Gli squali fossili
Extant sandtigers are large (reaching 3.5 m), usually bottom dwelling sharks of continental and insular shelves in temperate and tropical seas. Sandtigers, alone or in groups, feed on bony fishes, other sharks & rays, squid and crustaceans. The grasping-cutting dentition is characterized by 2 or 3 awl-like anterior teeth, one or more smaller intermediates (upper), a series of shorter & broader laterals and numerous small posterior teeth. According to Compagno (1984), the common living species is the Largetooth sand tiger, C. taurus (RAFINESQUE, 1810). It has a scattered distribution, reported from temperate - tropical waters of the Atlantic and Indo-West Pacific shelf from the surf to 191 m. The Indian sand tiger, C. tricuspidatus (DAY, 1878) (?syn C. taurus) is a poorly known inshore & offshore (to 1600 m) species from the Indian Ocean (possibly extending into Western Pacific). Over the years, these species have bounced between various genera (Eugomphodus GILL, 1861, Synodontaspis WHITE, 1931 & Carcharias), leading to some confusion.
The dentition of Carcharias taurus has been extensively studied and is well known. The anterior teeth have long and slender cusps (sigmoid in profile) with lateral cusplets. The lingual face is strongly convex and bears irregular folds. The labial face is flat and smooth and the cutting edge is incomplete. The root is high with well-separated lobes, a prominent lingual protuberance and sharp nutrient groove. The lateral teeth are shorter, broader (particularly at the base) and flatter (more blade-like), and bear a cutting-edge which reaches the lateral cusplets (one or two pair). The strong folds or wrinkles seen in anterior teeth weaken significantly or disappear. The root lobes are more widely separated and the root-face flatter. Well over a dozen posterior files are present (per side). These teeth are short and relatively thick and gradate distally from a low cusp with lateral cusplets to a non-cuspidate design.
Fossil teeth, often from isolated positions, have formed the basis for new species. Species noted by Cappetta (1987) include: Carcharias acutissima (AGASSIZ, 1844), Oligocene - Pliocene of Europe; C. cuspidata (AGASSIZ, 1843), Oligocene - Miocene of Europe & No. America; C. holmdelensis (CAPPETTA & CASE 1975) Upper Cretaceous [Campanian] of New Jersey; C. hopei (AGASSIZ 1843), Lwr Eocene [Ypresian] of England & Morocco; C. koerti (STROMER 1910), Mid Eocene [Lutetian] of Africa; C. striatula (DALINKEVICIUS, 1935, Lwr Cretaceous [Albian] of Russia & France; C. substriata (STROMER, 1910), Paleocene - Lwr Eocene [Thanetian - Ypresian] of Africa and C. vincenti (WINKLER, 1874), Eocene of Morocco & Europe.
Welton & Farish (1993) included in their Texas fauna: C. amonensis (CAPPETTA & CASE 1975), Late Albian - Cenomanian, C. tenuiplicatus (CAPPETTA & CASE 1975), Cenomanian, and two undescribed species.
Kent (1994) included a well
researched list of Mid-Atlantic sandtigers which he found represented in
the Chesapeake Region (formations noted in brackets). He categorized them
by the presence or absence of lingual striations:
It's uncertain how many persons are expert with Paleogene sandtigers, and the author acknowledges that he's not one. The identifications of the below teeth from the Nanjemoy of Virginia reflect input from David Ward and Steve Cunningham.
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