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AN INFORMAL REPORT ON A SCANNING ELECTRON MICROSCOPE STUDY OF A HUMAN-LIKE INCISOR FROM CRETACEOUS STRATA IN GLEN ROSE David N. Menton, Ph.D. St. Louis, MO September 1987 (C) copyright 1991 Missouri Association for Creation, Inc. A recently discovered glossy black fossil tooth in the cretaceous strata near Glen Rose Texas called FSCM bears striking resemblance to a human central maxillary incisor. If this were found to actually be a correct identification for this tooth, it would be difficult to reconcile with current evolutionary scenarios for hominid evolution. Paleontologists at the Smithsonian Institute were understandably critical of the human status of the fossil tooth and concluded after examination that it was a tooth from a class of fossil ganoid fish known as pycnodonts, possibly Sargodon. Several practicing dentists, on the other hand, have concluded on the basis of a gross anatomical and stereo microscopical examination of the fossil that it does indeed bear resemblance to a cross fractured anatomical crown of a human deciduous central incisor. The fossil was loaned to me for three weeks for my evaluation by its discoverer Dr. Carl Baugh of Glen Rose Texas. I am a histologist and not qualified to identify the species of a tooth on the basis of its gross morphology. I understand that I was approached by Dr. Baugh because he believed that I would be unbiased in seeking an identification of the tooth. I first showed the tooth to a dental histologist who concurred with the opinion of other dentists that the tooth grossly resembles a human deciduous maxillary incisor though he felt that the curvature of the cingulum was unusually prominent compared to that of most human teeth. I then showed the tooth to Dr. Frank Winter a physiologist and paleontologist at Washington University School of Dental Medicine who in addition to his familiarity with human teeth has a particular interest in fossil fish teeth (Bradyodonts). Dr. Winter was given no advance information about the tooth other than that it was believed to be a fossil. Winter noticed the black translucent color and architecture of the "enamel" and suggested that it was probably a modified dentine or durodentine of a type found on the surface of the crown of fish teeth. He concluded that the morphology of the tooth was consistent with the marginal incisorform teeth of certain fish (both living and fossil) which are specialized for crushing shelled invertebrates or coral but suggested no specific taxon. According to Winter, most paleoichtheologists largely ignore teeth in their descriptions and classification of fish which might make classification of FSCM difficult. Winter made no comment regarding the specimens human appearance until I asked whether it might possibly be human. He replied that this was very unlikely but that if a ground section of the tooth could be examined in the polarization microscope its relationship to fish or man could be more accurately evaluated. This would obviously be a destructive procedure and as of now, permission has not been granted to do this. I was given permission by Dr. Baugh to engage in a relatively noninvasive examination of the surface microtopography of his fossil in an effort to ascertain whether it is consistent with a human tooth. My specific interest was to examine the tooth in the scanning electron microscope (SEM) for the presence of enamel prisms which are found in nearly all mammals and are relatively distinctive for a group including man, primates, carnivores and some rodents. I felt that the presence or absence of enamel prisms in the fossil could at least confirm whether it is likely to be mammalian or not. Since the enamel of teeth is easily the hardest biological tissue known, it seemed reasonable to expect that it would be preserved in the fossil. The stability of enamel prisms has been confirmed in fossil teeth from a wide range of putative ages. Closely packed "key hole" shaped enamel prisms (as they are viewed on end at the tooth crown surface) are one of the most distinctive features of mammalian teeth and are found in only a few other vertebrates including a few reptiles (both living and fossil but interestingly, not in the "mammal-like" reptiles). Enamel prisms are comprised of many organized hydroxyapatite crystals. Each prism measures approximately 5 microns in diameter and extends in length through the entire thickness of the enamel following a rather sinuous course. In other classes of vertebrates such as bony fish, the enamel or enameloid material, where present, is not prismatic but rather is comprised of large hydroxyapatite crystals that are uniformly arranged near the surface of the tooth and are often more random in architecture in the deeper tissue. Pycnodont teeth are known to lack enamel on or near their incisal surface and instead have a superficial layer of modified dentine (Peyer 1968) which is both apatitic and fibrous and thus should be distinctively different in its appearance than enamel. Since FSCM is said to closely resemble a human deciduous maxillary central incisor by dentists and to resemble the incisorform marginal teeth of a fish like a Sargodon by paleontologists, the purpose of this study was to compare the fine structure of the superficial hard tissue of FSCM with that of an appropriate tooth from both man and fish. An incisorform tooth from a sheepshead fish of the genus Sargus was used for comparison as no fossil tooth of Sargodon was available. This seemed useful, none the less, as Sargodon was named after the living genus Sargus because of the similarity of both the gross and histological structure of its teeth. No attempt was made to actually classify the taxon of FSCM but merely to see whether the enamel of FSCM is more like that of Homo or Sargus. Preparation of tooth specimens for scanning electron microscopy: The specimens examined in this study consisted of the fossil tooth FSCM found in cretaceous strata near Glen Rose Texas, a modern deciduous human maxillary central incisor (not a fossil) and an incisorform fish tooth from the living genus Sargus known as a salt water sheepshead (courtesy of Dr. Frank Winter of Washington University School of Dental Medicine). All specimens were etched in 2% hydrochloric acid for 2 minutes except the Sargus tooth was etched for 1 minute. The tooth fossil was also scrubbed on its incisal surface with a cotton applicator dipped in toluene prior to etching in an effort to remove a heavy acrylic coating and was lightly ground on a small portion of its incisal surface with a fine carborundum cloth. All specimens were then glued to specimen studs and stored in a desicator. Prior to examination in the scanning electron microscope (SEM) each specimen was lightly ion etched for 30 seconds at 5 amps in a Denton Desk-1 triode sputter unit to remove any surface volatiles followed by a sputter coating of approximately 30 angstroms of gold to produce an electrical conductive surface. The specimens were examined in a Philips 501 SEM and all photographs were taken on Polaroid type 52 directpositive film at a magnification of 1,250 X. All specimens were photographed on or near the incisal surface at an angle of about 40{o} as viewed from the medial surface of the tooth, the labial surface of the tooth is in each case to the left of the photographed field and the lingual surface to the right. Observations: Figure 1250/10 Human maxillary central incisor (deciduous)- The incisal surface seen here reveals a mosaic field of "key hole" shaped enamel prisms measuring about 5 micrometers in diameter (note 10 micrometer bars at bottom of photo). The prisms are separated by a more deeply etched interprismatic region. The prisms have the staggered arrangement typical of human teeth near the enamel surface. The enamel prisms are comprised of hydroxyapatite crystals which measure about 40 nanometers in width and over 150 nanometers in length and are below the resolution of these micrographs. X 1,250, Bars = 10 micrometers Figure 1251/10 Fossil tooth FSCM - No trace of a mosaic appearance or enamel prisms are found in this specimen. The tooth appears to be comprised of randomized apatitic crystals and fibrous elements, possibly collagen fibrils. This is consistent with the modified dentine that covers much of the crown of pycnodonts such as Sargodon. X 1,250, Bars = 10 micrometers Figure 1252/10 Fossil tooth FSCM - This is from an area that was lightly ground with carborundum cloth. The architecture here is not greatly different from that of the previous photo. Neither of these photos bears any resemblance to that of the human enamel in figure 1250/10 above. X 1,250, Bars = 10 micrometers Figure 59/10 Tooth from sheepshead, Sargus (species unknown) The woven and apparently fibrous nature of this modified dentine is similar to that of the fossil tooth FSCM (though somewhat coarser in appearance) but quite unlike that of the human tooth. This field is on the labial surface adjacent to the incisal surface. X 1,250, Bars = 10 micrometers Conclusions: The lack of enamel prisms in FSCM does not support the human status of this fossil tooth but neither does it give us a clear indication of its specific taxon. It is highly unlikely that FSCM had a prismatic enamel architecture in life which was subsequently lost by the fossilization process in view of the hardness of enamel crystals and the excellent preservation of detailed morphology in the fossil specimen. Gantt (1982) has described enamel as the "only tissue which is virtually fossilized before death." The architecture of the incisal surface hard tissue of FSCM has a woven fibrous appearance like that of Sargus but the latter is of a coarser structure. It should be emphasized that whereas enamel is almost entirely mineral in structure, dentine has a significant organic component much of which is the fibrous protein collagen. The fibrous component of FSCM then is entirely incompatible with true enamel quite apart from its lack of enamel prisms. While these observations seem to exclude the possibility that FSCM is human they do not necessarily allow us to conclude with complete confidence that it is a pycnodont fish. Still, other than among certain fish, there are no other teeth found in nature that are so similar in gross morphology to the human incisor and yet have modified dentine on their incisal surface. The "enamel" (modified dentine?) of FSCM while not virtually identical to Sargus is similar in several important respects. It would, of course, be interesting to examine one of the existing fossil marginal teeth of Sargodon itself in the SEM but to my knowledge this has never been done. The cretaceous formation in GlenRose is believed to be marine and this would further support the possibility of this specimen being the tooth of a ganoid fish. Moreover, if FSCM is a fish, there should be a high probability of finding more specimens which would permit a more destructive analysis of its chemistry and microarchitecture. Human deciduous teeth, on the other hand, are literally temporary teeth as anyone knows who has tried to save one for any number of years, and thus are rarely found as fossils. Finally, the marginal (incisor-like tooth) of the fossil fish Sargodon tomicus has been studied in some detail by Plieninger (see Payer 1937). The marginal tooth shown in text figure 25 of this book bears a striking similarity to FSCM. More importantly, Plieninger's description (in German) provides some very interesting observations. Plieninger describes the tooth as being comprised of two distinct parts, a mat surfaced base and a glossy black (!) crown. He commented that the crown is often fractured from the base in fossil specimens. He even stated that the crown of the tooth has a strong similarity to the upper deciduous incisor of man! He also described facets on the lingual surface of the teeth near the incisal edge but these were more punctuate in his specimen. I must conclude that it is now inappropriate to claim that fossil FSCM is a human incisor. It is an unusual and interesting specimen and merits further study as to the organism it represents. References cited: Gantt, David G., 1982 Neogene Hominoid evolution A tooth's inside view. In:Teeth: Form, Function, and Evolution, Bjorn Kurten editor, Columbia University Press, New York pp 95-107 Peyer, Bernhard, 1937, Die Triasfauna der Tessiner Kalkalpen, Kommissionsverlag von E. Birkhauser & Cie, Basel pp 29-33. Peyer, Bernhard, 1968, Comparative Odontology, The University of Chicago Press, Chicago.


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