243 
OSTEOLOGY OF POLYGLYPHANCDON—GILMORE 
series, a style of dentition never before observed in the Sauria, either 
living or extinct (see figs. 19 and 21). These teeth display a sharp 
transverse cutting edge, with a subtriangular cusp on the outer edge 
in both upper and lower teeth. There is no indication of median 
cusps, as in the teeth of Diadectes or Trilopho- 
saurus, to which these teeth have a resemblance in 
their great transverse width. This smooth, sharp- 
edged crown is smoothly beveled on both sides of 
the cutting edge. The sides of the teeth swell out 
and then contract sharply to the root. The lower 
teeth fit between the upper teeth when the jaws are 
closed, thus closely interlocking. 
The anterior teeth in external view are conical, 
but on the inner side the crowns are slightly exca- 
vated dorsoventrally on each side of an incipient 
median ridge (see C and D, fig. 22). This vertical 
ridge grows progressively more prominent in a pos- 
terior direction. On the eighth lower tooth (fig. 
21) and seventh upper tooth, it suddenly extends 
Ficure 22.—Lower 
teeth of Polygly- 
phanodon sternber- 
gi Gilmore, U.S. 
N.M. No. 15568, 
all five times natu- 
ral size: A, Four- 
teenth tooth, enu- 
merated from the 
front, lateral view; 
B, same, top view; 
C, fourth tooth, 
internal view; D, 
laterally into a sharp cutting edge on the crown, the 
whole crown being about one-half the width of the 
next tooth posteriorly. The succeeding teeth grow 
progressively wider, reaching the maximum size on 
the tenth. Those following remain constant in di- 
ameter as far an the seventeenth, which is percepti- 
bly narrowed. The last or eighteenth tooth in the 
maxillary and the last or nineteenth tooth in the 
dentary are greatly reduced and conical, with faint 
inner vertical ridge. 
The complete dentition of Polyglyphanodon as indicated by the 
type specimen shows the dental formula to be as follows: 
same, top view. 
maxillary 18, premaxillary 3 = 42 
dentary 19 33 
The teeth are heterodont and anchylosed to the jaw bones in shallow 
pits that are regarded as subacrodont in character of implantation. 
These shallow depressions for the teeth in no way correspond to the 
alveoli of the typical thecodont attachment but are more like those 
of the Amphibia. There is no uniformity of opinion as to what 
kind of tooth insertion is oldest in the Sauria. The fossil record 
seems to indicate that thecodonty has preceded both pleurodonty and 
acrodonty, as pointed out by Camp.* The teeth are solid, and in none 
of the specimens is there evidence of replacement teeth. 
4Camp, C. L., Classification of the lizards. Bull. Amer. Mus. Nat. Hist., vol. 48, p. 
364, 1923. 
