Probable species: Mosasaurus beaugei (based on tooth shape)

This is a really good example of a fossil looking too good to be true.  I picked this specimen up in Tintagel, England in a rock shop.  The proprietor told be that all of the teeth were real, but she wasn’t sure about the “jawline.”  Still, it was a neat piece, so I purchased it anyway.

 
On further research, I found that this is fairly typical of many of the composite fossils coming out of Morocco.  Unfortunately, they are often advertised as being genuine jaws.  Most of the genuine fossil jaws I have seen do not look nearly this pretty when they come out of the ground, and are usually fragmented and crushed.  The teeth are indeed real (mosasaur teeth are very common fossils in Morocco), and may be from the same species.  

In many cases, the “jawline” is sculpted out of glue, sand, and sometimes even modern animal bone.  My guess with this piece is that the jawline is primarily sand and glue, and possibly some plaster.  A way for me to test this would be to try to dissolve the glue in water, which would destroy the artwork. I am now also seeing “plesiosaur jaws” occasionally on the market. On the whole, they look similar to the specimen below, only with elasmosaur teeth. Since they are from the same area as the below specimen, the teeth are probably from Zarafasaura.  

If I had any further doubts that this was a composite, they were proven when one of my students accidentally dropped the specimen on one of my lab benches.  Now, on the lower right corner of the jawline, the white composite making material is exposed.  You can somewhat see the chip on the lower right corner.  The underlying composite is white in color, and looks like a different consistency than the surrounding rock.  I have seen (and helped identify) a similar, single specimen that was sold as a “cave bear claw.”  It was not a claw, and not even from a cave bear.  It was, in reality, a very nice mosasaur tooth with a sculpted root made to look like a claw.  I suspect it may have come from the same area as my composite, as the stone matrix looked very similar to what you see above.  The “root” part of the sculpture also looked very similar to the sculpted jaw material.  

If there is any lesson to take away from this piece, it is to educate yourself on what you are buying.  If something looks too good to be true, it probably is.  There is, sadly, quite a large market of fossil fakes, and many purchase them not knowing what they really are.  Some of these forgeries are very sophisticated.  If you are in the market to collect fossils, make sure only to work with reputable dealers, ideally those who have the knowledge to authenticate any fossils they pick up.