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Pachygaleus

CAPPETTA 1992
Extinct Houndshark
Late Paleocene - Mid Eocene
Ordine Famiglia
Carcharhiniformes COMPAGNO 1973 Triakidae GRAY 1851

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 Paleocene (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).


Fig. 1 - Pachygaleus lefevrei
4.7 x 8.2 mm
Aquia Formation (Thanetian - Late Paleocene), Maryland
Fig. 2 - Pachygaleus lefevrei
Nanjemoy Formation (Eocene), Virginia
Fig. 3 - Comparison: Pachygaleus and Galeorhinus
A-I Pachygaleus lefevrei
J-M Galeorhinus aff ypresiensis
Nanjemoy Formation (Eocene), Virginia 

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