Ray and Skate Fossils
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Figs. 1a, 1b. Myliobatis gigas Cope. | ||
| 1a) Oral surface of lower dental pavement, somewhat
worn, and showing line of longitudinal striae or fissures of the gano-dentine
radiating backwards and outwards. Charles County near the Patuxent River.
Type of the so-called " M. vicomicanus." Acad. Nat. Sci.,
Phila.
1b) Transverse view of the same specimen at its posterior end (across the bottom of Fig. la) |
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| Fig. 2a, 2b. Myliobatis pachyodon Cope. | |||
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2a) Oral surface of imperfect lower dental pavement, the anterior end shown uppermost. (Type specimen.) Charles County near the Patuxent River. Acad. Nat. Sci., Phila. 2b) Transverse view of the same specimen. |
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| Figs. 3. Myliobatus frangens n. sp. Cope. | |||
| 3) Oral surface of imperfect lower dental pavement, somewhat worn, and showing curved outline of the anterior depression due to wear. (Type specimen.) Charles County near the Patuxent River. Acad. Nat. Sci., Phila | |||
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Fig. 4. Myliobatis or Trygon (?) sp. |
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| 4) Portion of large caudal spine of an eagle or sting-ray. Charles County near the Patuxent River. Acad. Nat. Sci., Phila. | |||
| Fig. 5. Aëtobatis arcuatus Agassiz. | |||
| 5) Inferior aspect of fragmentary tooth. St. Mary's River. | |||
| Figs. 6a, 6b. Notidanus primigenius Agassiz. | |||
| 6a) Inner aspect of tooth, the root much worn
away. Plum Point.
6b) Outer aspect of the same specimen. |
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Family MYLIOBATIDAE Müller
and Henle.
Genus Myliobatis Cuvier.
The best account of the dentition of this genus,
with valuable suggestions for the determination of fossil teeth, is given by
A. S. Woodward.1 The development of young teeth
has also been studied by Jaekel, 2 and the dentition
of some hitherto misunderstood fossil forms correctly interpreted by him.
It is stated in the report on the Eocene of Maryland,
pp. 264 and 265, that the "anterior end" of the large dental pavement
of Myliobatis magister Leidy is shown uppermost in the figures, but as
these were inadvertently turned upside down, the statement should be amended
so as to read posterior end. In most cases the orientation of Myliobatid dental
plates can be readily determined. Traces of wear, due to the comminution of
food during life, occur always at the anterior end; the transverse sutures of
the median teeth are usually curved posteriorly along the lateral margins; and
the superficial striae or wrinkles (when the gano-dentine layer is unabraded)
always radiate outwards on passing from front to back. A longitudinal section
shows that the median teeth are not only closely appressed against one another
throughout their height, but they overlap in a tectiform manner, each tooth
sloping obliquely backward.
Two species of Myliobatis have been described
by Cope from the Eocene marls of New Jersey, which seem to have escaped general
notice. These are M. glottoides 3 and M.
rectidens.3 M. serratus
Leidy, founded on much abraded teeth from the same horizon and locality, is
renamed M. leidyi by O. P. Hay 4, the
former specific title being preoccupied.
Myliobatis gigas Cope, 1867, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 140.
Myliobatis vicomicanus Cope, 1867, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 140.
Myliobatis gigas Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. viii, p. 241,
pl. xxxiii, fig. 4.
Myliobatis vicomicanus Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. viii
p. 242, pl. xxxiii, fig. 5.
Description.— Dentition large but
comparatively thin, the smooth coronal contour nearly flat in the lower jaw
and but slightly arched from side to side in the upper. Longitudinal superficial
striae well-marked, regularly deflected outwards on passing posteriorly. Median
teeth in the adult about nine times broader than long, more arched at the sides
than in the middle; lateral teeth longer than broad. Transverse sutures of median
teeth slightly recurved posteriorly along the sides, and to a lesser extent
(in the lower dentition) also in the middle.
This species is remarkable for the great tenuity
of the tesselated pavement in proportion to its size just as M. pachyodon
is remarkable for its excessive thickness. These differences are best understood
by a comparison of the cross-sections given on Plate XXVIII,
Fig. 3b, and Plate XXIX, Fig. 1b, of this volume, with Plate
XIII, Fig. la, of the Eocene volume. The lower dental pavement is relatively
narrower than the upper, and its median teeth are shorter. In the type-specimen
of the so-called "M. vicomicanus," shown in Plate
XXIX, Fig. 1, the median teeth are fully nine times as broad as they are
long. Cope's types of this species have already been figured by Leidy, although
for some unexplained reason certain fragments belonging to the left-hand side
of the upper dentition in front were omitted by the artist.
The transverse sutures, especially those of the
lower dental pavement and the longitudinal superficial striae, are curved similarly
to those of M. magister from the Eocene Phosphate Beds of South Carolina;
but the median teeth are shorter, flatter and much thinner than in the Eocene
species. The lower dental pavement exhibits a shallow longitudinal depression
along the median line, in which the transverse sutures are gently curved posteriorly.
In this respect the lower dentition resembles that of M. magister Leidy,
M. dixoni Agassiz, and some other species, while it is exactly opposite
to the condition presented in the upper dentition of M. fastigiatus Leidy.
The total length of the series of eleven median
teeth in the lower dental pavement shown in Plate XXIX, Fig.
1, (type of M. vicomicanus) is 8 cm. and the width of the largest tooth
6 cm. The extreme length of the upper dental pavement measured in a straight
line antero- posteriorly is rather more than 10 cm. or along the arc of its
curved surface 12 cm. Its largest median tooth has a width of 8 cm. and a length
of 1.1 cm.
Occurrence. — Calvert formation. Charles
County near the Patuxent river.
Collection. — Philadelphia Academy
of Natural Sciences.
Myliobatis pachyodon Cope, 1867, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 140.
Myliobatis pachyodon Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. viii,
p. 242, pl. xxxii. fig. 6.
Description. — Dentition large and
massive, the median teeth being unusually thick in proportion to their size.
Except as regards thickness, the median teeth are shaped similarly to those
of M. gigas Cope and the transverse sutures are similarly curved. The
species is intermediate in character between the accompanying M. gigas
and M. magister from the Eocene, the latter having longer median teeth
and more strongly curved transverse sutures. The type of the present species,
which appears to be unique, exhibits only the left half of four anterior median
teeth and portions of three elongate lateral teeth. The median teeth have a
length of 1.1 cm. and thickness of 2.1 cm. If, as indicated by the cross-section
and longitudinal striae, the pavement is preserved for rather more than one-half
its width, the median teeth must have been at least 6 cm. wide.
Occurrence. — Calvert formation. Charles
County near the Patuxent river.
Collection. — Philadelphia Academy
of Natural Sciences.
Myliobatis sp. Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. viii, p. 243,
pl. xxxii, figs. 7, 7a.
Description.— Lower dental pavement
nearly flat and relatively very thin, in cross-section resembling M. gigas
Cope. Median teeth about nine times broader than long, and with nearly straight
transverse sutures.
The specimen upon which the above diagnosis is
based was recognized by Leidy as belonging probably to a distinct species, its
most obvious characteristic being the nearly straight course of the transverse
sutures. The latter are not curved posteriorly at the sides nor in the middle,
as in M. gigas, nor is there a median longitudinal depression, as in
that and various other species. The median teeth are also relatively longer
than in the lower dentition of M. gigas, but the cross-section is much
the same in both.
In the specimen under consideration, which appears
to be unique, the superficial layer of gano-dentine has been entirely removed,
so that the triturating surface presents a punctate appearance where the numerous
nutrient tubules are exposed. Indications of wear are very conspicuous on the
three anterior teeth, as shown in the figure. Owing to the great amount of attrition
which the median teeth have undergone, their thickness is nowhere more than
1 cm. The width of the second median tooth counting from the front may be safely
estimated at 5 cm., and its length 0.9 cm. No significance is to be attached
to the slight irregularities in the course of two of the transverse sutures.
Occurrence.— Calvert formation. Charles
County near the Patuxent river.
Collection.—Philadelphia Academy of
Natural Sciences.
Aëtobatis arcuatis Agassiz, 1843, Poiss. Foss., vol. iii, p. 327.
Aëtobatis arcuatis Eastman, 1901, Md. Geol. Survey, Eocene, p. 102, pl. xiii,
figs. 8a, 3b, 8.
Aëtobatis arcuatis Hay, 1902, Bull. 179, U.S. Geol. Survey, p. 321.
This species is tolerably abundant in various
Miocene localities of Maryland, Virginia, North Carolina and New Jersey, but
the teeth invariably occur singly in the detached condition, and are more or
less water-worn or otherwise abraded. An examination of the type-specimens of
Cope's A. profundus, described from the Miocene of Charles County, corroborates
Leidy's opinion that these are only the worn anterior teeth of the species under
consideration.
Occurrence.— St. Mary's formation.
St. Mary's River. Calvert formation.
Charles County
near the Patuxent river.
Collections.— Philadelphia Academy
of Natural Sciences, Maryland
Geological
Survey, Museum of Comparative Zoology.
Suborder ASTEROSPONDYLI
Haase.
Family NOTIDANIDAE Bonaparte.
Genus Notidanus Müller and Henle.
Remains of this genus are uncommon in. the American Tertiary formations. A single specimen assigned to N. primigenius is recorded by Gibbes from the Eocene (?) of Richmond, Virginia, and the same form is mentioned by Cope as occurring in the Miocene of New Jersey, Maryland and North Carolina. According to A. S. Woodward, the stout, awl-shaped teeth from the "marls of New Jersey," described by Leidy 5 under the name of Xiphidolamia ensis, are referable to the symphysis of the upper jaw of Notidanus. The same author also remarks the evolution of the multicuspidate teeth in this genus is analogous to that observed in the grinders of the elephant, there being in both cases a multiplication of similar parts when they occur in series 6.
Notidanus primigenius Agassiz.
Notidanus primigenius Agassiz, 1843, Poiss. Foss., vol. iii, p. 218, pl. xxvii, figs.
6-8, 13-17 (? figs. 4, 5).
Notidanus primigenius Gibbes, 1849, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. i,
p. 195, pl. xxv, fig. 95.
Notidanus primigenius Wyman, 1850, Amer. Jour. Sci., ser. ii, vol. x, p. 234.
Notidanus plectrodon Cope, 1867, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 141.
Notidanus primigenius Woodward, 1886, Geol. Mag. [3], vol. iii, pp. 205, 258, 525.
Heptranchias primigenius Hay, 1902, Bull. 179, U. S. Geol. Survey, p. 300.
Description.— Principal cone of lower
lateral teeth relatively large, with prominent anterior serrations on its basal
half diminishing in size downwards; secondary cones usually six in number, all
acutely pointed, and attached to a deep, laterally compressed root, beveled
on its outer face. Principal teeth of the upper jaw less laterally elongated
and with fewer cusps than those of the lower jaw. Lower median tooth with a
well defined cusp.
The teeth of this species are intermediate in
character between those of N. serratissimus, which are usually smaller,
and N. gigas, which are longer and have a larger number of secondary
cones. The average length attained hy the lateral teeth is about 3 cm. Cope
states of his so-called N. plectrodon that "it presents fewer denticles
than any other species, and thus approaches distantly the N. recurvus
of Agassiz." Comparisons show, however, that both of these species are
founded on teeth referable to the upper jaw of N. primigenius. About
a score of specimens have been obtained in all from the Miocene of Charles County,
Plum Point and Fairhaven. The root is unfortunately injured in the specimen
shown in Plate XXIX, Fig. 6.
Occurrence.— Calvert formation. Charles
County near the Patuxent
river, Plum Point, Fairhaven.
Collections.— Maryland Geological
Survey, Johns Hopkins University,
Philadelphia Academy of Natural Sciences, Museum of Comparative Zoology.
1 Ann. Mag. Nat. Hist. [6], vol.
i, (1888) pp. 36-47; Proc. Geol. Assoc., vol. xvi, (1899), p. 3.
2 Die eocänen Selachier vom Monte Bolca, pp.
129-131, and 150-159. Berlin, 1894.
3 Proc. Amer. Philos. Soc., vol. xi, 1870, pp. 293,
294.
4 Amer. Nat., vol. xxxiv, 1899, p. 785.
5 Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. viii
(1877), p. 252, pl. xxxiv., figs. 25-80.
6 Nat. Sci., vol. i (1892), p. 674.
updated 3/2/05
(these web pages were prepared by R. D. Conkwright)