Here is a fine shark from the Cretaceous sublithographic limestone
deposits of Lebanon. Since most of the skeleton of a shark is cartilage,
preservation of such details as seen here are uncommon. The fins
and basic body outline have also been preserved in wonderful detail.
Notice the rough nature of the skin, the result of preservation
of the denticles (‘little teeth”). Many cartilaginous
fish have denticles in the skin; indeed, true teeth may have evolved
from them in the dim past. The denticles of sharks are quite abrasive;
sharkskin (shagreen) has been used by some as a substitute for sandpaper.
The genus is extinct, but has a relative in the modern-day dogfish
Triakis. The other partial specimen (lower right picture - 55 mm)
is a bony fish known as Gaudryella.
shark teeth are abundant in the fossils record, the preservation
of an entire shark (having a cartilageneous skeleton rather than
bones) is an extraordinary rarity. This fossil exemplifies the preservation
often found in the Lebanese lithographic limestone where oxygen
depletion and rapid sedimentation combined to inhibit decay and
enable soft tissue preservation.
see: Class Chondrichthyes