This is a GENUINE fossil Spinosaurus dinosaur tooth. This tooth is unusual in that instead of it having a round cross-section, it was flattened over time from burial pressure. Despite its price, it is large and from a full-grown, adult Spinosaurus dinosaur.
Spinosaurus is estimated to have been THE LARGEST of all meat-eating dinosaurs that ever lived. With a length of 41 to 59 feet long, 20 feet high and weight estimates from 4 to 20+ tons, it was truly a behemoth! Spinosaurus was considered a bipedal dinosaur that is, one that walked on two feet although, its robust arms could have been used to allow the animal to walk on all fours at times. An extremely long snout was lined with an array of straight, conical teeth.
WARNING: A common trick to fake large dinosaur teeth in the market is to attach either a bunch of sand mixed with glue on the end of the tooth's root to exaggerate the length or even worse, fabricate a giant impressive tooth by combining and blending multiple teeth sections together to appear as one massive tooth or to fabricate the bottom portion of the tooth and extend, by a much as DOUBLE OR MORE, the original length of the tooth before work started. The workmanship of a few notorious United States-based fakers is of the finest workmanship and VERY convincing in appearance. There have been European fakers also known to create and sell these large teeth. Don't be fooled when you are shopping for large dinosaur teeth of ANY SPECIES, not just Spinosaurus. These are common practices of both unscrupulous and uninformed dealers. We see these "doctored" large dinosaur teeth offered quite frequently and numerous junk, worthless teeth that have been converted and heavily modified are selling for ridiculously high prices, mostly at shows and on the internet. Ebay is one of the worst places for this where fraud runs rampant and unchecked in the entire rare collectibles field but some fossil show dealers and internet sites have been pawning these "creations" off for years now, as well!