To celebrate National Fossil Day USA 2020, Dr. Andrew Mathers (X-ray CT Applications Engineer) scanned two fossil shark’s teeth and a modern day shark’s tooth to reveal their internal structure.
National Fossil Day is hosted annually by the National Park Service and the American Geosciences Institute, on the Wednesday of Earth Science Week, in October. This day is used as a platform to promote public awareness and stewardship of fossils, as well as to foster a greater appreciation of their scientific and educational value.
The fossilised teeth were from a Prehistoric Giant Mako (Cosmopolitodus hastalis) from the Plio-Pleistocene era, found in Suffolk, UK, and a Megalodon (Otodus megalodon) from the Mio-Pliocene era, found in Georgia, USA. The modern day tooth was from a Great White (Carcharodon carcharias), found in Western Cape, South Africa.
Prehistoric Giant Mako’s fossilised tooth
Megalodon’s fossilised tooth
Despite the age of the fossilised teeth, the degree of preservation is high enough that fine internal details, including some of the nerve and blood vessel channels, can still be visualised non-destructively, using X-ray CT. For comparison, the modern day Great White tooth shows these channel structures in abundance.
Each individual X-ray CT scan of the shark’s teeth was acquired at a matched power (Watts) and voxel resolution (µm), of 23, 33 and 24, for the Prehistoric Giant Mako, Megalodon and modern day Great White, respectively. All scans were acquired using a Nikon XT H 225 ST, which houses a Nikon 225 kV microfocus X-ray source fitted with a tungsten reflection target, coupled with a Varex 4343-CT flat panel detector. Due to the high aspect ratio of the teeth, each scan was performed using X.Tend (Nikon’s advanced approach to helical CT) to provide greater voxel resolution than conventional circular CT. For these scans the detector acquired between 4600 and 5800 projections at an exposure time of 500 ms and a gain of 36 dB.
Great White Shark’s modern day tooth
X-ray CT data sets were reconstructed in Nikon CT Pro 3D, using Nikon’s advanced helical CT reconstruction algorithm, which provides industry leading speed without compromising quality. The resultant 3D data was rendered using the isosurface renderer in Volume Graphics Studio Max 3.4.