Considering that it is at least 220 million years old, the quality of this tooth amazes me. It is from a North African Rutiodon (they are also found in N.America) - a late Triassic phytosaur.
I find in almost impossible to get my mind around this sort of time scale - when you think, that the Rutiodon was a lot further back in Tyrannosaurus rex's past than T. rex (at 65-85 million) is in ours.
Although not closely related (and much more heavily armoured), they were very crocodilian in appearance, only with their nostrils located up close to their eyes. Estimates of size vary a bit, but are generally in the order of 12 to 15 foot. For more info and an illustration of the animal see this website:
http://www.paleodirect.com/phyto1.htm
I have no idea what the white marks are, they maybe spoil the overall "look" a bit, but on the plus side they helped make this tooth affordable.
The tooth enamel is quite reflective and I had some problems with lighting. Microscope was a Meiji EMZ-5TR with Olympus SP-350 and Brunel adapter. All images stacked (pic1=10, pic2=12 and pic3=8 ) with CombineZ5.
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