 |
 |
To reply to both Richard and Terry concerning the terminology for teeth -- first, as to Richard's question as to 'how far back' does the correct usage of 'molar', 'premolar', and 'deciduous' go -- the answer is that among vertebrate paleontologists, it goes back to when the embryology of teeth was figured out in the middle of the 19th century, so that by the time of the publication of William King Gregory's comprehensive two-volume "Evolution Emerging" (1951, MacMillan & Co.), he could refer to the "Cope-Osborn theory of dental formation". This takes us back to all the works of Henry Fairfield Osborn, which span from about 1880 to about 1920, in which the terminology is used correctly along with discussion of the "tritubercular theory", which allows us to trace the identity not only of the various teeth but the cusps of the teeth. Their work was contemporary with that of another excellent paleontologist, William Berryman Scott, whose still-relevant textbook "A History of Land Mammals in the Western Hemisphere" (1913, MacMillan) also uses tooth terminology correctly. To take it the last step back, we have the brilliant (my hero) Edward Drinker Cope, and my fellow K.U. man Samuel Wendell Williston. Cope's prolific output came in the 1860's through 1880's, along with his famous rivalry -- the "bone wars" -- with Othniel C. Marsh. Williston was active a little later, during the 1880's and 1890's. All of these men used the tooth terminology correctly. Now, the correct usage of the term "molars" as meaning "teeth that are not replaced" or "teeth that come from an alveolus that only develops one tooth-bud" is crucial to our being able to "count" the teeth, in other words to write the correct tooth-formula, for any mammal. The really difficult ones are those that have reduced dentition, i.e. for example sloths or cats, and those that have more teeth than occur in a 'normal' or 'standard' placental, i.e. more than I3, C1, P4, M3. Thus in working with an opossum, for example, the safest thing to do is to count forward from the last molar, because no mammal has more than 3 molar teeth, so that any tooth that has more than one cusp that lies ahead of the 1st molar (that is the third one counting forward from the back) but behind the canine is likely a premolar. Of course, if we were working with a newly-discovered species rather than a well-known one like Didelphis virginianus, we would ideally like to get a series of juveniles in order to XRay their jaws in order to confirm which of the alveoli contain permanent premolars developing beneath the deciduous ones. Likewise, it is very helpful to know that across the whole of the Carnivora, the carnassial teeth are superior P4 over inferior M1 in the permanent dentition. Especially in cats, where most of the molars do not develop, this will assure correct identification of all the teeth. Of course, again, we know this because embryological and/or XRay studies prove which alveoli contain two tooth-buds and which contain only one. So well-established is this understanding of tooth terminology/tooth embryology, that for example on p. 363 of Scott's 1913 textbook there is an illustration of the dentition of the Collared Peccary in which only I3/3, C/C, P2/2, and M1/1 are labeled. Having done this, the rest of the teeth do not have to be labeled. Gregory's "Evolution Emerging" is contemporary with the old standard Vert. Paleo. textbook, which is Alfred Sherwood Romer's "Vertebrate Paleontology" (with the first edition in 1933, Romer continued to update it with new editions, reflecting new finds, until the mid-1970's). His "Vertebrate Body" that I have already cited in a previous memo in this thread contains an excellent explication of the development of the mammalian skull, tritubercular theory, and standard tooth terminology. The other branch of natural science which naturally concerns itself with this business is Mammalogy, and the best-used textbook there is the one by Terry A. Vaughan (1972 and later editions, W.B. Saunders & Co.). There is an excellent illustration on p. 17 of my 1972 edition showing skull parts and tooth identities, and the discussion of tooth and cusp evolution and identity (largely taken from Romer) spans pp. 18-21. Now, as to Terry's query about whether we can ever hope to get human dentists to refer to the human premolar teeth as P3/3 and P4/4, the answer to that is no -- because human dentists are in this game for quite different reasons than we zooarchaeologists are. There are numerous different systems for numbering teeth (look in Ash's "Wheeler's Dental Anatomy, Physiology, and Occlusion" 1993, W.B. Saunders if you want to see all of them). The reason for the existence of each of these systems is to facilitate communication between professionals working on the teeth. In human dentistry, the widely-used Palmer system of notation first thinks of a person's head facing toward the dentist. Then the system divides the tooth-bearing parts of the skull into four quadrants, which are numbered with Roman numerals, left upper I, right upper II, right lower III, left lower IV (going clockwise around the 'muzzle'). It then numbers the teeth beginning with the central incisors, 1 through 8 (or more). For example, the maxillary right first molar is designated II-6 (or sometimes just "6"). Analogous to this we have the Williams system of notation in equine dentistry, which works the same way. By this system, a horse's right superior canine tooth is called II-4, its right inferior 2nd premolar III-6, and its left superior 2nd molar is I-10. Both of these systems completely ignore what we know about the evolution and embryology of teeth, and thus completely obscure it. I find that many equine dentists indeed know very little about how teeth got to be where they are or how they came to have the form they have in whatever species; and for this reason I find much confusion among them when there is an anomaly such as a supernumerary tooth, a dentigerous cyst (an 'ear tooth'), or a twinned tooth. Nor have they any knowledge of cusp nomenclature or the development of hypsodonty or lophodonty. But, you see that it does not really have to matter to them, because their job is not to explain teeth but to treat or extract them. Nonetheless I do consider the system that we use, i.e. where the basic placental tooth formula is dI1-3, dC/C, dP1-4 followed by I1-3, C/C, P1-4, M1-3 to be superior, and I would strongly advocate its continued use at least among mammalogists, vertebrate paleontologists, physical anthropologists and zooarchaeologists. The reason I consider it superior is that it does not preclude us from understanding the simpler 'functional' numbering systems used by dentists, while allowing us insight as to how teeth develop and what might go wrong with the normal developmental sequence. I want to close by highlighting something that Terry mentioned, that some wellknown, influential, and otherwise excellent teacher of physical anthro. consistently mis-used the term 'molar', i.e. he used it in the vernacular sense, which terms any tooth behind the canine a 'molar' because all such teeth are (more or less) 'grinders' in humans. This is the usage of the farmer, rancher, and countryman. As I mentioned in an earlier memo, I have seen this error or 'sloppy language' from some others, particularly in equine dentistry. Vernacular usage is not wrong any more than vernacular usage of other words is 'wrong'; but it becomes dangerous when the teacher himself does not know any better, because it will get students who want and need a perfectly clear understanding into trouble. One of my maxims is that "sloppy language implies muddy thinking". Even the human dentist does not refer to the premolar teeth as 'molars' except possibly in casual conversation with a patient whom he thinks cannot understand anything more technical. With the better-educated patient he may go into 'unicuspids', 'bicuspids', and 'tricuspids', which is also rather an undefined, and certainly an antique, terminology. I think that we are best off being careful to use the terms 'premolar' and 'molar' as correctly as our forebears Cope, Marsh, Williston, Osborn, and Romer have taught.-- Dr. Deb > Well, since you raise the subject.... > > I am with Deb on this one. Granted the term 'molar' has taken quite a > range > of meanings over the years, both technical and vernacular, and yes, > Cornwall (who got me started in animal bones) used to talk about > 'deciduous > molars', but then he was always more at home with bones than with teeth. > We > accept that some terms that are in vernacular use may have a more > restricted technical definition: 'soil' is a good example. Defining molars > by their 'grinding' function has a sort of logic when applied to people > and > badgers, though less so when applied to horses (in which the premolars do > just as much grinding) or cats (in which the few molars do not grind at > all). So an ontogenic definition, by which premolars have a deciduous > precursor and molars *sensu stricto* are only present in the permanent > dentition, seems to me to make an important distinction and to be worth > maintaining. > > And while we are at it, can we persuade our human osteo colleagues (and > dentists) to stop referring to the human premolars as 'first/second > premolars'? We Old World primates have only 3rd and 4th premolars in each > quarter-jaw, having got rid of the 1st and 2nd long, long ago in an > evolutionary clade far away. Even the prosimians lack a 1st premolar, and > I > like to think that I am somewhat derived relative to an Eocene notharctine > primate. > > So what do you think are our chances or getting consistent dental > terminology into physical anthropology? > > Terry > > > Terry O'Connor > Professor of Archaeological Science > Department of Archaeology, University of York > Biology S Block, Heslington, > York YO10 5DD > +44-1943-328619 > http://www.york.ac.uk/archaeology/staff/academic-staff/terry-oconnor/ > > And see the blog at > http://zooarchatyork.wordpress.com/author/zooarchatyork/ > > > > On 6 October 2012 08:07, <[log in to unmask]> wrote: > >> Ahh, well, Richard, it's gallant of you but of course you don't have to >> come to the defense of anyone, because no one has been attacked. >> >> I probably did fail to make myself clear, however. The tooth in question >> was a human second lower molar or m2. In my conversation with the >> 'confused' person, I was not speaking from some old-fashioned theory of >> the evolutionary origin of that tooth, or any tooth, but merely stating >> the correct fact that this tooth is one of two in each rear quarter of >> the >> human jawbone that are not replaced. It therefore can in no sense be >> "deciduous". To repeat: there is no such thing as a "deciduous molar"; >> it >> is impossible by definition, because the only deciduous teeth are by >> definition premolar, canine, or incisor teeth. That the tooth in >> question >> is not replaced -- in other words, it develops in and erupts from a >> 'one-tooth alveolus' -- is what defines this tooth as a molar in the >> technical (as opposed to the vernacular) sense. >> >> Your response prompted me, of course, to go back to my library to check >> a >> reference or two, and the happy result is that I am able to report an >> error on p. 46 of the otherwise very helpful book "Teeth" by Simon >> Hillson >> (Cambridge Univ. Press). The error is in Fig. 1.25, which shows >> deciduous >> and permanent teeth in Homo. The error is that the labels for the lower >> teeth have been switched -- i.e. the label that says "permanent lower" >> actually shows the deciduous lower arcade. The labels for the deciduous >> and permanent upper arcades are correct. >> >> The tooth formula given on p. 44 of this book for humans is correct: >> >> di2/2, dc1/1, dp2/2 ----> i2/2, c1/1, p2/2, m3/3 >> >> ....and this is what, as I said before, I was trying to help my physical >> anthro colleague to understand. Also as I said before: I sympathize, it >> is >> easy to get mixed up. -- Dr. Deb >> >> >> >> > This is off topic, but let me come to the defence of the physical >> > anthropologist that Deb conversed with. >> > >> > The anthropologist spoke of a human tooth as a 'deciduous molar'. >> > >> > Deb says she told the "confused" anthropologist that there are no >> > deciduous molars. >> > >> > In saying this, Deb is following the evolutionary position that the >> two >> > human molariform teeth are adaptively evolved from premolars. >> > >> > I want to make the point that the physical anthropologist, in terms of >> > nomenclature, was by no means confused. She is in step with functional >> > terminology widely used by English speaking physical anthropologists - >> > and dental anatomists, clinical dentists, orthodontists, etc.. >> > >> > The two deciduous grinding teeth are called 'molars', whatever the >> > evolutionary origin of these molariform teeth might be. >> > >> > Richard >> > >> > >> > On 5/10/2012 05:58, [log in to unmask] wrote: >> >> [snipped] >> >> >> >> I go into this a little because it's a subject dear to my own heart; >> I >> >> am >> >> currently writing a textbook on equine dentistry, which I have been >> >> researching for years. I have a great admiration for all >> >> zooarchaeologists >> >> but I also know, from talking with some anthro/archaeo graduates, >> that >> >> they can be mixed up about some things. For example recently I had to >> >> demur (for the sake of peace) in a conversation in which someone >> trained >> >> in physical anthropology insisted to me that a certain human tooth >> >> represented a 'deciduous molar'. She is confusing 'molar' in the >> sense >> >> of >> >> 'cheek tooth' with 'molar' in its technical sense, i.e. molar vs. >> >> premolar. When I told her there are no deciduous molars, that only >> the >> >> premolar teeth are replaced, or again that there are 'one-tooth >> alveoli' >> >> vs. 'two-tooth alveoli', she was surprised and confused because she >> also >> >> has muddled the term 'pre' in 'premolar', confusing 'pre' meaning >> >> anterior >> >> in TIME with 'pre' meaning anterior in POSITION. I sympathize; it is >> >> easy >> >> for anyone to get mixed up when the information presented in most >> >> existing >> >> textbooks fails to convey an adequate mental picture. -- Dr. Deb >> >> >> >> >> > >> > >> > >> >