Author Topic: Toothless! Loss of Teeth in Returned-to-the-Sea Marine Vertebrates  (Read 194 times)

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Offline Dr Barton

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I just got done listening to SGU episode 700 and the mystery of tooth loss among many marine invertebrates intrigued me. Does anyone have any background for this topic?

It occurred to me that a common factor is salt water. We know that the growing acidity of salt water, due to increased carbonic acid from CO2, is leaching calcium from corals. Is it possible that a similar chemistry affects the teeth of marine invertebrates? They are, after all, the only "bone" exposed directly to the acidic water. If that is the case, then it seems to me that evolution could take one of two paths: lose the teeth, alter the nature of teeth to make them slightly less leachable, or replace them on a regular basis. I believe that there are significant compositional difference between fish and mammal teeth but I am not sure. As for the baleen whales, their baleen is keratin which is, basically, hair and fingernail.

Just wondering if anyone out there has looked into this subject in more detail.

Offline bachfiend

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Re: Toothless! Loss of Teeth in Returned-to-the-Sea Marine Vertebrates
« Reply #1 on: February 27, 2019, 04:36:20 AM »
I just got done listening to SGU episode 700 and the mystery of tooth loss among many marine invertebrates intrigued me. Does anyone have any background for this topic?

It occurred to me that a common factor is salt water. We know that the growing acidity of salt water, due to increased carbonic acid from CO2, is leaching calcium from corals. Is it possible that a similar chemistry affects the teeth of marine invertebrates? They are, after all, the only "bone" exposed directly to the acidic water. If that is the case, then it seems to me that evolution could take one of two paths: lose the teeth, alter the nature of teeth to make them slightly less leachable, or replace them on a regular basis. I believe that there are significant compositional difference between fish and mammal teeth but I am not sure. As for the baleen whales, their baleen is keratin which is, basically, hair and fingernail.

Just wondering if anyone out there has looked into this subject in more detail.

Well, seawater is slightly alkaline, not acidic.  The acidification of the oceans due to increasing atmospheric CO2 is actually less alkalinity.

Loss of teeth is not due to increased acidity of sea water, which isn’t enough - it’s due to teeth no longer being needed (like the loss of eyes in cave dwellers).
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Offline Rai

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Re: Toothless! Loss of Teeth in Returned-to-the-Sea Marine Vertebrates
« Reply #2 on: February 27, 2019, 04:59:23 AM »
Salt Water composition does not explain why only one branch of cetacea lost its teeth while the other (Odontoceti) kept them. Or Pinnipeds, who all have teeth and live in the same salt water.

Offline Dr Barton

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Re: Toothless! Loss of Teeth in Returned-to-the-Sea Marine Vertebrates
« Reply #3 on: March 01, 2019, 07:33:00 PM »
1) Yes, the average pH of ocean water is slightly basic. So, are you saying that the decalcification of coral is not due to a an decrease in pH but to a different cause? That was just my rough understanding of the coral situation. I would like to know the current understanding of the situation.

2) The interviewee of that episode seemed pretty clear (to me) that "lack of need" was considered a candidate in these cases but not a strong candidate. Perhaps I was mistaken in that impression.

3) I thought that the interviewee supported the theory that the common ancestor of both toothed and baleen whales probably was probably a similar-to-Mystibaleen semi-toothless species. That suggests that, in whales, they came to a similar functional bottleneck in tooth evolution and took different paths. The baleens developed a fine keratin structure while the toothed redeveloped teeth.

I took a deeper dive into toothed whales and discovered that their teeth are (if I understood the article correctly) partially to fully without enamel. Many species have, instead, developed the cementum layer of mammalian teeth to provide rigidity to the teeth. To me, this suggested a vulnerability of enamel in the whale's environment. I looked up shark (and some other fish) teeth and found that they often employ enameloid as the outer coating of their teeth. This enameloid refers to a hypermineralized structure. I'm assuming, in reference to mammalian enamel. Over at dugongs, I found that their teeth have a Ca / P ratio of around 3 as opposed to human teeth with a Ca / P ratio of 1.5.

I haven't taken the time to do a much wider search. I did try some further searches but my search terms were not netting me many useful articles. Nevertheless, this small sampling suggests that there is a tooth chemistry issue involved, here. It may be that returned-to-sea marine vertebrates have tooth chemistry issue which that solve in a number of different ways partly driven by functional needs. On the other hand, most cetaceans do not chew but swallow their prey so perhaps lightened functionality (lack of need for crushing pressure) drove a diversity in mineralization patterns. I just hoped that someone, here, had a clearer background on this topic.

https://pubs.rsc.org/en/content/articlehtml/2015/ra/c5ra11560d

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5384008/

https://www.researchgate.net/figure/Comparative-Ca-and-P-content-in-teeth-from-cetaceans-this-study-hippos-data-from_fig2_259002730

https://www.whalefacts.org/what-are-a-whales-teeth-made-of/

 

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