Cappetta (1992) erected this genus for fossil teeth formerly ascribed to Galeorhinus.
Lacking skeletal remains or associated tooth sets, he compared the teeth ascribed
to G. lefevrei (DAIMERIES, 1891) with those of other extant triakid genera, finding only
those of Galeorhinus and Hypogaleus to have a significant resemblance. The contrasting
features that precipitated the new genus included the cusp thickness, cusplet number and
shape and a marked bourlette. North Americans seem to have been slower to adopt
this reassignment than their European counterparts.
In modern oceans, Trikidae is a rather large family of small to moderate-sized active
sharks. According to Compagno (1982), they inhabit warm & temperate coastal seas
(continental and insular) from shore to outer shelf (Iago is a deeper water genus
having been reported to 2000 meters). They are bottom or mid-water feeders of
invertebrates and fishes.
Compagno (1999) includes in the family Triakidae, 38 species in nine genera, most
(22 species) in Mustelus. With the exception of the circumglobal genus Galeorhinus,
the 6 genera Cappetta compared (Hemitriakis, Furgaleus, Iago, Gogolia,
Galeorhinus and Hypogaleus) are relegated to the waters (often quite regionalized)
of the Western Pacific and Indian Oceans. If present distribution was introduced as a
criteria, Cappetta's comparison would be limited to a single species, G. galeus
(LINNAEUS, 1758), the only extant member of the genus.
To the author's knowledge, recovered teeth of lefevrei reflect monognathic heterodonty
similar to G. galeus, and only odontological variations (well within the boundaries
established for extant taxa) of tooth morphology can be employed to differentiate the
teeth of G. galeus from those of lefevrei.
Teeth now ascribed to Pachygaleus lefevrei have been found in Lower and Middle
Eocene deposits of the Anglo-French-Belgium Basin, but interestingly enough,
they have not been reported from contemporary sediments of North Africa. In the
Western Atlantic, these teeth have been found in the Palaeocene (Aquia Formation)
and Eocene (Nanjemoy) of Chesapeake Bay region.
Similar to those of Galeorhinus, these teeth are characterized by a crown with a
distally directed main cusp & multiple cusplets on it's distal margin and a root
which is relatively thin & has a nutrient groove which expands labially.
Most distinctive, however, is the bulging base of the labial face of the crown
which overhangs the root. Distinguishing Pachygaleus teeth from Galeorhinus
are an increased number of cusplets on a distal heel which joins the main cusp
at a relatively higher (apically) position. The Pachygaleus cusp is thicker
(labio-lingually) and the teeth are relatively shorter (apico-basally) and broader
(mesio-distally). The Palaeocene tooth in Figure 1 has rather strong basal wrinkles (folds).