A newly discovered mosasaur species had teeth more like certain sharks than anything from the lizard family. The discovery reinforces something paleontologists have started to suspect – large marine life was flourishing, not declining, immediately before the asteroid that ended the Cretaceous Era.

Dr Nick Longrich of the University of Bath in the UK has helped describe and name Xenodens calminechari in the journal Cretaceous Research. Unlike the gigantic hero/villain of Jurassic World (or even its closest real counterparts), this mosasaur was similar in size to a small porpoise, but it co-existed with many much larger marine predators.

“Sixty-six million years ago, the coasts of Africa were the most dangerous seas in the world,” Longrich said in a statement. “Predator diversity there was unlike anything seen anywhere else on the planet. The new mosasaur adds to a rapidly growing list of marine reptiles known from the latest Cretaceous of Morocco, which at the time was submerged beneath a tropical sea.”

The authors think Xenodens survived in this competitive environment by literally carving out its own dietary niche.

The discovery was so unexpected even the title of the paper describing it calls the creature “bizarre”. “[The] teeth form a unique dental battery in which short, laterally compressed and hooked teeth formed a saw-like blade,” the authors wrote, before pointing out that nothing like this has been seen before among air-breathing animals. However, Dr Longreach noticed the resemblance to the sleeper sharks he sometimes caught growing up in Alaska.

Longrich and co-authors argue such distinctive mouth “Implies a previously unknown feeding strategy, likely involving a cutting motion used to carve pieces out of large prey, or in scavenging.”

However, sleeper and dogfish sharks also use their similar teeth to catch smaller fish, sometimes cutting them in half. With teeth Longrich said could “slice through anything,” the authors think Xenodens probably combined a food supply competitors couldn't touch with more generalist feeding.

Co-author Dr Nathalie Bardet of the National Museum of Natural History in Paris added, “I have been working on mosasaurs for over 20 years ...I must admit that among the 10 species that I know, this one has a so unusual and extraordinary dentition that at the beginning I thought it was a chimera reconstructed with different fossils!”

We're in a golden age of mosasaur discoveries. The new discovery comes just three months after the announcement of a much larger mosasaur from the same era and location adapted to catching fast-moving prey. That, in turn, followed just a month after the unveiling of a giant with jaws of death almost as long as Xenodens' whole body from the other side of the Atlantic.

All this mosasaur madness demonstrates the oceans were capable of supporting a vast array of large predators immediately before the Chicxulub asteroid struck. There has long been debate as to whether dinosaurs were in decline in the lead-up to the impact, with a staunch minority of palaeontologists arguing they were doomed, with or without the asteroid. However, this view has taken several hits recently and doesn't fit well with the astonishing productivity of the Late Cretaceous oceans.