Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/906/
896 
TEETH. 
Fig. 572. 
Teeth in different stages of formation from one 
alveolus of the Gavial: a is the base partly 
absorbed by the pressure of b, the successional 
tooth ; below which is figured c, the germ of the 
next tooth to follow. 
Amongst the remains of Crocodilians which 
are scattered through the Tilgate strata, the 
most common ones are detached teeth, from 
the difference observable in the form of which, 
Dr. Mantell has observed, that “ they appear 
referable to two kinds, the one belonging to 
that division of crocodiles with long slender 
muzzles, named Gavial, the other to a species 
of Crocodile, properly so-called, and resembling 
a fossil species found at Caen.”* 
Dr. Mantell has obligingly communicated 
to me figures of well-preserved specimens of 
both the forms of teeth alluded to, the exact¬ 
ness of which I have recognised by a com¬ 
parison with the specimens themselves in the 
British Museum. 
The tooth which, from its more slender 
and acuminated form, approaches nearest to 
the character of those of the Gavial, presents 
a marked difference, however, from the teeth 
of any of the recent species of that sub-genus 
of Crocodilians, as well as from those of the 
long and slender-snouted extinct genera, 
called Teleosaurus, Steneosaurus, &c. I have 
described itj", therefore, as indicative of a 
distinct species, under the name of Crocodilus 
cidtridens. The crown is laterally compressed, 
subincurved, with two opposite trenchant 
edges, one forming the concave, the other the 
convex, outline of the tooth. In the Gavial, 
the direction of the flattening of the crown 
and the situation of the trenchant edges are 
the reverse, the compression being from be¬ 
fore backwards, and the edges being lateral.% 
* Wonders of Geology, 1839, vol. i. p. 386. 
+ Odontography, pi. lxii. a, figs. 9, 10. 
t The tooth attributed by M. Deslongchamps 
to the Poikilopleuron, agrees in form with those of 
The tooth of the Crocodilus cidtridens thus re¬ 
sembles in form that of the Megalosaur, and 
perhaps still more those of the Argenton 
crocodile ; but I have not observed any spe¬ 
cimens of the Wealden teeth in which the 
edges of the crown were serrated, as in both 
the reptiles just cited. The teeth of the Cro¬ 
codilus cidtridens also present a character 
which does not exist in the teeth of the 
Megalosaur, and is not attributed by Cu¬ 
vier to those of the Crocodile d'Argenton. 
The sides of the crown are traversed by a 
few longitudinal parallel ridges, with regular 
intervals of about one line, in a crown of a 
tooth one inch and a half in length : these 
ridges subside before they reach the apex of 
the tooth, and more rapidly at the convex 
than at the concave side of the crown. 
Hitherto these teeth have not been found 
so associated with any part of the skeleton 
of the same species as to yield further cha¬ 
racters of the present extinct Crocodilian ; 
but from the above-mentioned well-marked 
differences between these teeth and those of 
all the existing species, it is most probable 
that the extinct crocodile formed the type of 
a distinct sub-genus, for which the term Su- 
chosaurus has been proposed. 
The second form of tooth having the gene¬ 
ric characters of those of the crocodile, which 
has been discovered in the Wealden and 
approximate strata, is as remarkable for its 
thick, rounded, and obtuse crown as the teeth 
of the preceding species are for their slender, 
compressed, acute, and trenchant character. 
It consequently approaches more nearly to 
the teeth which characterise the broad and 
comparatively short-snouted crocodiles ; but 
it differs from these in one of the same cha¬ 
racters by which the tooth of the Suchosaurus 
cultridens differs from those of the Gavials, 
viz., in the longitudinal ridges which traverse 
the exterior of the crown. These are, how¬ 
ever, more numerous, more close-set, and 
more neatly defined than in the Suchosaurus 
cultridens. Two of the ridges, larger and 
sharper than the rest, traverse opposite sides 
of the tooth, from the base to the apex of the 
crown ; they are placed, as in the crocodile 
and Gavial, at the sides of the crown, midway 
between the convex and concave lines of the 
curvature of the tooth. These ridges are 
confined to the enamel ; the cement-covered 
cylindrical base of the tooth is smooth. The 
size of the teeth varies from a length of crown 
of two inches, with a basal diameter of one 
inch and a half to teeth of one-third of these 
dimensions. I have proposed to call this 
extinct crocodile, with biconcave vertebrae, 
Goniopholis crassidens. 
Development. — In the black alligator of 
Guiana the first fourteen teeth of the lower 
jaw are implanted in distinct sockets, the 
remaining posterior teeth are lodged close 
together in a continuous groove, in which the 
divisions for sockets are faintly indicated by 
vertical ridges, as in the jaws of the Ichthyo- 
the Gavial, and differs in the characters cited in the 
text from those of the Crocodilus cultridens.
        

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