Fossil of the month: Saivodus sp.
How big was Sauivodus?
For some modern sharks there is a relationship betweeen the height or length of the largest tooth in the front of a shark’s jaw and the size of the shark (e.g., Applegate, 1965). Different relationships have been calculated for different types of sharks. Shimada (2004) found relationships between tooth sizes and body sizes for modern Sand tiger sharks. He determined different equations for three different positions of teeth in the upper jaw. If Saivodus, has similarly shaped teeth to modern sand tigers, perhaps it had a similar body size relationship as well (and that’s a big if!). This is called an ‘if-then’ statement in science. A complication is that it is difficult to tell if isolated fossil teeth were the largest teeth in an individual’s mouth or if the teeth collected were positioned in front of the mouth. Sharks commonly have decreasing sizes of teeth from the front to the back of their mouths. Also, the relationship determined by Shimada was based on a small sample size, a maximum tooth crown height of 25 mm, and a maximum body length of 275 cm. But if (a) Saivodus was proportionally similar to a modern Sand tiger shark, (b) the teeth in the KGS collection are proportional to the size of the original shark, (c) the isolated Saivodus teeth represent the largest teeth in the shark’s mouth, and (d) results can be extrapolated for larger teeth and body sizes then were sampled by Shimada (2004) in his equations, then using the equation for the largest tooth in the anterior of the mouth:
Specimen Crown height (CH) BL=−26.665 + 𝐶𝐻*(12.499) Calculated body length (BL)
Saivodus?, KGS 1002 36 mm à 4.2 m, 13.9 ft
S. striatus, KGS 1003 26 mm à 3.0 m, 9.8 ft
S. striatus, KGS 116097A 17 mm à 1.9 m, 6.1 ft
Three specimens with complete medial cusps for size estimations. KGS 1002 has a broken back (lingual, inner) side so we can’t tell if it had cusplets or ridges on the bottom of its basal platform, which would help to identify the species. The long narrow medial cusp, and rounded edge front edge of the platform indicates it is probably Saivodus.
Because specimen 116097a is smaller and has a medial cusp more inclined than the other teeth, it may be a lateral, and possibly a lateral-posterior tooth, rather than a tooth at the front of the mouth (anterior). Shimada’s equation for an anterior lateral tooth is BL=-25.189 + CH*(18.270). Using this equation, the calculated body length of the Saivodus shark for that tooth would be 2.85 m (9.4 ft). If the tooth, however, is a posterior lateral tooth, then the correct equation would be BL=44.069 + CH*(43.013). Using this equation, the calculated body length of the Saivodus shark would be 7.75 m (25.4 ft)! You can see that the first equation, based on an assumption of a tooth position at the front of the mouth, provides a minimum estimate of the shark’s length; but a wide range of estimates are possible.
In addition, six specimens in the KGS collection have broken medial cusps. If only the preserved height of those teeth are used in the first equation, then the minimum estimated body lengths would range from 2.8 to 11.8 ft. Duffin and Ginter (2006) noted that the base of Saivodus’ medial cusp was generally 0.3 times the height of the cusp. If the unbroken cusp height is proportionally estimated from this equation, then the estimated body lengths would be 8.9 to 13.3 ft. Hence, the teeth of Saivodus striatus sharks in our collection may have been from approximately 6 or 8 to 14 ft long. For comparison, this range would include the modern Sand tiger shark, as well as many better-known sharks such as Blue sharks, Bull sharks, Lemon sharks, and Mako sharks. The largest Saivodus teeth known are as much as 6 cm tall (Duffin and Ginter, 2006), which would equate to a shark nearly 24 ft long! Lengths above 20 ft, are closer to a modern Great White shark! These numbers are only estimates, but they provide a general idea of the possible range of sizes for extinct Saivodus sharks.
Text, photographs, and illustrations by Stephen Greb