Il sito italiano sugli squali

Gli squali fossili


Extinct sand tiger shark
Paleocene - Eocene
Ordine Famiglia
Lamniformi BERG 1958 Odontaspididae MÜLLER & HENLE 1839

The genus Striatolamia left a fossil record with teeth that can be easily confused with those from other genera. I find it particularly disconcerting to need to know the stratigraphic position before tendering an opinion as to whether an anterior tooth might be Scapanorhynchus or Striatolamia, or at other times, Carcharias or Striatolamia. The experts may find the subtleties "obvious", but I've never achieved that comfort level.

Striatolamia is represented by two named species in North America, S. striata (WINKLER 1874) from the Paleocene & early Eocene and S. macrota AGASSIZ 1843 from the Eocene. These two species have also been reported from Europe and North Africa.

The anterior teeth of this genus have an elongated crown, sigmoid in shape when viewed laterally, which bears striations on the lingual face. Lateral cusplets are greatly reduced or absent. Kent (1993) reports these teeth (from S. macrota) reaching 5.6 cm in height. The lateral teeth are lower and broader, the striations are weaker or lacking entirely and the cusplets reduced, often appearing as no more than a scalloped heel. Teeth from the Eocene species, S. macrota, are larger than their Paleocene counterpart and bear shorter striations. It is arguable whether there are actually two species or just an evolutionary trend toward larger teeth within a single species (the Eocene teeth termed S. striata actually being juvenile S. macrota).

Compared with the striated-crown Carcharias species, the Striatolamia crowns tend be more erect (less sigmoid) with stronger striations and more greatly reduced cusplets. In contrast to Striatolamia, the striations on Scapanorhynchus tend to be stronger and extend beyond the basal margin of the crown's enameloid.
Fig. 1 - Striatolamia striata - lateral
16.5 x 14.0 mm
Aquia Formation (Paleocene), Maryland

Fig. 2 - Striatolamia macrota - anterior
left 31.5 x 15.0 mm and right: 27.5 x 15.0 mm 
Nanjemoy Formation (Eocene), Virginia

Fig. 3 - Striatolamia macrota - laterals
from left to right 27 x 23, 16 x 16, 16 x 13 mm
Nanjemoy Formation (Eocene), Virginia

© 1999-2013 di Antonio Nonnis