Community College (LRCCD)

Geology & Earth Science Instructor: Arthur Reed, P.G.

Happy Fossil Friday!

Friday March 12, 2021

Xenacanthid, Spined Shark

“One of the most fearsome fossils to come out of the north of England coalfields. This spine stuck out behind the head of a meter-long xenacanthid shark!”

50mm scale overall length

Physical Description: Xenacanthus gets its name from the very large and narrow spike protruding out of the back of its head.. Besides that, the thing most people talk about are its teeth. Xenacanthid teeth are distinctively-shaped: they had a large oval base with two prongs shooting out, making the tooth look V-shaped.

Diet: Xenacanthus’s bizarre teeth may hint at a diet of crunchier foods. It likely ate fish and small invertebrates in the waters it lived, as well as potentially the carcasses of anything that drowned.

Behavior: Xenacanthus’s body is not well-equipped for fast swimming. Its pectoral and pelvic fins almost look limblike, and may have potentially been used to help maneuver (or “walk”) around river bottoms like modern epaulette sharks. Xenacanthus likely sat in the muddy bottoms of the rivers it lived in, waiting for prey to swim on by.

Ecosystem: Xenacanthus lived in shallow freshwater environment such as seasonal rivers.

Other: Xenacanthus evolved in the Permian, and amazingly made it through the Great Dying. They were a lot more common in the Permian, but xenacanthids made it through to the end of the Triassic (when they were apparently done in by the end-Triassic extinction).

(no narration in this video)

Approximated position of the continents at the time of the xenacanthid shark.

Purple dots indicate two discovery sites in Texas and India.

Adapted from ‘Dinosaur A Day’ and National Museum Cardiff in Wales