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Gli squali fossili

Otodus

AGASSIZ, 1843
Extinct megatoothed mackerel shark
Lower Paleocene - Middle Eocene
Ordine Famiglia
Lamniformes BERG 1958 Otodontidae GLIKMAN 1964

The oversized teeth of this family hold a particular fascination for many. Those of Otodus are the earliest to reflect this odontological characteristic which culminates in the huge teeth of Carcharocles megalodon (AGASSIZ, 1837) during the Pliocene. As a member of this high profile family, there is rarely unanimous agreement on any group of statements that are assembled. (An excellent example is recent research by Gordon Hubbell presented at the 1999 AES meeting. After studying 95 associated C. megalodon teeth from Central Florida, he has begun to question whether this genus should even be considered a Lamniform.) With this potential for disagreement in mind, I will attempt to be as brief and unopinionated as possible.

This genus (and other family taxa) is known from isolated and/or associated teeth and vertebrae. The teeth are triangular in shape, bear (usually large) triangular and divergent lateral cusplets (occasionally more than one) and can be quite massive (reaching 10 cm per Kent, 1994). The dentition is cutting in design with upright anteriors -- the laterals (and posteriors) become more inclined distally. The crown's enameloid is smooth and the lingual face convex (growing stronger as teeth increase in size). There is a well-marked basal groove (broader medially), the bulky root has a prominent lingual protuberance and there are one or more scattered foramina. The cutting edge is smooth in teeth identified as Otodus obliquus AGASSIZ, 1843. Teeth of this design with irregularly serrate cutting edges are ascribed to O. subserratus (AGASSIZ, 1843).
 

Fig. 1 - Otodus obliquus anterior
70 x 32 mm 
Potapaco Mbr, Nanjemoy Frm, Virginia
From the collection of Mike Folmer

Otodus obliquus is a widespread species, reported from the Danian (Lower Paleocene) through Ypresian (Lower Eocene) sediments of Europe, Africa & North America. The serrated variation, Otodus subserratus, is scarcer, apparently appearing in the Middle Ypresian of Europe and North America.
 

Fig. 2 - Otodus subserratus lateral
35 x 35.5 mm 
Woodstock Mbr, Nanjemoy Frm, Maryland
From the collection of George Fonger

An alternate opinion views these megatoothed sharks as a single taxa, evolving through time. In this scenario, the currently recognized species are deemed morphospecies or chronospecies, wherein temporal snapshots (the fossil record) of various fauna suggest the presence of multiple species. Following this logic, the basal Cenozoic tooth morphology would be represented by Otodus appendiculata (AGASSIZ, 1843) (see: Cretolamna appendiculata) which transitions into O. obliquus during the Late Paleocene, and Carcharocles auriculatus (BLAINVILLE, 1818) [= O. subserratus] in the Middle Ypresian. The chronospecies arguments (unpublished) are very strong and may become more relevant in the future.
 

Fig. 3 - Otodus or Cretolamna appendiculata
25 x 21 mm 
Aquia Formation (Paleocene), Maryland

 
Fig. 4 - Otodus obliquus posterior
7.3 x 9.6 mm 
Potapaco Mbr, Nanjemoy Frm, Virginia

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