Il sito italiano sugli squali

Gli squali fossili


Extinct requiem shark
Eocene - Miocene
Ordine Famiglia
Carcharhiniformes COMPAGNO 1973 Carcharinidae JORDAN & EVERMANN 1896

Physogaleus is an extinct genus of requiem shark, which left a fossil record of teeth that are reminiscent of those of Galeocerdo and Rhizoprionodon. In general, the crown is blade-like and distally (weakly or strongly) directed. The mesial cutting-edge continues onto the shoulder and often bears weak serrations. The distal cutting-edge is more upright creating a notch at the distal heel/shoulder. This heel can be strongly serrate with up to four cusplet-like serrations in posterior teeth.

Cappetta (1987) notes that there is strong sexual dimorphism of the lower anterior teeth (the cusps of the male's are laterally compressed), otherwise male and female teeth are of similar design. The basal face of the root can often differentiate upper and lower teeth. In lower teeth, the surface is flat and straight, while in uppers, it is often concave. Positionally, anterior teeth tend to have more erect cusps, few if any distal cusplets, and a stronger lingual root protuberance. In more lateral positions, the cusps become more distally directed and the distal shoulder, more serrate.

Physogaleus teeth have been found in Eocene sediments of Europe, Africa, Asia & North America, and reported from the Oligocene & Miocene of Europe and Miocene of North America. Cappetta (1987) notes that in Europe, P. secundus (WINKLER 1874) & P. tertius (WINKLER 1874) are the most common Eocene representatives of the genus. Kent (1994) attributes P. secundus as the only species of the Chesapeake's Nanjemoy and Piney Point sediments. Case (1994) reported P. tertius and a new species, P. americanus, from the Paleocene & Early Eocene of Mississippi. The teeth illustrated for these two species are indistinguishable from examples referred to herein as P. secundus.

Fig. 1 - Physogaleus secundus
from left to right Upr Anterior: 5.0 x 6.6 mm
Upr Lateral: 5.3 x 8.0 mm Lwr Lateral: 5.2 x 7.8 mm
Lwr Lateral: 5.2 x 5.0 mm Lwr Anterio-lateral: 5.6 x 7.7 mm
Nanjemoy Formation (Ypresian, Early Eocene), Virginia

Fig. 2 - Physogaleus tertius
Left tooth 6.5 x 9.0, right 7.5 x 9.0 mm
Ypresian (Early Eocene) -- Egem, Belgium
From the collection of Marco Maas

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