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Gli squali fossili

Carcharias

RAFINESQUE 1810
Tigre di sabbia
Cretaceo inferiore - Recent
Ordine Famiglia
Lamniformes BERG 1958 Odontaspididae MULLER & HENLE 1839

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:
Striated species: C. holmdelensis, Campanian & Maastrichtian of NJ, DE & GA [Marshalltown, Mt Laurel & Severn]. C. whitei (ARAMBOURG, 1952), Paleocene (Ward & Wiest, 1990) [Brightseat Frm] C. teretidens WHITE, 1931, Late Paleocene - Eocene [Aquia Frm] C. acutissima, Oligocene - Pliocene [Piney Pt, Old Church Calvert, Choptank, St. Mary's, Eastover & Yorktown Frm] C. reticulata (PROBST, 1879), Miocene [Old Church & Calvert Frm].
Smooth-cusped species: C. samhammeri (CAPPETTA & CASE, 1975), Campanian - Maastrichtian of NJ, DE [Marshalltown, Mt. Laurel & Severn Frm] C. hopei, Late Paleocene - Eocene of AL, VA, MD & NC [Aquia, Nanjemoy & Piney Pt Frm] C. cuspidata, Oligocene - Miocene [Calvert, Choptank, St. Mary's & Eastover Frm] C. taurus, Pleistocene [Columbia Frm].


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.


Fig. 1 - C. hopei
Anterior 14.0 x 6.7 mm
Aquia Frm - Paleocene,
Maryland

Fig. 2 - 4 Carcharias hopei - Nanjemoy Frm - Eocene, VA
Fig. 2 (left) - Lwr Ant 3 -- 17.5 x 9.0 mm 
             (right) - RH Lwr Ant 2 -- 23.0 x 10.0 x 6.1 mm
Fig. 3 (left) - LH Upr Anterior 3 -- 20.0 x 18.2 x 4.8 mm 
(right) - RH Upr (?1st) Lateral -- 12.5 x 13.0 mm
Fig. 4 (side) - Lwr ?posterio?-lateral -- 13.5 x 9.5 mm 
       (top) - LH Upr postrio-lateral -- 9.5 x 9.5 mm 
(bottom) - Upr Lateral -- 7.0 x 7.0 mm 

Fig. 5 - Carcharias ??robustus
Note: may represent C. hopei
[Left] ?Lower anteror 22.0 x 15.5 mm
[Right] Upper anterior 19.4 x 10.0 mm
Potapaco Bed B, Nanjemoy Formation - Eocene, Virginia 

Fig. 6 - Carcharias teretidens
Upr (?3rd) anterior 15.0 x 11.0 mm
Lateral 13.8 x 13.2 mm
Nanjemoy Formation - Eocene, Virginia 

Fig. 7 - Carcharias cf koerti
Anterior 33.0 x 19.5 & Lateral 18.0 x 18.0 mm
Castle Hayne Frm - Eocene, North Carolina 

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