Pycnodontiform

Pycnodontiform is an extinct order of ray-finned fishes that lived from the Late Triassic to the Eocene epochs. These fish are characterized by their highly specialized dentition, featuring crushing, molar-like teeth arranged in dense plates. This dental adaptation suggests a diet of hard-shelled prey such as mollusks and crustaceans.

Pycnodontiforms typically possessed a deep, laterally compressed body, often with a rounded or rhomboid outline. Many species had a prominent dorsal fin and a forked tail fin. Their scales were often rhomboid and tightly interlocking, forming a robust armor. The pectoral fins were usually well-developed and used for maneuvering, while the pelvic fins were often reduced or absent.

Fossil evidence for pycnodontiforms is widespread, with remains found in marine deposits across the globe. They inhabited a variety of environments, from shallow coastal waters to deeper offshore areas. Their abundance and diversity in Mesozoic seas indicate they were a successful and important component of ancient marine ecosystems.

The group experienced a significant diversification during the Jurassic and Cretaceous periods. However, their numbers and diversity declined sharply following the Cretaceous-Paleogene extinction event, and the last known pycnodontiforms disappeared in the Eocene. The exact reasons for their extinction are debated, but likely involved changes in marine environments and food availability.