Wikipedia:Reference desk/Archives/Science/2014 March 28

= March 28 =

Shark tooth to ID
My daughter found what looks like a shark tooth in her school yard (I'm assuming the previous owner was a grade school kid and not a land-based mako). I've uploaded a few pictures here. Would anyone care to identify what species it's from? I think it's genuine, but if you have reason to doubt that, feel free to say so. Matt Deres (talk) 01:11, 28 March 2014 (UTC)


 * I'm no expert, but judging from the size it could be from a great white Hot Stop talk-contribs 01:30, 28 March 2014 (UTC)


 * I suspect it was a land shark, delivering a Candygram, that lost the tooth during an attack. :-) StuRat (talk) 03:51, 28 March 2014 (UTC)


 * A basic web search turns up - I don't know about this and I'm not enthusiastic about diving into the details there right now, but it seems to offer a way to figure something out.  Can the OP or someone else interested try to work through the characteristics and figure out which ones can be deduced from this picture, and if more pictures are necessary? Wnt (talk) 04:36, 28 March 2014 (UTC)


 * That's a handy (if daunting) PDF. I'm not going to have time to work through it properly this morning, but maybe I'll send the link on to school with my daughter. Her teacher wanted to use the tooth as a kind of brain teaser anyway; this way they'll get to learn terms like "transverse groove" and "lateral cusplets" as they go. :) Matt Deres (talk) 11:02, 28 March 2014 (UTC)
 * Wnt's PDF is about identifying fossilized shark teeth from the Neogene period, so I'm not sure how helpful it will be. John M Baker (talk) 13:44, 28 March 2014 (UTC)


 * Since we don't know the tooth's provenance, we really don't know if it is a fossil. Besides, it's a guide for 20 to 3 million years ago, so what's another 20%?  Just looking at the pictures it seems to have something in common with Isurus "first (2nd) anterior tooth" - I think I see the central foramen out of focus in the third photo, and the shape and lack of serration seem similar.  Working back from that it seems like "root lobes round and extend beyond basal limit of crown" describes this tooth better, which is keyed to Alopias; "basal margin of root broadly arched" also seems to fit that (brings us back to 24b "root lobate")  Alas at this point we are back to 23 whether the crown is 'recumbent', which is the sort of glossary term that separates the dilettante from the shark expert.  Good thing we're doing this backwards, eh?  But 16b lateral cusplets unequal - I think this refers to there being one teeny weeny tooth-like extension on one side and not the other (they use this a bit inconsistently in Figure 16B vs. question 1b...); also 15b; 8b is the lack of serration, whew!; and we're back to not multicusped, not notched.  One of these days I'm going to use a taxonomy key the way it's meant to be used, but so far this is about as close as I've come. :)  An image search for Alopias teeth turns up lots and lots of examples, and in the first 50 or so none look exactly like this and few much resemble each other either.  And I'm not confident about how round is "round" and how far the root has to extend so as not to be "beneath" the crown, and above all, that little cusplet isn't turning up in the pictures I'm sorting through.  Maybe it's something else in Lamniformes.  There's still a lot that can be done to try to figure this one out. Wnt (talk) 14:40, 28 March 2014 (UTC)