The Spurdogs are a highly successful genus of sharks that have a worldwide distribution. According to Compagno et al (2005) the genus is made up of 10 described and possibly another six undescribed species. The genus generally inhabits continental and insular shelves and slopes. Often traveling in large groups, the Spurdogs are bottom dwellers that feed mostly on bony fishes.

Although two species (Squalus acanthias LINNAEUS, 1758 & S. mitsukurii JORDAN & SNYDER, 1903) can be found circumglobally, others have strangely disjunct ranges. Squalus cubensis HOWELL-RIVERO, 1936 for example, ranges from North Carolina through the Gulf of Mexico and from southern Brazil through Argentina. S. megalops (MACLEAY, 1881) is known from south and western Africa, the China Sea and southern Australia. S. blainvillei (RISSO, 1826), if a valid species, can be found in the Mediterranean, eastern South Atlantic and Japan.

From a paleontological perspective, this suggests two things to keep in mind. First, there is little reason to consider location (other than water temperature & depth) as might be the case with a genus such as Squatina. Secondly, various Squalus species appear to be very stable over time. There would appear to be no valid reason (if there ever is) to use time as a relevant factor when determining a tooth's identification. For example, Squalus teeth from the Middle Atlantic's Oligocene, Miocene and Pliocene which compare well with S. acanthias are more likely to be from that species than some paleontological species erected on an ad hoc basis.

Squalus acanthias — The Piked dogfish

The most widely distributed species, S. acanthias inhabits boreal to warm temperate waters of both hemispheres. It can be found inshore or offshore from intertidal to 900 M. This slender-bodied shark may reach 1.5 meters and has been described as a powerful and voracious predator that preys largely on bony fishes, but also feeds on cephalopods, arthropods and other marine animals.

The distally directed cusps and tightly interlocked teeth create a long, serrate, knife-like edge in each jaw quadrant which may have from 20 to 30 teeth. Considering the strength of the jaws and feeding habits, Compagno (1984) referred to the dentition as being of a clipping design. The dentition has weak monognathic heterodonty. The angle of the cusp is slightly different between jaws, the crowns grow lower distally and upper teeth are more mesio-distally compressed than the lowers. Despite their small size, the Squalus tooth is quite robust. Viewed laterally, the base of the crown may be 60% as wide as the crown is high and the root is relatively massive. The crown is made-up of a blade-like cusp and a high distal heel. A smooth cutting-edge extends the length of the crown. Compagno (1984) notes that the cutting edge in all extant species is smooth. The base of the labial face bears a long strong apron.

The Fossil Record

Cappetta (1987) notes that this genus has been reported from the Upper Cretaceous of Belgium, Lower Eocene of the USSR, Oligocene of Oregon & Czechoslovakia and Miocene of Japan. He went on to list five fossil species.