A histological study of a femur of Plagiosuchus, a Middle Triassic temnospondyl amphibian from southern Germany, using thin sections and micro-CT scanning

Abstract

AbstractThe histology of a femur of Plagiosuchus, a Middle Triassic temnospondyl amphibian, is described on the basis of two supplementary methods: classic thin sectioning and micro-CT scanning. In addition, the effectiveness of high-resolution micro-CT scanning for histological analysis is assessed. A classic, mid-shaft thin section of the femur was prepared, but prior to slicing two micro-CT scans were made. One of these has an image stack of a total of 1,024 images in the horizontal plane and a slice thickness of 87.8 μm, so that the entire bone could be captured, while the second was at mid-shaft region only, yet with a higher resolution of 28.3 μm and an image stack of 787 images in the horizontal plane. The classic thin section shows a very small medullary region which is surrounded by a layer of endosteal bone. The thick cortex is highly porous with numerous large, mainly longitudinal, vascular canals arranged in layers. In the deepest cortex woven bone occurs and primary osteons had locally started to form (incipient fibro-lamellar bone), which gradually passes into parallel-fibred bone and more lamellar bone close to the outer surface. Remains of a Kastschenko line were identified, enabling a reconstruction of the entire growth record. Five Lines of Arrested Growth (LAG) could be counted. The micro-CT scan enabled observations of the ontogenetic growth stages and calculation of growth rate on the basis of a single specimen. The micro-CT scan permitted a reconstruction of the ontogenetic development and the exact deposition rate per annum. Moreover, at higher resolution the micro-CT scan revealed data on micro-anatomical characters, such as porosity and skeletochronology (growth mark count). In conclusion, micro-CT scans do provide an alternative in cases where thin sectioning of the original bone is not possible.