marrow carries a lot of physiological information. They can tell you the state of the organism when it died, was it healthy, did it hibernate, where did it produce its red blood cells and whether it was warm-blooded or cold-blooded," she said.

"They would be pretty important to find for some other fossil groups like dinosaurs. It could help to resolve some debate about whether they were warm-blooded or cold-blooded," McNamara said.

She said researchers were now doing tests in UCD to see if any bio-molecules, like amino acids and proteins, are preserved.

The research is being undertaken in collaboration with scientists at the Institut Jaume Almera and the Fundacion Conjunto Palaeontologico de Teruel in Spain, and the American Museum of Natural History in New York.

McNamara, who is undertaking the research as part of work for a doctoral degree, said there were a number of reasons why fossilised bone marrow has never been found before.

"Because bone marrow rots away so quickly when people die, people never thought that it could be preserved.

"Also, because you have to fracture the bones before you can see inside, obviously if you have nice fossil specimens in a museum you are not going to get permission to break them up."

The researchers were able to access the marrow from the fossils because they were found in rock that had split and some of the bones had fractured as a result.

McNamara said the original red and yellow colours of the marrow had been preserved.

"The fatty bone marrow is yellow and is a sort of energy reserve in terms of starvation or something and you also have red bone marrow and that is where your blood cells are produced.

"In the fossil bone marrow the original structure is preserved showing where the red and yellow marrow would have been but also the original colour is preserved and there are some cells preserved as well."

The main finds of marrow have been made in fossilised frogs and salamanders.

"We did find some very small fragments of bone marrow in one tadpole," she added.