It is the first time intact bone marrow has ever been discovered in the fossil record, according to Maria McNamara, a palaeobiologist at the UCD School of Geological Sciences, and leader of the study group that made this startling discovery. What makes it even more remarkable is the quality of preservation of the marrow.
Usually only hard tissue, such as bone, survives this length of time. However, fossils of seven frogs and one salamander (out of a total of over 120 fossils examined by the scientists) have yielded soft tissue marrow. The marrow may yet prove to contain DNA from 10-million-year-old species. The finding was made in the Teruel province of north-eastern Spain. Several deep lakes once existed in the region, which has led to many ancient species of frog and salamander being uncovered there.
The research team, which included scientists from the UK, USA and Spain, was examining fossils in the Museu Nacional de Ciencias Naturales in Madrid, when they came across what they suspected was marrow tissue in the bones of a 10-million-year-old frog fossil. According to McNamara, they did not believe that they could have stumbled upon a discovery of such major importance. The fossils had been held in the museum for over 50 years and previous examination had not uncovered the bone marrow - although the international team's study was extremely thorough, and was aided by the use of a binocular microscope.
Fossilised frog from the Teruel province of north-eastern Spain
“We saw a bit of red inside the bone but thought that it would be too good to be true for it to be bone marrow,” she said. “We brought it back to Ireland for analysis and we really couldn't believe it when we found out that it was.” Marrow is the tissue that fills the centre of large bones. There are two types of bone marrow: haematopoietic (where blood cells are produced) and fatty (consisting mostly of fat cells). The bone marrow discovered in the frog and salamander fossils retained the original texture and red and yellow colours of both types of marrow. Although preserved red blood cells were discovered in the fossilised remains of the leg bone of a Tyrannosaurus Rex, this is the first time fully preserved marrow has been uncovered. The fossils on which the marrow was discovered were found in a fossil-rich deposit dating back to the Miocene Epoch, the period of time that extends from about 5.3 to 23 million years ago. The frog and salamander fossils in this case were found to be 10 million years old.
McNamara says that the bone marrow was preserved because the bones acted as a protective shell, preventing microbes from invading the soft tissue. According to McNamara, the discovery will allow researchers to build up unprecedented profiles of how extinct species lived. If scientists could find bone marrow from dinosaurs, it could help resolve the debate about whether the creatures were warm-blooded or not, she said. The species of frog from which the marrow was extracted is now extinct, although the families to which it belonged still roam the earth. But already, fascinating differences between the modern species and their ancestors have been uncovered. For example, the researchers found red bone marrow in the salamander, which shows that its blood cells were produced in the marrow. That is not the case with modern salamanders, which produce blood cells in the spleen.
L-R, clockise: Fossilised salamander from the Teruel province of north-eastern Spain, bone marrow as viewed through a microscope, and layers of sediment as deposited in the region where several lakes once existed
Although preliminary testing was carried out on the fossils in Spain, researchers hope that further testing may uncover protein or DNA, which will enable scientists to draw up an unprecedented profile of the extinct species. In order to do this testing, the fossils on which the marrow was discovered have been transported to top-class facilities in the University of Bristol for further testing. Researchers will study the material for traces of organic molecules, such as protein and DNA. The timeframe of the study is not yet known, although researchers hope to discover information quickly. McNamara and her co-authors, Dr Patrick Orr (UCD School of Geological Sciences), Dr Stuart Kearns (Department of Earth Sciences, University of Bristol), Dr Luis Alcalá (Fundación Conjunto Paleontológico de Teruel-Dinópolis, Teruel), Dr Pere Anadón (Institut de la Ciencies 'Jaume Almera', Barcelona) and Dr Enrique (Quique) Peñalver-Mollà (Division of Invertebrate Zoology, American Museum of Natural History, New York), will all remain involved in the project, which was made possible by funding from Enterprise Ireland and supported by a higher education grant awarded by South Tipperary County Council.
Panoramic view of the Teruel province of north-eastern Spain. Several deep lakes once existed in the region, which has led to many ancient species of frog and salamander being uncovered there.
“What we intend on doing now is analysing the composition of the marrow,” says McNamara. “The structure of the marrow has been very well preserved, but it is not yet clear whether that means that the biomolecules inside will be preserved. Because the marrow was so well preserved, we are hopeful that the biomolecules will be too, which will enable us to learn more.” McNamara says that testing on fossilised bone is difficult because researchers must get to the centre of the bone before they can test for marrow. Marrow may exist in already-exhumed fossils but may have been missed because detection required breaking the bones apart.
Maria McNamara
We were lucky in that the bones were fractured already, and this allowed us to examine them,” she says. “We will use x-ray equipment if we want to examine any more specimens.” The red blood cells discovered in the Tyrannosaurus Rex were found after researchers were forced to break off of the bone in order to fit it into a helicopter. After breaking the bone, the scientists noticed the cells.
News of the discovery of bone marrow in the 10-million-year-old Spanish fossils has caused headlines around the world. As well as being featured in several prominent science journals, the discovery led by University College Dublin has been featured by BBC, RTÉ and New Scientist. If further research on the marrow proves successful as it is hoped, interest in the fascinating tale of the 10-million-year-old Spanish frog will only grow.