HISTOLOGY
In a nutshell, bone histology is a sampling method that allows scientists to study the internal structures of a specimen. Histology has been around for as long as scientists have been using microscopes to look at thin sections of microscopic structures, ranging from tiny microbes to plant cells to cancerous tumors, but it's a more recent development in paleontology. Although this is typically regarded as a destructive process because one has to cut up a nice, possibly rare fossil, it can also be thought of as "data enhancement," as Dr. David Evans from the Royal Ontario Museum (and former student of this lab) likes to call it. Although it might seem strange to partially (or completely) destroy a perfectly good fossil, histology allows us to gain additional data and insights that cannot be acquired through examination of the external morphology alone. For example, many animals will slow down during the colder seasons, leading to a deposition of a prominent bone layer often called a LAG (line of arrested growth) that is similar to a tree ring in both its periodicity (though not necessarily equal to one year) and its utility for relative aging of the animal. This, as well as other features of the bone, can also tell us things such as what kind of mechanical stresses were being exerted on the bone (related to locomotion and to environment), the general metabolic rate of the animal, and even whether the animal was pregnant in some birds and theropod dinosaurs. Histology can also be used to study more abnormal processes, such as disease or injury.
Histological preparation of fossils isn't all that different from other fields in that the sample is cut, glued to a slide, and thinned down. Because fossils are so rare, portions of the element, or even the entire element in the case of smaller specimens, will be molded and casted for conservation purposes prior to sampling. That way, if the element needs to go back on display or another researcher needs to measure it for their own research, the original information is not lost. Often we try to use incomplete specimens that wouldn't be informative for things like measurements or museum displays. After this is complete, the specimen is embedded in a clear resin to stabilize it, cut to expose the viewing plane of interest, and glued to a thin section. The section is then polished down to a height of less than a millimeter so that light can readily pass through and illuminate the structures. Because fossils are really rocks that have mineralized in the shape of the original bone, they can be studied with similar microscopes to those that geologists use. An excellent introductory resource to the history, methods, and interpretation of histology is Bone Histology of Fossil Tetrapods, edited by Kevin Padian (University of California Museum of Paleontology) and Ellen-Thérèse Lamm (Museum of the Rockies). Also see former Ph.D. student Aaron LeBlanc's step-wise explanation of the preparation process (with photos!). All of our histology preparation is done at the lab at the Royal Ontario Museum (ROM) in Toronto.
Histological preparation of fossils isn't all that different from other fields in that the sample is cut, glued to a slide, and thinned down. Because fossils are so rare, portions of the element, or even the entire element in the case of smaller specimens, will be molded and casted for conservation purposes prior to sampling. That way, if the element needs to go back on display or another researcher needs to measure it for their own research, the original information is not lost. Often we try to use incomplete specimens that wouldn't be informative for things like measurements or museum displays. After this is complete, the specimen is embedded in a clear resin to stabilize it, cut to expose the viewing plane of interest, and glued to a thin section. The section is then polished down to a height of less than a millimeter so that light can readily pass through and illuminate the structures. Because fossils are really rocks that have mineralized in the shape of the original bone, they can be studied with similar microscopes to those that geologists use. An excellent introductory resource to the history, methods, and interpretation of histology is Bone Histology of Fossil Tetrapods, edited by Kevin Padian (University of California Museum of Paleontology) and Ellen-Thérèse Lamm (Museum of the Rockies). Also see former Ph.D. student Aaron LeBlanc's step-wise explanation of the preparation process (with photos!). All of our histology preparation is done at the lab at the Royal Ontario Museum (ROM) in Toronto.
NEUTRON COMPUTED TOMOGRAPHY (nCT)
Neutron tomography is a non-invasive method of analysis similar to x-ray computed tomography (CT), differing mainly in the use of a neutron beam rather than x-rays to produce the three-dimensional image. The two are used for a lot of the same applications, but depending on the material being analyzed, one method is often preferable. In normal CT analysis, the x-rays interact with the negatively charged electrons in an atom; the more electrons, the more interaction and accordingly, higher contrast of the image. This makes this method better for detecting heavier compounds in a light matrix but is complicated by the presence of metallic minerals (like iron oxides), which lower the contrast of the image. Conversely, neutrons are neutral, so they interact with the nucleus of the atom and are particularly sensitive to light elements. In particular, NT is a useful method for materials with an abundant metallic matrix, which produces lots of background noise in x-ray CT analyses. It is also useful for materials that are highly enriched in organic (often light) elements. Although x-ray CT analyses are far more common in paleontology because of increasing availability of these instruments (i.e. hospitals), the Richards Spur material, which contains a lot of pyrite (an iron sulfide also known as fool's gold) and which is enriched in oil (hydrocarbons), makes for an excellent case study into the utility of neutron tomography. The main downside is that when certain elements are found in a sample, they can capture some of the neutrons from the beam, turning them into unstable radioactive isotopes that can take several weeks to decay before the specimen can be transported. There are only a handful of institutions in the world with the equipment to perform NT analyses; we collaborate with Dr. Joseph Bevitt at the Australian Nuclear and Science Technology Organisation (ANSTO).
A good general overview of neutron tomography can be found on the website of the Paul Scherrer Institute, one of the first institutions to develop the infrastructure for the method.
A good general overview of neutron tomography can be found on the website of the Paul Scherrer Institute, one of the first institutions to develop the infrastructure for the method.
- Schwarz, D., Vontobel, P., Lehmann, E.H., Meyer, C.A. and Bongartz, G., 2005. Neutron tomography of internal structures of vertebrate remains: a comparison with X-ray computed tomography. Palaeontologia Electronia 8(2): 30A. [PDF]
- Sutton, M.D., 2008. Tomographic techniques for the study of exceptionally preserved fossils. Proceedings of the Royal Society of London B: Biological Sciences 275(1643): 1587-1593. DOI: 10.1098/rspb.2008.0263