FIB-SEM of Ancient Bones Reveals the Origin of Mineral Metabolism
Paleontologists use a novel approach with focused ion beam scanning electron microscope (FIB-SEM) on fossils to provide evidence for early osteocytic bone evolution.
Bones provide the scaffold for all movements of vertebrate animals. Bone has been studied extensively; however, little is understood about its evolutionary origin. While our bones have osteocytes, which are cells embedded in our bones, not all species’ bones do. This leads paleontologists to wonder why early bony vertebrates developed osteocytic bone.
A scientific article from Dr. Florian Witzmann’s lab at the Museum für Naturkunde, Germany, used a novel microscope approach with focused ion beam scanning electron microscopy (FIB-SEM) to provide evidence for early osteocytic bone evolution.
The Witzmann's lab overarching goals are to understand deep time development. We use fossils as well as modern animals to bridge the gaps in our understanding of evolutionary changes in physiology. I study the evolution of bones. I mainly focus on fossils, which means the organic components are long gone. I use cell spaces that are left behind to understand cell structure.
A Research Roadblock
Bone cells live inside caves created by the bone mineral, called lacunae. Ms. Haridy was hoping to image and understand early osteocyte lacunae and overall early bone evolution in ancient fish, which lived approximately 420 million years ago.
However, the imaging technologies commonly used in the paleontological world – transmitted light microscopy, 2D transmission and scanning electron microscopy and micro CT – did not provide the necessary, high resolution 3D visualization I required. She was frustrated that this project would not progress and was considering abandoning this line of research.
Applying a Tool for Battery Research to Bone Fossils
Focused Ion Beam Scanning Electron Microscopy
Ms. Haridy was working with collaborators in Dr. Ingo Manke’s group at the Helmholtz Zentrum Berlin (HZB). This group works in a completely unrelated research field – energy materials, fuel cells and batteries – but they also run the imaging facility and have been consulting with Dr. Witzmann for some time on micro CT scanning of fossils. When walking down the hall at the HZB, she saw some amazing, high resolution, 3D images that looked topographically very similar to osteocyte caves. It turns out they were actually images of fuel cells and the technology used was FIB-SEM. This inspired her to try this technology on fossils – before which had never been done.
Osteocyte from Fossils of Ancient Fish Bone
Imaged using ZEISS Crossbeam FIB-SEM
Evidence of Mineral Metabolism
As published in Y. Haridy et al., the team found evidence of mineral metabolism in the earliest cellular bone tissues. One of the things that osteocytes can do is eat the bone around them and redistribute that mineral back into the bloodstream – a process called mineral metabolism. The skeleton is a mineral storage unit and, if organs are starving for certain minerals, it can be broken down to share those minerals. Using FIB-SEM, Ms. Haridy and team were able to find evidence of mineral metabolism in ancient fish. It is very likely this evolutionary advantage that bones with osteocytes became the prevailing model for millions of years after that.
We hope to apply FIB-SEM to other early fossil material to look at early tooth making cells as well as to continue understanding ancient bone and cartilage better, and even want look at fossil feather structure. The only limit is the preservation of the fossil and the field of view, so we are looking at small specimens that can answer big questions.