Pelagic Stingray Shed Teeth

Jim Bourdon, Scott Greenwald and Henry Mollet
Illustrated by Jim Bourdon, Copyright © 1997


From the outset, many objectives were clear, others emerged has the study progressed. They currently include:

Tooth Characteristics

There appear to be several morphological constants in these teeth - many are characteristic to the family, others are less common.

File Groups

When studying the dentition only, there appeared to be two general tooth-types, medial and lateral. In studying shed teeth however, there appears valid arguments for assigning three groups: anterior, lateral and posterior. Anterior teeth have elongated cusps, laterals appear cuspidate when viewed labially only, and posteriors have a high, level, laterally elongated and labio-lingually compressed transverse crest.

Specimen Numbering

At the time of this writing, these specimens have not been assigned to a particular collection and are being tracked only by collection date. The preliminary numbering system is YR-ORG-SP-MMDD-NN (i.e., 97-MBA-DV-0117-22) and has a shorthand notation of MMDD-NN.

An arbitrary "tooth-type" designation has not been developed. For discussion purposes, the nomenclature employed only refers to the illustration's number. This should be a temporary condition. Described tooth-types which are not illustrated are assigned a one-up numbering system with a "NYI" (not yet illustrated) prefix.

Collected Lots

This study began with a sample of 121 teeth that represented three weeks of shedding. Recovery techniques were subsequently refined leading to significantly higher yield. Samples are now collected weekly with the intention of studying the mid-month lot. The below discussion is based on the March 14th sample (97-MBA-DV-0314) which yielded 141 teeth -- pathological teeth excluded, the comparative basis is 136 teeth.

General Description

Male and female pelagic stingray teeth consist of a bilobate root and a cuspidate crown. The teeth are small, ranging in width (mesio-distal) from 2 to 4 mm and depth (labio-lingual) from 1 to 2-1/2 mm. A moderately deep and wide nutrient groove is present between the two, lingually directed, lobes. There is a single central pore which usually contains a single foramen. Lateral foramina, on the interior surface of the lobes, have not been observed. The root lobes do not extend beyond the lateral margins of the crown.

Anterior and lateral teeth of both sexes have cuspidate crowns, in contrast to the typical globular design associated with most stingrays. The medial teeth have strong, lingually directed cusps, which are similar to the "typical" high-cusped male stingray tooth -- such as those from Dasyatis americana HILDEBRAND & SCHROEDER, 1928, D. sayi (LESUER, 1817) and D. sabina (LESUER, 1824). Unlike the cited examples, the labial face does not have strong enameloid ridges or a medial depression running the length of the cusp. In lateral teeth, the cusp is weaker and more upright. In lieu of a cusp, the posterior teeth have a prominent, laterally elongated, transverse crest which adjoins a strong transverse depression on the labial face. On the lingual face, the transverse crest has longitudinal ridges. Medial and lateral teeth have a weak depression on the labial face which is located at the juncture of the crown base and the cusp.

The labial face of all teeth have a pitted appearance which results from the depressions created by numerous small meandering enameloid ridges. No teeth have a "cutting edge" as in many shark or skate teeth. Rather, the acute angle of the transverse edge of the cusp and transverse crest have a serrate edge created by the numerous enameloid ridges.

As a dasyatid, there is a unique feature represented in these teeth -- the development of a second cusp. An incipient reflection of this characteristic can be seen in many teeth, usually as a longitudinal depression in the lingual face of the crown. Eight percent of the teeth, originating in medial and lateral positions, have a second cusp. These bicusped teeth appear sporadically within the dentition, and are present in a file of teeth which are otherwise single-cusped. Unlike the mobulids, the other family developing additional cusps, this bicuspidate condition in the pelagic stingray is not associated with the mesio-distal elongation of the crown.

Sex and the isolated Pelagic stingray tooth

When studying the MBA shed tooth groups, certain information was available that would not be available when examining isolated teeth of unknown origin. Of primary importance was the relative sizes of male and female rays. The females were all larger, and examination by Greenwald & Mollet confirmed that the teeth were also significantly larger in size. A second factor was the availability of photographs of the dentitions themselves.

The anterior and most lateral teeth, as presented in this study, can be ascribed to a particular sex with a strong degree of certainty. To a lesser extent and with less confidence, the posterior teeth could be grouped by sex. This may not be the case when the origin of the teeth is unknown. If teeth from a large male were intermixed with those of a small female, it is unlikely that any posterior, and possibly lateral, teeth could be segregated. Anterior teeth from the first few files may show sexual dimorphism.

I make the final comment from experience with the previously described dentition. Based on size, and prior to extensive tooth study, that dentition was thought to be from a large male. The teeth from that dentition were compared with the small (male) teeth collected from the aquarium. Although smaller in size, these shed teeth all had counterparts in the dentition. When improved tooth collecting techniques were developed, a new group of small teeth were identified -- they were clearly anterior male teeth, but were not in the dentition. Once photographs of the MBA ray dentitions became available, they were compared with the shed teeth and the studied dentition. It became readily apparent that the dentition was from a small female rather than a large male. It was only the first few files that had teeth sufficiently different to ascribe that difference to anything other than size.

Additional research may yield subtle morphological details which will allow teeth of unknown origin to be confidently ascribed to a particular sex. However, at the time of this writing, relative size, a very poor basis for identification, is the only characteristic available for most isolated teeth.

High-Cusped Teeth (Anterior)

Several distinct types of strongly cusped teeth can be found in the sample. Because observations by MBA revealed that the female stingrays had much larger teeth than the males, it seemed relevant to separate tooth-types by size.

NOTE: All teeth were originally illustrated at 10X and have maintained
a similar enlargement factor (to one another) when digitized. From
left to right, the aspects are: lateral, lingual, labial, occlusal and basal.
In certain cases, a cuspal view has been added to the left or one or more
aspects may have been omitted.

Cuspal view
Specimen 54-C. hgt = 2.5, wid = 2.9, dep = 2.5 mm

Cuspal view
Specimen 54-B. hgt = 2.2, wid = 2.8. dep = 2.0 mm

Specimen 58-A hgt = 3.0, wid = 3.7, dep = 2.6 mm.

Specimen 58-B hgt = 2.8, wid = 4.0, dep = 2.6 mm.

Specimen 60-C hgt = 2.8, wid = 2.9, dep = 2.2 mm.

Specimen 58-D hgt = 2.6, wid = 2.3, dep = 1.9 mm.

Specimen 58-C. hgt = 2.0, wid = 2.6, dep = 1.6 mm

Low-Cusped Teeth (Lateral)

When viewed laterally, these teeth have a sharp apical surface, but there is no elongated cusp directed lingually. Viewed labially or cuspally, the crown has an angular (pointed) apex which provides a cusp-like appearance.

Specimen 54-D. hgt = 2.8, wid = 3.5, dep = 2.3 mm

Specimen 54-E. hgt = 2.0, wid = 2.8, dep = 2.1 mm

Specimen 55-B. hgt = 1.7, wid = 2.4, dep = 1.9 mm

Non-Cuspidate Teeth (Posterior)

These teeth when viewed laterally have a relatively sharp apical angle, but when viewed from a labial aspect, have little or no acute apical angle, but rather an elongated apical edge. Teeth thought to be from distal positions of the dental band were originally placed into two groups, 54-A and 55-D. This lumping was based on a morphological composite observable when viewed laterally: 54-A teeth had a weakly concave labial face and an obtuse cuspal angle which gave the lingual face a labial slope. 55-D teeth had a more strongly concave labial profile and a more acute cuspal angle -- the upper lingual face is more upright. Since that time, 54-A teeth were found to be less homogeneous in design than 55-D, and have been further refined.

In the studied dentition, the upper posterior teeth were of the broad 54-D design and the lower teeth were similar to the 55-D tooth. Because of the variations in sizes within each group, it is likely that male and female teeth are represented within these groups.

Specimen 54-A. hgt = 2.1, wid = 2.5, dep = 2.2 mm

Specimen 58-E hgt = 1.9, wid = 2.7, dep = 2.0 mm.

Specimen 55-D. hgt = 1.5, wid = 2.1, dep = 1.6 mm

Bi-cuspidate Teeth

An unexpected morphological condition in this study was the presence of a second cusp in the teeth of this species. In the preliminary sample from January, a single tooth was fully cuspidate (illustrated in 55-A) but many (10%) displayed varying traces of this condition (incipient secondary cusps, longitudinal depressions in the lingual face of the crown, etc.). In that January sample, this condition was reflected in: 2/54-A, 1/54-B, 3/54-C, 1/54-D, 3/54-E, and 3/55-B teeth.

Since that time, a dentition was obtained which also reflected this characteristic. Because this is no longer deemed a singular event (although both MBA rays and the studied dentition were collected from a similar area and may reflect a characteristic of a localized population) only teeth which have two cusps (and not the incipient condition) are now being counted. In the 0314 sample, 13 teeth had a second cusp (2/54-B, 4/54-D, 3/54-E, 58-B, 58-C?, NYI-08 & 60-B).

Looking at the distribution of bicusped teeth (using the allocation-to-tooth-group methodology employed for the March 14 sample) within the dentition, nearly 25% of the lateral teeth display this condition while only 6% of the anterior and 3% of the posterior teeth display this characteristic. This could turn out to be a characteristic of lateral teeth only,

Specimen 55-A. hgt = 2.1, wid = 3.2, dep = 2.0 mm

Pathological Teeth

Two examples were set aside in the first sampling as pathological teeth. One dual crowned tooth (55-C, illustrated below) was clearly so, and the other had an inordinately broadened crown and one disproportionately enlarged root lobe. The March sample produced four pathological teeth. Specimen 0314-139 had three crowns, 0314-140, a laterally compressed tooth, a single root lobe and 0314-138 was a bicusped tooth with pathological root lobes..

Specimen 55-C. hgt = 1.5, wid = 2.9, dep = 2.1 mm


This aquarium sample provides shed teeth in superb condition. Not only are they not subject to the depositional and weathering stress associated with fossil teeth, but the rays themselves live the "Life of Riley" which includes their soft diet of squid. Compared with the shed teeth in the described dentition, the MBA samples retain many more features of the cusp.

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Page revised July 31, 1997