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Gli squali fossili


Tiger shark
Lower Eocene - Recent
Ordine Famiglia
Carcharhiniformes COMPAGNO 1973 Carcharhinidae JORDAN & EVERMANN 1896

Have Mouth, Will Eat. -- The Tiger shark is a circumglobal predator-scavenger. Favoring tropical and warm-temperate seas, this common coastal-pelagic species may be found in near-shore (estuaries & lagoons) and off-shore (to 140 M) waters of the continental & insular shelf. It is a large (usually less then 5, but reported to 7.4 M), active species and a strong swimmer. Probably the least specialized feeder amongst the sharks, Compagno (1984) reported its diet to include: bony fish (from eels to tarpon), sharks & batoids, marine reptiles (turtles & sea snakes), sea birds, marine mammals, invertebrates (cephalopods, crustaceans, gastropods & jellyfish), carrion and various otherwise inedible objects (human & natural trash).

The teeth of this dentition (gradient monognathic heterodonty) are reminiscent of a can-opener. They incorporate a triangular, distally directed cusp and a prominent distal heel. The heel usually bears cusplets and it (and the cusp's cutting-edge) is serrate (stronger basally). The crown's lingual face is convex, and the relatively flat labial face, overhangs the root. There is a well marked lingual protuberance and weak groove. The roots of medial teeth are much thicker than their lateral counterparts.

Tiger sharks have a fossil record dating to the Early Eocene. Cappetta (1987) included several species: Galeocerdo aduncas AGASSIZ 1843 known form the Lower Oligocene - Miocene of Europe, Miocene of Africa, North & South America and India, and from the Miocene and Pliocene of Japan; G. contortus GIBBES 1849 from the Miocene of the US (not Europe); G. cuvier (PERON & LESUEUR 1822), the extant species from the Pliocene of Europe, Africa and North America; G. eaglesomi WHITE 1955 from the Middle Eocene Africa & the Arabian Peninsula; G. latidens (AGASSIZ 1843) in the Eocene of Africa, Europe & North America; and G. mayumbensis DARTEVELLE & CASIER 1943 Miocene of Cabinda (western Africa), he noted its similarity to the teeth of G. eaglesomi.

The Eocene species, Galeocerdo latidens is found throughout the Atlantic Coastal Plain. In the Nanjemoy, it has not been reported from Potapaco sediments, but Ward & Weist (1990) included the species in the Woodstock Member (Early Eocene) and Piney Point Formation (Middle Eocene) of Maryland and Virginia. These teeth are regularly collected in the Castle Hayne of No. Carolina, and Eocene exposures of So. Carolina. The Physogaleus-like teeth of G. contortus are not only abundant in Mid-Atlantic Miocene sediments, such as the Pungo River, but are also found in the Oligocene sediments of the Chandler Bridge Form. of So. Carolina. (Although rarely reported from the No. American Pacific coast, G. contortus teeth have been recovered from the southern California area. The teeth of Galeocerdo aduncas are abundant in the Pungo River and there is on-going speculation as to whether or not the teeth of G. contortus may be a sexual or other variation of the aduncas tooth. The presence of G. aduncas in the Miocene faunas of Japan (Yabumoto & Uyeno 1994) and Australia (Kemp 1991) without specimens of G. contortus suggests that the two species are quite distinct. 

Galeocerdo latidens
Fig.1 (top): Piney Pt Frm, VA
(Middle Eocene) - 15.0 x 21.0 mm 
Fig.2 (bot): Woodstock Mbr, Nanjemoy Frm, MD
(Early Eocene) - 11.5 x 18.5 mm 
From the collection of Bob Weist

Fig. 3 (top) Galeocerdo aduncas
14.0 x 16.4 x 4.8 mm
Fig. 4 (bottom) Galeocerdo contortus
15.0 x 16.8 x 5.5 mm
Pungo River Form. (Miocene), NC

Fig. 5
Galeocerdo cuvier
20.0 x 21.5 mm
Yorktown Form.
(Pliocene), NC

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