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Gli squali fossili

Cetorhinus

BLAINVILLE 1816
Basking Shark
Eocene - Recent
Ordine Famiglia
Lamniformes BERG 1958 Cetorhinidae Gill 1862

As I write this page, the basking shark has made the news as an estimate 500 individuals have gathered off the Cornish coast. The news media talks about fisherman fleeing the local waters -- must be an amazing sight.
C. maximus (GUNNERUS, 1765), Extant Basking Shark
This huge shark, (to 10 with reports to 15 meters) is second only to the whale shark in size. It is characterized by its large mouth with numerous (200 files per jaw) small, similarly-shaped, hook-like teeth and extremely enlarged gill openings which incorporate unique gill-rakers. These plankton capturing devices are hair-like (mucous) denticles which are periodically shed and when found, help confirm the presence of this genus in the fossil record. C. maximus is a migratory species of temperate & boreal, coastal & off-shore waters.

Fossil Basking Sharks
According to Cappetta (1987), a single extinct (Oligocene-Miocene) species has been described, C. parvus LERICHE 1908, and that specimens from the Pliocene and later are attributed to C. maximus. He describes the teeth of C. parvus as being unlike those of the extant species and more reminiscent of Alopias exigua (PROBST 1879) with branching roots.

Below are illustrations of a Cetorhinus tooth and gill-raker. The tooth is from Sharktooth Hill (Kern County, California) and conforms well to Cappetta's illustration and description of a C. maximus tooth. The roots are robust but worn, weakly revealling the presence of two lobes. Cappetta suggests that the nutrient groove is narrow and significantly deeper in unworn teeth. A cutting edge is present, does not extend to the apex of the crown and is irregular near the root where the cusp appears "pinched". 
 

Fig. 1 - Cetorhinus cf maximus
Sharktooth Hill specimen, 7.0 mm in height
from the collection of Steve Alter

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