Richard, and all: Yes, the noble kangaroo is liable to be offended with
me, albeit his dentition is in truth the object of another convention. In
other words, what Richard says about kangaroos (and other marsupials,
including Didelphis) having 4 molars is correct according to the current
and accepted convention, and in saying otherwise I was in error: what I
should have said was that 'no PLACENTAL mammal has more than 3 molars' --
unless, of course, we listen to people who work on Cetacea, who will
remind us that they can't tell how many molars a toothed whale might have,
thanks to their acquired monophyodonty.

All of this, and Richard's question about our use of the term 'deciduous'
for teeth which erupt from alveoli that contain two tooth-buds, must be
answered from a knowledge of serial tooth-replacement. The diagram on p.
230 of Romer's "Vertebrate Body" is taken from a paper by Edmund, although
unfortunately I can't find Edmund in the citations for that chapter
(perhaps somebody here would know the exact reference). Understanding Fig.
222 on p. 232, which shows the 'rolling' development, attrition, and
shedding of teeth in the jaw of a shark, is crucial (ergo standard stuff
on vert. paleo. and comparative anatomy exams).

Romer then presents what is really the same diagram as Edmund's, modified
(simplified) to apply only to mammals; see p. 236, Fig. 231. The caption
says: "One complete set of teeth develops from incisors back to molars.
All of these except the molars, however, are shed .... A second set of
teeth then develops, but never produces molars. Hence the 'permanent'
dentition includes portions of two tooth series" [i.e. Romer means the
'series' of Edmund].

This is an important realization: the molar teeth, erupting as they do
from alveoli containing but a single tooth-bud, are actually just
late-erupting, posteriorly-located teeth belonging to the FIRST series,
i.e. that which in the next more anterior part of the jaw, develops and
erupts the elder tooth-bud in those alveoli which contain two tooth-buds
(i.e. those teeth which we term premolars).

This is all that can be said about it, I think. In my own library, I can
go back as far as H.F. Osborn's 1907 "Evolution of Mammalian Teeth" or his
1912 "Craniometry of the Equidae," or his 1918 "Iconoclastic Type Revision
of the North American Equidae", and find him using the term 'deciduous' to
describe those teeth which are by definition called premolars, that is,
those which develop from the elder tooth-bud in alveoli which contain two
tooth-buds.

I find the same understanding in W.K. Gregory of about the same date, and
in William Diller Matthew's work, as well as in Cope, Marsh, and Scott
already cited in the previous memo. There were disagreements between these
American workers and the great British comparative anatomist Edwin S.
Goodrich, but not about this matter: they all agree that those cheek-teeth
or "grinders" which are replaced are called premolars, and those which are
not replaced are called molars.

In J.S. Kingsley's "Comparative Anatomy of Vertebrates" (1917, P.
Blakiston's & Son, Philadelphia) we get the following helpful information
on p. 226: "Most vertebrates have a succession of teeth (polyphyodont
dentition) and the elasmobranchs show how this has come about [i.e. this
is an allusion to that all-important shark jaw illustration reproduced in
Romer]...."In the non-mammalian classes the number of such dentitions is
indefinite (polyphyodont), but in the great majority of mammals there are
two, the first or milk dentition and the second or permanent dentition
(diphyodont condition)."

The term "milk dentition" or "milk tooth" is an acceptable, although
somewhat informal, synonym of "deciduous dentition" or "deciduous tooth".
Kingsley also uses the very formal "lacteal dentition" = "milk dentition"
= "deciduous teeth". On p. 229, Kingsley says "In mammals....four kinds of
teeth are recognized. These are the incisors in the premaxillary bones,
followed by a single canine at the anterior end of each maxillary bone....
Behind the canines come the premolars (the bicuspids of the dentists)
which have two roots and complicated crowns and appear in both milk and
permanent dentitions. Lastly are the molars, like the premolars in form,
with several roots, but appearing only in the permanent dentition."

On p. 412, Kingsley presents an astonishing diagram, after Rose (umlaut
over the 'o') showing the relationship of each human tooth to the
dentition in the shark. This diagram is a modification and expansion of
Edmund's. The reference is Rose, Entwicklung des Saugethierherzens (umlaut
over the 'a'), Morph. Jahrb., 15, 1890. This implies that the term
"deciduous" must go back rather far, probably at least mid-19th century
(we have previously concluded the same from its use by Cope).

If I had Goodrich better represented in my library -- I possess only Vol.
I, Chapters 1-8, of his monumental treatise comparing the anatomy of
vertebrates -- we would probably find the ultimate answer. Goodrich's huge
opus takes us back to the first decade of the 19th century, and he cites
everybody from Cuvier onward.

Richard has cited Huxley and other very old sources. They are lovely and
interesting, as George Stubbs' 18th-century engravings of dissected horses
are, too; but we no longer use the terminology with which Stubbs labeled
the anatomical parts. So, to cite Huxley for being old or 'first in the
field' so to speak, won't do us any good, because his work antedates
better and more perceptive work -- especially that by Goodrich -- that
came later.

There is, in addition, some reason to suspect that if Huxley referred to
all cheek-teeth as "molars" he may just have been speaking informally in
an attempt to use common rather than technical language -- as we know, he
did a lot of public proselytizing as 'Darwin's Bulldog'. Yet Huxley's
contemporary, V.O. Kovalevsky, the early student of horse evolution who
named Hyracotherium, had a perfectly clear understanding of tooth
development and replacement. It might also behoove us to go back and check
Cuvier, because for all I know his understanding was correct, too; perhaps
someone else can fill us in concerning that.

Above and beyond all this, we should not forget the venerable
International Commmission on Zoological Nomenclature, who review and set
the standards for all anatomical terminology, including that pertaining to
teeth; and their usage of the terms "premolar", "molar", and "deciduous"
is the modern standard which I have been outlining. -- Dr. Deb





> This debate started after Deb described a physical anthropologist as
> confused, because she had insisted on describing a human tooth as a
> 'deciduous molar'.
>
> In my first comment I said that "Deb is following the evolutionary
> position."
>
> To my surprise Deb then denied this, but the more I read her arguments
> the more convinced I am that this is the case.
>
> I am an evolutionist, and would follow the terminology relevant thereto
> if I was, for example, giving the human dental formula in the broader
> context of comparative mammalian anatomy.
>
> But there are two contexts in which we operate - the evolutionary and
> the descriptive. We slip between one and the other in our thinking.
> Terminology in the two contexts differs slightly.
>
> At the descriptive level, as I previously pointed out, the use of the
> term 'deciduous molars' goes back to Huxley. It is unambiguously correct
> in the  context of comparative anatomy within the genus Homo.
>
> Likewise (to refer to a point Terry O'Connor made about consistency) the
> terms 'first/second premolars' make perfect sense in the context of
> descriptive comparative anatomy within the genus Homo. The evolutionary
> terminology of 3rd and 4th premolars makes sense within the context of
> comparative vertebrate anatomy and evolutionary studies.
>
> However I contend that 3rd and 4th premolars is an evolutionary
> terminology that is confusing when applied, at the descriptive level, to
> the jaw of a member of the species Homo.
>
> As an analogy, consider this example. Tetrapods have forelimbs and
> hindlimbs, with each limb carrying a foot. In evolutionary terms, I am a
> tetrapod. I have what can be readily recognised, in an evolutionary
> sense, as forelimbs and hindlimbs. Should I therefore, at the level of
> descriptive anatomy, decline to refer to my arms and hands - in the name
> of consistency?
>
> One thing I missed in your last reply, Deb, was when and why the use of
> the word 'deciduous' (in the sense of shed) teeth was redefined to
> exclude m1 and m2 in humans. You discussed some important evolutionary
> anatomists, but I was wondering whether you had any citation.
>
> One final point. You say "no mammal has more than 3 molar teeth". Should
> I tell the next kangaroo I meet that it is confused if it thinks it has
> a fourth molar? :)
>
> Richard
>
> On 9/10/2012 05:47, [log in to unmask] wrote:
>> 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/
>>>
> <snipped>
>
>
>