THE SHARKS

Extinct Early Mako
Isurus praecursor (Leriche)
aka Macrorhizodus praecursor
 

Age - Eocene  Commonality - Uncommon

One of two species of mako shark found in New Jersey, Isurus praecursor is the earliest known mako and is restricted to the Eocene.  Both species, Isurus praecursor and Isurus desori belong to the narrow-toothed form of mako. Averaging between ½ to 1 ½ inches long, the teeth of I. praecursor, when compared to other teeth from Monmouth County are relatively robust and the anterior teeth have no cusplets. A nutrient grove is lacking, or a best shows as a weak depression. On specimens that are not too stream worn nutrient pores may be present, these may form what looks like a single opening due to clustering and/or stream wear. Kent mentions that the “lateral teeth of I. praecursor are nearly indistinguishable from those of the later Isurus species”.¹ Most reference material notes the similarity between these two species and suggests using stratigraphic origin as an aid to identification. Large sand tigers that are missing their cusplets may be mistaken for makos.
  

Anterior and lateral teeth of Isurus praecursor.
 

Different views of an anterior I. praecursor. This species has the shortest,
stoutest crown on the anterior teeth of all the Isurus species.

 

Lateral teeth if Isurus praecursor. The roots on the lateral
teeth are large with a "block like" appearance. Small cusplets may
 be present
 

"Weak" cusplets on a lateral tooth.
Author's Note: The few lateral teeth of I. praecursor that I have
collected all have cusplets. I currently attribute this to the limited number of
specimens collected of both Isurus species from NJ. 
 

Nutrient pore on an anterior tooth.

¹ Kent, W.B, 1994. Fossil Sharks of the Chesapeake Bay Region, Egan Rees & Boyd, Inc., 57pp.
 

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