Worn and unworn Camarasaurus teeth in the collections at Dinosaur National Monument
November 2, 2019
Unworn:
Worn:
Spent some time last week just admiring these things. They’re pretty cool.
EDIT: in answer to Mike’s question in the first comment below, here’s a photo of some more worn teeth, showing that the level of wear in the one shown above is not unusual. Also, all of these worn teeth still had full roots, with no sign of the root resorption that would have preceded shedding of the tooth, so they were evidently going to be used for a while yet, probably a few months at least — BUT see the very useful comment from Jens Kosch below on the likely rapidity of tooth replacement in Camarasaurus.
Sauropod Vertebra Picture of the Week 
November 2, 2019 at 8:32 am
That is a ton of wear. How certain are you that it’s natural, healthy wear, and not breakage? Are the multiple teeth with that same dramatic wear pattern?
November 2, 2019 at 4:25 pm
Yeah, all the worn teeth look pretty much the same, with comparable asymmetry and the same weird ‘corner’ where the ?two wear facets meet. I will update the post with a photo showing this.
November 2, 2019 at 6:48 pm
Well, that is crazy. Never appreciated this before. Thank you!
November 3, 2019 at 8:46 pm
First off all: those teeth are really cool, I can never see enough of them.
Form my experience looking at Camarasaurus (and some other macronarian and a few turiasaur teeth) I can say those are really typical wear facets.
That little corner is rather typical for an area where two wear facets meet. I saw the same on Giraffatitan and Europasaurus for example (although those have three wear facets, adding a distinct appical one to the mesial and distal ones). Eventually in even later wear stages those corner do get smoothed out, but it i the last stage of wear after the merging of wear facets.
As for them being used for at least a few month because there are no signs of resorption on the roots: That seems like you underestimate the replacement rate in Camarasaurus. I looked at the CT scans of multiple camarasaurs and and calculated the replacement rate based on the incremental growth line (von Ebner line) spacing found in histological sections (D’Emic et al. 2013) and found replacement average replacement rates in the 50 to 70 days range.
Don’t forget that the replacement teeth spend most of their growth deeper in the “crypts” of the alveolar ramus neatly stacked up (usually two, rarely three replacement teeth in Camarasaurus). They actually drift a a bit down in their movement to the labial position from their origin near the replacement foramen on the lingual side of the crypt/alveolus before they push up. I saw some cases in Camarasaurus where the replacement tooth had not invaded the pulp cavity at all when the tooth length suggested that the functional tooth would be shed in only a few weeks (spcially in more distal alveoli). At most they had caused barely identifiable resorption on the lingua side of root (in contrast in Giraffatitan the replacement teeth seem to always invade the pulp cavity of the functional tooth [in USNM V 5730, the presumed Brachiosaurus skull there are no functional teeth preserved in situ to compare …] and in Diplodocoids the replacement teeth normally simply don’t invade the pulp cavity, so root resorption starts very late in replacement).
All in all I would say those worn teeth are unlikely to used for more than two more months, probably a lot less.
November 3, 2019 at 8:55 pm
Wow, Jens, thank you, that is all extremely interesting and useful stuff.
November 4, 2019 at 5:00 am
Just wondering: if the tooth microwear is even, don’t we expect a smooth(ened) crown? Instead, these “weird corners” look like they were deliberately chipped away due to the underlying design of the tooth microstructure/fracture line propergation to try to maintain a sharp crown (i.e. still useful tooth wherefore the roots were not absorbed/prepared for shredding yet). It eeriely looks like the edge of stone age flakes/tools (…getting tongue tied here, what’s the exact word for those?)
November 4, 2019 at 5:30 am
I can see where you are coming from with that idea, Leo, but the answer for the shape of the macro wear (and why it forms individual facets) is even simpler in this case: They are formed by attrition, tooth-tooth contact by occlusion. So we would not expect a smooth crown with even wear all over it, but rather individual parts in the area where the opposing teeth contact it being worn away.
Other facets (for example the apical facets in Giraffatitan) can be formed by abrasion (tooth to food contact). Those only form in response to almost stereotypical movements of food over the same spots again and again (like stripping or pulling movements that send flexible branches of parts of leafs scratching over parts of a tooth).
However, I think you are on to something when you say the underlying design tries to maintain a useful tooth with wear features. That Is something I would like to look into in the future, because I see small “shoulders” formed by enamel flanking the dentin core in a facet and I would love to see if that arrangement is as good or even better at some tasks like cropping or holding onto a branch during a pulling motion as “fresh” tooth (with intact carinae if it has them) is.
November 4, 2019 at 6:33 am
This is pretty much the conversation that Brian Engh and Yara Haridy and I had in collections while looking at these teeth: were parts of them “built to fail” to produce such a distinctive — and possibly useful — wear pattern? It would not surprise me. A vast number of things in biology only attain their final and most useful form after they’ve interacted with the environment. I need to do a whole post on that sometime.
November 4, 2019 at 9:06 am
A huge thankyou to Jens for this fascinating and novel (to me) information.
Jens, a follow-up question: it seems the erosion rate for these teeth is fantastically fast: I guess they lose a centimeter or more during their fifty-to-seventy-day life, so are they really wearing down a fifth of a milimeter per day? If so, are they made from some completely different material from human teeth, which last fifty to seventy years?
(Yes, I should know this stuff; and even given that I don’t, I should be sufficiently ashamed of my ignorance to avoid parading it in public. But my experience has been that the way I got to know the things I do know was mostly by admitting my ignorance about those things, so I’m sticking with that strategy.)