Onchopristis
numidus, Rostral Spine (Sawfish Tooth)
Order:
Rajiformes, Family: Sclerorhynchidae (extinct family)
Mid Cretaceous
(Albanian, 113 mya)
Location:
Continental Sandstone, S. of Taouz, K'Sar-es-Souk province, Kem-Kem basin,
Moroccan, Sahara
Onchopristus numidus was an ancestor of what we call a sawfish. This fish-like creature lived during the late Cretaceous period. These teeth-like spines ran along both sides of a long snout (rostrum). The rest of the body was a shark-like form. 1 A rostral Spine is a toothlike structure covered in enamel that attached to the bill of a sawfish.The "saw" itself is an elongated rostral projection from the cranium, bearing on each side, a single series of large tooth-like structures. The cartilage encloses 3-5 longitudinal canals or ducts and is strengthened by calcification. The rostral teeth are embedded in deep sockets (alveoli) of this hardened cartilage. 2
Related to the modern day sawfish, the Onchopristis had a long, hard shovel-shaped snout lined on both sides with barbed teeth. This fascinating member of the shark and ray family trolled the murky bottoms of warm Cretaceous seas nearly 100 mya. To gain insight as to how this extinct animal might have lived we can examine the modern day sawfish. Sawfishes are very lethargic animals, spending much of their day nestled in the muddy sea/river floor. At night, they scull slowly through the shallows, using their sensitive saw to find buried prey, which are then raked from the sediment to be consumed. It is useful to view the sawfishes' unique rostrum like a metal detector combined with a clam rake. If small fishes, like mullet, swim past a hungry sawfish, this great ray will launch from the bottom, slashing its toothy weapon rapidly side to side. Gouged by the snout's awl-shaped teeth, injured fishes tumble to the sea floor, now immobilized and easy to catch! Apart from its use in finding and disabling prey, the toothy rostrum is also a weapon of defense. When threatened, sawfishes will smack this jagged sword against attackers, whether they be sharks or fishermen. Generally, though, sawfishes are very gentle animals, preferring to lie quietly, undisturbed. Sawfishes love muddy shallow water, and this is why many people are unaware of them. Few humans, apart from tribal villagers and fishermen venture into sawfish domain. These elasmobranchs possess a remarkable physiological system allowing them to travel from the sea into freshwater at will. Some species seem to spend most of their lives in rivers and lakes! It is likely that sawfishes require a variety of habitats and salinities to complete their lifecycle. Roughly 40 species of modern sawfishes are known; only a handful survive today. 3
References:
1. http://www.rocksandminerals.com/fossil/fossil.htm - Rocks & Minerals
2. http://www.elasmo.com/frameMe.html?file=genera/cenozoic/batoids/pristid.html&menu=bin/menu_genera-alt.html - The Life and Times of Long Dead Sharks
3. http://www.paleodirect.com/mv201.htm - PaleoDirect