Heavy metal manatees

Researchers from the University of Manchester (UK), Diamond Lightsource (UK) and College of Charleston (USA) have utilised some of the brightest light in the universe to reveal for the first time the chemistry of bone growth in living and 19 million year old sea cows.

Over millions of years, sea cows (Sirenia) have evolved unusually dense bones, which helps counteract their buoyancy in water. This permits them to counter buoyancy and stay close to the sea floor and the plants on which they graze without having to expend energy while remaining submerged. The manatees and dugongs are thought to have been mistaken for mythical mermaids (sirens) by sailors. Some extinct species, Hydrodamalis gigas, weighed up 8 tons and were 10 metres long. Sea cow bones are much denser than most other animals, a function of their unique bones growth. Most animals ‘hollow out’ the centre of their skeleton and deposit new bone material around the bones circumference, which makes the whole organism lighter. Sea cow bones are solid and dense with new bone being deposited all the way through some skeletal elements. It is like building scaffolding with solid rods of steel, as opposed to the normal light hollow poles that make scaffolding possible. The much denser bone could only be supported by an animal with an aquatic lifestyle, given a land animal would find such skeletal mass a major obstacle for location. For those interested in imaging bone growth, sea cows offer spatially large bone samples that are perfect for study.

Dr. Jennifer Anné, the lead author of the study said “Bone remodelling is the continuous process where bone is being ‘eaten’ and then ‘laid down’. This process is essential for maintaining bone strength and is carefully controlled by processes utilising trace elements such as zinc. As such the distribution of these trace elements within microscopic bone structures can indicate bone remodelling stages, and thus being able to see these trace metal distribution could help us understand bone health implications both in humans and extinct organisms.”

By using X-rays generated by the Diamond Lightsource (UK) synchrotron particle accelerators, the research team were able to produce detailed images of where the various elements of the periodic table were located within both living and fossil sea cow bones. The chemical maps were also able to show how these elements were combined within the bone chemistry for the very first time. The work clearly shows that the distributions of calcium and zinc in the 19 million year old fossil bones were almost identical to modern bones.

We found that in the modern bone, each element was concentrated in distinct structures called secondary osteons and connecting canals, revealing both physiological processes and histological features not seen before. So we weren’t just imaging the microscopic shape of the bone but actual biological processes that were occurring up to the time of death.” says Dr. Jennifer Anné.

Co-author Professor Roy Wogelius, from Manchester’s School of Earth Atmospheric and Environmental Sciences said: “One of the most astonishing finds was the similarity between the modern and fossil samples. We were going through our scans and we thought we had scanned the same sample twice! They are that similar both structurally and chemically despite being separated by 19 million years.”

This research is not the only time the team has uncovered such beautiful preservation of chemistry within the fossil record. They have previously found similar levels of preservation, in birds, dinosaurs, reptiles and plants up to 150 million years old.

Co-author Professor Phil Manning from the College of Charleston (USA) and University of Manchester (UK) said: “The UK’s Diamond Lightsource and other synchrotron facilities around the world offer a technologically-driven paradigm shift in our understanding of life on Earth, both present and past. We are in the midst of an interdisciplinary renaissance that is gaining new insight from shedding the brightest light in the universe upon fossil remains. Such studies are only possible through the successful collaboration between multiple disciplines and the tremendous support of an outstanding synchrotron facility.”

Details of this research appear in the journal Metallomics and come at a perfect time, shortly after Manatee Appreciation Day.

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