A well-preserved mosasaur fossil—the first of its kind ever to be discovered in Japan—was from an unusual marine reptile that lived during the Late Cretaceous period and likely dined on squid and glowing fish during the nighttime, according to a new study.

In research appearing this week in the Journal of Systematic Palaeontology, Takuya Konishi, an assistant professor of biological sciences at the University of Cincinnati, and colleagues reported that the 72-million-year-old remains help resolve a biogeographical gap between the Middle East and the eastern Pacific. More importantly though, they reveal that the lizard had unique binocular vision.

The species, identified as Phosphorosaurus ponpetelegans, was smaller than most of its cousins—growing only to about 10 feet long compared while most mosasaurs were up to 40 feet long. The fossil was preserved so well that Konishi’s team found that the creature’s eyes were on the front of its face, allowing it (unlike any of its relatives) to have depth perception.

In fact, the research team’s analysis found that these smaller mosasaurs had completely different eye structures than their bigger cousins, whose eyes were located on the sides of their heads (like a horse). Phosphorosaurus ponpetelegans, on the other hand, had forward-facing eyes similar to those found on modern-day birds of prey or predatory mammals, according to Konishi.

Creature was most likely a nocturnal hunter

“We knew already that most mosasaurs were pursuit predators based on what we know they preyed upon – swimming animals,” the professor said in a statement Monday. “Paradoxically,” he added, “these small mosasaurs like Phosphorosaurus were not as adept swimmers as their larger contemporaries because their flippers and tailfins weren’t as well developed.”

For this reason, the study authors believe that these creatures would have been nocturnal hunters. Binocular vision would have doubled the number of photoreceptors they used to detect light, and the mosasaur’s large eye sockets, indicated that its eyes were big enough to take full advantage of them. Also, since fossils from the ancestors of bioluminescent fish and squid have been found from the same period in the same area, it’s likely the lizard targeted those glowing creatures.

“If this new mosasaur was a sit-and-wait hunter in the darkness of the sea and able to detect the light of these other animals, that would have been the perfect niche to coexist with the more established mosasaurs,” Konishi said. noting that the fossils, first discovered in 2009, were “so unusually well-preserved that, upon separating jumbled skull bones from one another, we were able to build a perfect skull with the exception of the anterior third of the snout.”

“This is not a virtual reality reconstruction using computer software. It’s a physical reconstruction that came back to life to show astounding detail and beautiful, undistorted condition,” he added. Future research, the study authors claim, will examine exactly where this new species fits in the mosasaur’s evolutionary tree.

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Feature Image: Tatsuya Shinmura, Ashoro Museum of Paleontology

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