ELASMO.COM - - David Ward on Sharks

Some Nanjemoy Nurse Sharks

Editor's note. As often as possible, outside sources are requested to verify identifications represented on this website. After encountering a number of conflicting identifications (in various publications) for certain Ypresian nurse shark teeth of the Atlantic Coastal Plain, David Ward was asked to lend his expertise to this project. The results were so unexpected, that it seemed appropriate to make his comments available to those interested in this topic. The attached & referenced images and text have been added for easier reading.
David wanted me to remind the reader that, "these opinions are just that - opinions. Alternative views (supported by reasoned argument) are not just welcome, but are essential to promote healthy debate which will eventually lead to a consensus and maybe the 'truth'."

Subject: Re: Question 3
Date: Mon, 25 Oct 1999
From: David Ward
To: Jim Bourdon

The species Ginglymostoma serra has been erroneously used for Palaeogene species of Nebrius by several authors (White, 1926:11, fig 5 - 13-17; White 1935:22, Dartevelle & Casier, 1943: 107; Arambourg, 1952: 143, and Cappetta, 1987: 80). Acrodobatis serra was described by Leidy (1877) from the Miocene Ashley phosphate beds of South Carolina. He figured four teeth; the least worn of which show a prominent principal cusp in labial relief over the whole of the labial crown. This is a characteristic of the teeth Ginglymostoma, rather than of Nebrius.

"The crown of these teeth is usually wider than high, and the base is extended downward at the middle in a rounded prominence, and backward posteriorly in a similar prominence. The summit rises in a tapering point, and the lateral acute borders exhibit seven or eight denticles successively decreasing towards the base. The teeth of figure 10, 11 have the main point worn off and the lateral denticles more or less abraded. The tooth of figure 12 has the main point partially worn off, and even that of fig. 13 has the extreme point somewhat blunted by abrasion.
The root of these teeth is a shallow basis with a trilateral outline, the angles rounded and the lateral ones slightly projecting."

Acrodobatis serra
from the Ashley phosphate beds
as described by Leidy (1877)

G. serra is NOT an Eocene species. Thus the tooth you figure as Ginglymostoma serra (left) would be better termed G. sp undescribed.

"Ginglymostoma" obliquus (Leidy, 1877) (i.e. Nebrius obliquus) is the senior synonym of the Early Eocene species also known as N. blankenhorni. N. thielense is a Middle Eocene species.

"Figure 14... represents a tooth nearly like those just described, but having the main point directed to one side... The specimen was obtained from the marl of Monmouth Co., New Jersey... The inner acute border of the crown is the longer, and is convex in its course from the base of the main point. It presents seven denticles succeeded by four minute ones. The construction of the base of the crown is like that of the preceding teeth."

Acrodobatis obliquus as described by Leidy (1877)

Thus you can call the Muddy Creek Nebrius - N. obliquus - a good All-American name.

The tooth pic you sent me (above) could be a juvenile N. obliquus - but I am unhappy about the size of the principal cusp. I would tend towards Ginglymostoma maroccanum (or G. maghrebianum)

I think G. maroccanum is the same as (i.e. jun. syn. of) G. maghrebianum - but I would not bet my life on it. I do not think the tooth (left) is G. subafricanum, but I'd go with G. maroccanum.

References
ARAMBOURG, C. 1952 Les Vertebres Fossiles des Gisements de Phosphates (Maroc-Algerie-Tunesie). Notes et Mémoires. Service des Mines et de la Carte Géologique du Maroc, 92: 1-372, 44 pls. Paris.
CAPPETTA, H. 1987 Chondrichthyes II, Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology Vol 3B, 193pp, 148 figs, Stuttgart.
DARTEVELLE, E. & CASIER, E. 1943 Les Poissons fossiles du Bas-Congo et des regions voisines (premiere partie). Annales du Museé du Congo belge, A. Ser.3, 2(1):1-200, pls.1-16, figs.1-60. Tervuren
LEIDY, J. 1877 Description of Vertebrate Remains, chiefly from the Phosphate Beds of South California. Journal of the Academy of Natural Sciences of Philadelphia, 2nd Ser. 8:209-261, 30-34. Philadelphia.
WHITE, E.I. 1926 Eocene Fishes from Nigeria. Bulletin. Geological Survey of Nigeria, No.10:7-87, pls.1-18, tbls.1-3, text-figs.1-25. London.
WHITE, E.I. 1934(5) Fossil Fishes of Sokoto Province. Bulletin. Geological Survey of Nigeria, 14:7-78, pls.1-10, text-figs.1-15. London.