The extant mackerels have a circumglobal distribution in higher latitudes of both hemispheres (boreal/cool temperate). They are medium-sized (to 3.5m) inshore to epipelagic sharks that largely feed on fish (teleosts and smaller sharks). Compagno (1984) limited the Salmon shark (Lamna ditropis HUBBS & FOLLETT, 1947) to the North Pacific and the Porbeagle (L. nasus (BONNATERRE, 1788)) to the North Atlantic and southerm hemisphere. Recent mackerel have a cutting-clutching dentition of rather homogeneous teeth, even between those of the anterior and lateral hollows (see slide-show).
The Lamna dentition reflects moderate monognathic & gradational heterodonty. The upper and lower anterior hollows include three tooth-positions; the upper third is reduced and the lower, medially recurved. Except for the first and third anterior positions, the cusps are distally inclined; the lowers are more erect, robust and lingually directed. The cutting-edge is smooth and extends to a small lateral cusplet on each shoulder. The smooth crown strongly overhangs the labial face of the root, a diagnostic key. The root is thick with well-developed lobes and a central foramen. When carefully scrutinized, most anterior and medio-laterals can be readily distinguished from other taxa.
The Fossil Record
There is no published fossil record of Lamna in North America. Le Hon (1871: 11) erected Otodus (=Lamna) rupeliensis, which according to Cappetta (1987:97) has been reported from the Oligocene of Belgium & Germany; this tooth-design has subsequently been moved to Isurolamna. Herman (1974) reported teeth similar to L. nasus from the Pliocene of Belgium; as can be seen in the accompanying images, the range includes Spain, the western North Atlantic and eastern South Pacific.
Although the accompanying Lee Creek specimen appears unique, it is probably present in numerous collections as a generic sand tiger or TBD (to be determined). I would be very interested in seeing/documenting other examples from the Lee Creek fauna.
Cappetta, H., 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Handbook of Paleoichthyology, 3B. Gustav Fischer Verlag, Stuttgart and New York, 193 pp.
Compagno, J., 1984. FAO Species Catalogue, Vol 4, parts 1 & 2 Sharks of the World. United Nations Development Program.
Herman, J., 1974. Quelques restes de Sélaciens récoltés dans les sables du Kattendijk à Kallo. I. Selachii - Euselachii. Bull. Soc. Belge Géol., 83, (1), pp 15-31.
Le Hon, H., 1871. Préliminaires d'un mémoir sur les poissons tertiaries de belgique. Brussels, pp. 1-15.