Ptychodus occidentalis

Leidy, 1868


Classification: Elasmobranchii incert. sedis Ptychodontidae

Reference of the original description
Leidy, J. (1868)
Notice of American species of Ptychodus. Proceedings of the Academy of Natural Sciences of Philadelphia, 20, 205–208

Synonyms / new combinations and misspellings
Ptychodus cf. occidentalis

Types
Ptychodus occidentalis
Syntype: ANSP.: 1460; ANSP.: 1461; ANSP.: 1463; ANSP.: 1465;

Images of types

Description:


Citation: Ptychodus occidentalis Leidy, 1868: In: Database of fossil elasmobranch teeth www.shark-references.com, World Wide Web electronic publication, Version 03/2024

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Ptychodus occidentalis Leidy, 1868, syntype, ANSP 1465, near Fort Hays, Kansas © Mike Everhart, Sternberg Museum of Natural History

Description
Original description after Leidy (1868) p. 207 [1414]: Ptychodus occidentalis, n. s.
The Museum of the Academy contains a specimen consisting of the crown of a tooth of a species oi Ptychodus differing from any other previously known. It was obtained by Dr. John L. LeConte, in association with other remains of fishes, from an ash-colored rock of the Cretaceous series, a few miles east of Fort Hays, Kansas.
The tooth is remarkable, especially from the comparatively near approximation of its diameters, the width transversely and fore and aft and the height approaching one another more nearly than in any other species. The forepart of the crown is somewhat injured and the root is broken away. The transverse diameter of the crown at base is 14 lines: the fore and aft diameter has been about an inch: and the height is also an inch. In shape the crown is a blunt cone with the sides sloping evenly to the base and to the posterior sinus. The latter is a triangular concavity about twothirds of the breadth in height.
The direction and arrangement of the ridges of the crown are much like as in the European Ptychodus decurrens, but the principal ridges crossing the crown transversely are finer and the intervals much narrower, indeed the space occupied by a pair of ridges with their interval in P. decurrens would accommodate three ridges with a pair of intervals in P. occidentalis. Descending the sides of the cone the ridges branch as in P. Mortoni, and at the basal half of the crown form a reticulation much as in P. decurrens. At the back of the summit of the crown the principal ridges continue their transverse or parallel course until near the upper part of the. sinus, into which as they descend they are resolved into a fine reticulation. The fore-part of the crown is occupied by a reticulation formed by the descent, convergence and division of the more anterior principal ridges.
From the description it will be observed that the tooth holds an intermediate position in anatomical character to those of Ptychodus Mortoni, and P. decurrens.
Three small teeth, found by Dr. Le Conte in association with the latter, resemble, in their proportions and in the proportionate size and arrangement of the ridges of the crown, the teeth of P. decurrens, but perhaps may belong to the same species as the large tooth above described. The larger of the three specimens is perfect, but has the summit of its crown worn ott'. The crown measures 7 lines transversely, 6 lines fore and aft, and has been from 4 to 5 lines high. The root is 6 lines wide, 41/2 lines fore and aft, and 2 1/2 lines thick. Comparatively coarse ridges cross the crown transversely, curving forward laterally and ending in a marginal reticulation. Branching ridges descend in front from the foremost of the transverse ridges, and likewise end in a marginal reticulation. The sinus is occupied by a finer reticulation joined by fine ridges descending from the summit and sides of the crown. The smallest tooth, likewise perfect, has the crown 4 1/2 lines wide, 3 1/2 lines fore and aft, and 2 1/2 lines high.
Three additional specimens associated with the former ones, are the smallest teeth of Ptychodus I have seen, but I suspect that they belong to the same species. They are transversely ellipsoidal in outline at the base of the crown, and this appears as a low cone elevated at the inner third and with a broad expanding base. The sinus is situated at the inner posterior third. The surface of the crown is crossed with transverse ridges which form a narrow reticulation at the border. The largest of these small specimens is 3 1/2 lines transversely, 1 1/2 fore and aft, and | of a line high from the root. The smallest tooth is 2 1/2 lines wide, 1 1/2- fore and aft, and 1/2 a line from the root.

Remarks
shark-references Species-ID=5381;
valid after Leidy (1868) p. 207 [1414];



References
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