Composite Onchopristis (Giant Sawfish) Rostrum

This is a section of the rostrum/bill of Onchopristis an extinct giant sawfish that lived nearly 100 million years ago in what is now Morocco. It's a composite, meaning that while all the fossils are real it's been reconstructed out of a section of bill and individual barbs. It's difficult to even find single barbs intact because most of the material found in this layer of the Kem Kem beds is broken. It's still a really cool fossil.

Onchopristis, or “giant saw”, is a genus of extinct giant sawskate (technical not a sawfish) that lived during the Upper Cretaceous in what is now North Africa. It had a long hard shovel-shaped snout called a rostrum. The saw-like rostrum, lined on both sides with modified tooth-like structures called denticles, were hooked and barbed. Onchopristis had an intimidating, 2 meter long rostrum which it would have used to unearth crustaceans at the bottom of shallow waters like sawfish do today.

We know that for the modern sawfish, the rostrum is covered with electrosensitive pores that allow the sawfish to detect slight movements of prey hiding in the muddy sea floor. The rostrum also serves as a digging tool. Should suitable prey try to swim past, the normally lethargic sawfish springs from the bottom and slashes at it with its saw.

Sawfish also defend themselves with their rostrum against intruding predators such as sharks.

The bazaar looking Onchopristis were frequently torn apart by Spinosaurus when this enormous ray traveled up freshwater streams to breed and lay eggs. Onchopristis probably lived in schools. Crocodiles, Spinosaurus and other fish-eating theropods would have feasted on the 8 meter long rays.

The Kem Kem Beds are famous for yielding a diverse, Late Cretaceous, vertebrate assemblage including fish, reptiles and dinosaurs such as Spinosaurus. These fossils are found in a thin bed that outcrops around the edge of a large plateau near Taouz, Morocco. Local miners collect these fossils by digging narrow tunnels by hand into this plateau following the layer.

A paper on this assemblage can be found at: Vertebrate assemblages from the early Late Cretaceous of southeastern Morocco: An overview

One of the tunnels dug into the Kem Kem beds by local miners following the productive fossil beds.
One of the tunnels dug into the Kem Kem beds by local miners following the productive fossil beds.

Onchopristis numidus
Taouz, Kem Kem Basin, Morocco
Kem Kem Beds
3.8" long, largest barb 2.5"
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