Teeth with the crown more or less elevated and overhanging, ornamented with transverse or radiating ridges, and surrounded by a larger or smaller, finely marked area. Surface of root smooth.
This genus of Upper Cretaceous selachians was for a long time placed among the cestracionts, but recent discoveries of the nearly complete dentition render it more probable that its proper location is with the Myliobatidae. The living members of the family, the sea-devils, are broad, flat fishes, allied to the rays, with a disk-like body. Many attain an enormous size, fifteen or twenty feet in length, and weigh a thousand pounds or more. In some the pectoral fins take on almost the character of limbs, and are said to be used in scooping up their food and transferring it to the mouth. The teeth are flat and pavement-like, and are used for crushing crabs and shellfish. The fish are viviparous, and for the most part live in tropical or semitropical waters.
The teeth in Ptychodus are not less than 600 in number in each jaw, at least in some species. They are arranged in parallel rows, decreasing in size from within outward, except that in the supposedly upper jaws the median row is composed of small, low and smooth teeth, very much unlike the immediately adjacent ones. In P. mortoni there are eight rows on either side of this median row, or seventeen in all. The lateral teeth become more transversely elongated, the surface markings less conspicuous, and the form more unsymmetrical. About 15 species of the genus have so far been discovered, all from the Upper Cretaceous. One or two species, including our most common one, have been discovered in both Europe and North America, and it is not improbable that the identity of yet others will be established when they are better known. The teeth vary so much in size and shape in the same individual that the identification from single specimens is often impossible or a matter of great uncertainty.
Ptychodus mortoni. Plate XXV; plate XXVI, fig. 1; plate XXVII.
Ptychodus mortoni (Mantell) Morton, Journ. Acad. Nat. Sci. Phil., VIII, p. 215, pl. x, f. 7; Agassiz, Poiss. Foss., III, p. 158, pl. XXV, ff. 1-3; Leidy, Proc. Acad. Nat. Sci. Phil., (1868), p. 205; Ext. Vert. Fauna, p. 295, pl. XVIII, ff. 1-14; Cope, Cret. Vert., p. 294; Woodward, Quart. Journ. Geol. Soc., XLIII, p. 130; Cat. Foss. Fishes Brit. Mus., I, p. 159; Proc. Geol. Assoc., XIII, p. 191, pl. v, f. 4; Williston, Kans. Univ. Quart., ix, p. 30, pl. VII, VIII, f. 1, pl. IX--Alabama, Mississippi, Niobrara of Kansas, English Chalk.
Plate XXV--Ptychodus mortoni Mantell, natural size
Plate XXVI, Fig. 1--Ptychodus mortoni Mantell, part of dentition of upper jaw, as preserved in the matrix, four-sevenths natural size.
Plate XXVII, Fig. 1--Ptychodus mortoni, end of superior dentition, continuous with left end of fig. 1, plate XXVI, but less reduced. Fig. 2--Ptychodus mortoni, a transverse series of teeth, arranged more loosley, from near the right extremity of fig. 1, Plate XXVI, about two-thirds natural size; the upper series belong one at each end of the lower series.
This species is the most common one of this genus in the Kansas Cretaceous, occurring only in the Niobrara beds, so far as I am aware, and, for the most part at least, in the lower part of the beds. I have before me at the present time two excellent series of teeth of this species; one, including about eighty teeth, obtained from the estate of the late Joseph Savage; the other collected in the vicinity of Castle Rock, in Trego County, by Prof. G. E. Rose--an exceedingly interesting specimen, because most of the teeth are in place in the matrix. A number of the teeth of the Savage specimen have been arranged serially and photographed in plate XXV. Of course the arrangement is not the natural one, but the plate will show in an excellent way many of the characters of the teeth better than they can be described. In plates XXVI and XXVII are given three views of portions of the Rose specimen; that of plate XXVI (fig. 1) shows a little more than one-half of the upper view. One end (the left of the figure) has been folded underneath obliquely. This folded end is shown in plate XXVIII [sic., XXVII], fig. 1. Figure 2 of the same plate gives a view of a transverse series, as arranged from the loose teeth taken from the right end of the specimen--the one that protruded from the chalk when discovered. About 550 teeth, all told, have been obtained, and doubtless not a few had been lost before the specimen was discovered. The set is referred to the upper jaw, on the supposition of Woodward that the small median teeth belong in this jaw.
Not a trace of osseous substance is preserved in the specimen. The cartilage of the sharks' jaws is often preserved in a soft, calcified condition, but it is evident that the material in which the teeth of Ptychodus were lodged was of a more perishable nature, accounting doubtless for the fact that Ptychodus teeth are so rarely found associated.
The teeth of this species differ markedly from those of all other known species, in having the center of the crown raised into a conical apex, the summit of which is crossed by a short transverse ridge from which other diverging ridges run. In the smaller lateral teeth these ridges become less well marked and occupy a relatively smaller space, becoming almost obsolete in the fifth row. The marginal area is formed of fine reticulations in many of the larger teeth, though in most of these and in all the smaller teeth the markings are more like a fine punctuation, clearly visible only with the aid of a lens, giving a uniform, finely roughened appearance. The median upper row is composed of low, flattened teeth, transversely oval or sub-quadrate in shape, with a slight elevation in the middle, and finely roughened throughout the whole coronal surface, there being only the slightest trace of the divergent ridges on the summit of the elevation. This does not quite agree with Woodward's description of these teeth, in which he states that they are "not marked with the radiating ridges, but exhibit a minute smooth eminence in the middle of the crown." Possibly this effect is due to wear.
Ptychodus polygyrus. Plate XXIX, fig. 9; plate XXX, fig. 14.
Ptychodus polygyrus (Buckland) Agassiz, Poiss. Foss., III, p. 156, pl. XXV, ff. 4-11, pl. XXV-B, ff. 21-23; Gibbes, Journ. Acad. Nat. Sci. Phil., I, p. 299, pl. II, ff. 5, 6; Leidy, Proc. Acad. Nat. Sci. Phil. 1868, p. 208; Cope, Cret. Vert., p. 294; Woodward, Cat. Foss. Fishes Brit. Mus., I, p. 143, pl. V, f. 7--Senonian, Turonian of Europe, Rotten Limestone of Alabama, Niobrara of Kansas; Williston, cf. cit. 31.
? Ptychodus latissimus Agassiz, l.c., fig. 8; Dixon, Foss. Sussex, pl. XXX, ff. 1, 2.
Plate XXIX, Fig. 9--Ptychodus polygyrus Buckl., a little enlarged.
Plate XXX, Fig. 14--Ptychodus polygyrus, from the side, natural size (the same tooth figured on Plate XXIX, Fig. 9).
A single tooth of very large size from the lower beds of the Niobrara Cretaceous of the Smoky Hill River is referred to this species provisionally. Until numerous specimens are examined there can be no certainty of its correct location, though the resemblances are sufficiently great to render the determination not improbable; at least with some of its varieties.
Ptychodus martini. Plate XXVIII.
Ptychodus martini Williston, cf. cit. 32.
Plate XXVIII--Ptychodus martini Willist., three-fourths natural size; the teeth were discovered disassociated.
A large series of teeth, 110 in number, found together in the Niobrara chalk of the Smoky Hill River, and collected by Mr. H. T. Martin, cannot be identified with any described species. I have photographed them, arranged as symmetrically as possible, but with no assurance that the arrangement is a natural one. In fact, it is not improbable that the teeth belong to both upper and lower jaws. The teeth apparently from the lower median row are much elongate transversely, with a very flat crown, wherein they differ from the teeth of other known species. The ridges are nine or ten in number, and reach nearly to the lateral margin. In some of the teeth several of the ridges form loops near the extremities. The marginal area of granulations is small, and presents scarcely any distinct vermiculations. The teeth of the lateral rows are less elongated than those of the middle one, though still more so than is usual. The granulations become rather more extensive in area proportionally in the small teeth, as is the case with other species. A series (left vertical row of the plate) that may belong in the medio-lateral rows of the upper jaws are more nearly square in shape, and the crown has a distinct, though low, convexity extending over nearly its whole area. Antero-posteriorly the surface is nearly flat, with a moderate convexity of the margin. The surface posterior to the large grooves on the upper part shows small, radiating and branched ridges.
The largest teeth measure 45 by 20 mm; the ones more nearly square, 35 by 25 mm.
Ptychodus anonymus. Plate XXIX, figs. 5-8, 16-18, 20-22, 24.
Ptychodus anonymus Williston, cf. cit. 32.
Plate XXIX, Figs. 5-8--Ptychodus anonymus Willist., natural size.
Plate XXIX, Figs. 16-18, 20-22, 24--Ptychodus anonymus Willist., nearly natural size.
Seven teeth of nearly uniform size, four of them united in the matrix, from Walnut Creek, Kansas, seem to belong to a species distinct from any previously described (figs. 16-18). They are of about the same size as those described as P. whippleyi and P. occidentalis, but will be distinguished from the former by the more broadly conical crowns. In the teeth of this size of P. whippleyi the crown is much compressed, standing up, tooth in the present specimens they are nearly straight or gently concave from the apex to the rims. From P. occidentalis the species will be distinguished by the very distinctly reticulate marginal areas, the transverse ridges not reaching to the rims of the crown. Other specimens agreeing in these characters are from the Niobrara. The horizon is probably Benton.
Ptychodus occidentalis. Plate XXIX, fig. 4; plate XXX, fig. 13.
Ptychodus occidentalis Leidy, Proc. Acad. Nat. Sci. Phil. 1868, p. 207; Ext. Vert. Fauna West. Terr. p. 308, pl. XVII, ff. 7, 8, pl. XVIII, ff. 15-18: Cope, Cret. Vert., p. 244; Williston, cf. cit. 33--Niobrara, Benton of Kansas.
Plate XXIX, Fig. 4--Ptychodus occidentalis Leidy, natural size.
Plate XXX, Fig. 13--Ptychodus occidentalis, enlarged nearly two diameters.
Two teeth, one from the same conglomerate that yielded the teeth referred to P. janewayii, the other, without locality, from Mr. Joseph Savage's collection, I refer to this species. The species differs from the following in having the transverse ridges continued to the lateral rims, and not separated by an area of fine reticulation: The anterior surface has finer, elongated, nearly straight ridges and grooves in this species, while in the others the markings are reticulate or vermiculate.
Ptychodus janewayii. Plate XXX, figs. 9, 10, 11.
Sporetodus janewayii Cope, Hayden's Bull. U.S. Geol. Surv. No. 2, (1874), pl. XLVII.
Ptychodus janewayii Cope, Cret. Vert., p. 244; Williston, cf. cit. 33.
Plate XXX, Figs. 9, 10, 11--? Ptychodus janewayii Cope, enlarged.
"Surface irregularly convex, covered with a dense layer, which does not exhibit pores, and is thrown into transverse or oblique ridges. Surface with four folds, which traverse it obliquely from border to border. At the base of the outer, at one end, is a series of adherent tubercles; at the basis of that, at the opposite end, is a broken fold, with tubercles at its outer base. Length, 0.0045 m; width, 0.0025 m. A portion of a larger and more central tooth has the surface with an unsymmetrical convexity, and is crossed transversely by five folds, from border to border." [Cope, l. c.]
Three small teeth, shown enlarged in plate XXX, ff. 9-11, from the conglomerate containing specimens of Corax curvatus, appear to belong to this species. The horizon of the conglomerate is near the line of contact between the Dakota and Benton, in Ellsworth County. Cope's type was from a bed of conglomerate containing Lamna and Isurus teeth of small size near Stockton. It is probable that the horizon is the same in both.
Ptychodus whippleyi. Plate XXIX, figs. 10-15.
Ptychodus whippleyi Marcou, Geol. North Amer., p. 33, pl. IX, f. 4; Leidy, Ext. Vert. Fauna, p. 300, pl. XVIII, ff. 19, 20; J.S. Newberry, Rep. Expl. Exp., p. 147, pl. 111, f. 2: Cope, Cret. Vert., p. 294: Williston, of. cit. 34--Cretaceous, Texas (Marcou, Leidy); Kansas, Arkansas Valley (Cope); Colorado, New Mexico.
Ptychodus janewayii Cope, Cret. Vert., p. 244; Williston, cf. cit. 33.
Plate XXIX, Figs. 10-15--Ptychodus whippleyi Marcou, nearly natural size.
Thirteen teeth from Dallas, Texas, and a number of others received from Mr. Frank Springer, collected in the vicinity of Las Vegas, in New Mexico, agree with the descriptions and figures of this species, as given by Leidy. The same species has been referred to the Niobrara chalk of the Arkansas Valley by Cope. If his determination and locality are correct the species must be referred to the Benton of Kansas, since the Niobrara does not occur in the Arkansas Valley. A single specimen from the Benton of Kansas in the museum, without definite locality, seems to agree pretty well with the Texas specimens, but the specimen is an uncharacteristic one and may pertain to some other species.
Some of the teeth referred to this species show a marked resemblance to those figured by Woodward [3. Cat. Foss. Fishes Brit. Mus., I, pl. V, fig. 2.] (P. rugosus), and by Dixon (P. altior Dix.)
The European species is described as having the sides of the median elevation of the crown smooth, which is not the case with the present species, the grooves continuing midway into the lateral granulations.
Ptychodus, sp. Plate XXIX, figs. 2, 3; plate XXXI, fig. 53.
Ptychodus, sp., Williston, cf. cit. 34.
Ptychodus janewayii Cope, Cret. Vert., p. 244; Williston, cf. cit. 33.
Plate XXIX, Figs. 2, 3--Ptychodus, sp. indet.
Plate XXXI, Figs. 53--Ptychodus, sp., enlarged one fourth.
Four teeth of moderately large size, from the Benton Cretaceous, of Salt Creek, Russell County, and two others of smaller size, also from the Benton, seem to belong to a species distinct from any hitherto known. The larger ones will be distinguished from those referred to the upper series of P. martini, which are of nearly the same size and shape, by the smaller area of transverse ridges, and the much larger area of marginal reticulations, which are coarser. The teeth are more nearly square and the convexity of the crown is greater. The two teeth of smaller size probably belong with the others. It is possible that some of these teeth may belong with P. polygyrus.
The other described species of this genus are the following:
Ptychodus mammilaris Agassiz.--Senonian, Turonian, and Cenomanian, Europe.
Ptychodus rugosus Dixon.--Senonian, England.
Ptychodus decurrens Agassiz.--Senonian, Turonian, and Cenomanian, Europe.
Ptychodus multistriatus Woodward.--Senonian and Turonian, England.
Ptychodus latissimus Agassiz.--Turonian and Senonian, Europe.
Ptychodus papillosus Cope, Cret. Vert. 294.--Upper Cretaceous, Colorado.
Ptychodus triangularis Reuss.--Upper Cretaceous, Bohemia.
Ptychodus levis Woodward.--Lower Chalk of England.
Kansas Geological Survey, Volume V1, Cretaceous Fishes
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