Interesting lower GW tooth from Peru

[britishcanuk]

I picked up this interesting Peruvian GW tooth. It looks like some minor damage, but upon closer inspection it appears to be part of its natural morphology. Looks like a transitional tooth, thoughts?

[britishcanuk]

Here's another lower tooth, this time a mako. I believe that it too has the very beginnings of a wavy edge that precluded the serrations seen on later hubbelli and carcharias. 

[sagacious]

Re the first post: Certainly a very nice tooth.  I do not have any lower transitional Carcharodon teeth that are uniformly wavy along the edge from the base of the crown to almost the very tip.  Those in my collection generally show a trend of variable serration size near the base of the crown, with serration size decreasing quickly apically.  However, I see quite a bit more variation in the serration of the lower transitionals than the uppers from the same layer.  I don't see a lot of focus on studying the transition in the lower teeth, perhaps because that variability may somewhat 'wash-out' the study of the development of serrations along the edge.

 

Precise provenance data would help here.  It doesn't look fully-modern in terms of serration, but that waviness and what appears to be a slight pathology on the lower edge of your last photo in the first post, leave me with some question as to what degree of pathology is reflected in the serrations.  I assume these are larger teeth, but I generally see less 'pointed' serrations on lowers from immature C carcharias and C hubbelli, so a size would help in shedding some light on that aspect.

 

Re your second post: I think you maybe meant to say, "Here's another lower tooth, this time also Carcharodon."

[britishcanuk]

Thanks for your thoughts sagacious. They are probably about 1.5"+ each. Unfortunately I don't have any more collection data other than just the country they came from.

 

I wonder, would you label the top tooth a great white or hubbelli? I'll label the bottom tooth hastalis, but at what point does one need to consider calling it hubbelli?

 

Id be interested in seeing some of your transitional specimens.

 

cheers!

[sagacious]

On ‎5‎/‎9‎/‎2017 at 4:50 PM, britishcanuk said:

Thanks for your thoughts sagacious. They are probably about 1.5"+ each. Unfortunately I don't have any more collection data other than just the country they came from.

 

I wonder, would you label the top tooth a great white or hubbelli? I'll label the bottom tooth hastalis, but at what point does one need to consider calling it hubbelli?

 

Id be interested in seeing some of your transitional specimens.

 

cheers!

bc,

 

The label you put on your specimens is always provisional, and can always easily be changed.  At this point, considering the provenance status of the tooth, the most accurate identification would probably be Carcharodon cf. hubbelli.  That ID acknowledges that the tooth is thought to be hubbelli, but that the ID cannot 100% rule out a pathologic tooth of C carcharias.  Peruvian teeth do not always look exactly the same as transitional Carcharodon teeth from other areas, such as California, so if you see more lower teeth with that full-length 'wavy edge' from Peru, then that may be the norm, or just a slight variation, for hubbelli from that location.  When I see waviness in teeth here in CA, it's very minute waviness, much like your second tooth.  I don't see teeth here with that larger-scale waviness along the entire edge.

 

You don't specify where/when the second lower tooth is from, but considering the minute waviness of the edge, one wonders if upper anterior teeth from the same animal would not have shown more definite (larger) serrations.  If so, then for time-averaged layers in formations spanning about 8-6Ma, in some cases isolated upper teeth from conspecifics might possibly be identified as C hubbelli, and lower teeth as C hastalis.  I occasionally find myself facing that possibility.

 

Not everyone will agree, but for practical purposes of discerning transitional teeth at this level, if you can feel definite serrations when running your fingernail over the edge of the tooth, then that distinguishes hubbelli from hastalis.  The species difference here is based partly on the developing trend of functional serrations, and if your fingernail can feel the serrations, then the serrations are becoming functional.  I have teeth that show some very minute waviness, but except for some super tiny wear-nicks on the edge, you can't feel the serrations.  I consider those teeth C hastalis.

 

One the other end of the spectrum, if the serrations go from the base to the very tip of the tooth, and they're the same size (or nearly) as extant great whites, and the serrations are perpendicular to the edge (or very nearly), then I consider those teeth C carcharias. 

 

The tooth below is 1.71" and is typical in characteristics of the C hubbelli  lower teeth I see here around Capitola.  The serrations are minute but visible, do not extend quite to the very tip; and if you look closely the serrations are not perpendicular to the edge like a modern great white, but are instead angled toward the tip at about 30-35 degrees. 

 

Regards,

Eric