Dinosaurs ruled the land during the Jurassic period. But at sea, it was the age of ichthyosaurs—so-called "sea monsters" that looked like a cross between a narrow-nosed crocodile and an ill-tempered dolphin.
Ichthyosaur (pronounced ik-thee-uh-sawr) means "fish lizard" in Greek. These predatory reptiles swam the ancient oceans in roles similar to those of whales and sharks today.
Now, a team of scientists in Scotland has announced the discovery of a new genus of ichthyosaur that was approximately 14 feet (4.3 meters) long, the size of a small motorboat. (Also see "First Amphibious 'Sea Monster' Found; Fills Evolutionary Gap.")
"We've discovered a totally new species of big reptile that lived in the ocean about 170 million years ago," said Stephen Brusatte, a paleontologist at the University of Edinburgh. "It's also the first ichthyosaur ever found in Scotland"—which is already famous for its mythical sea monster, nicknamed Nessie.
Brusatte and his colleagues named the new ichthyosaur Dearcmhara shawcrossi, a tribute to amateur collector Brian Shawcross, who originally found the fossils on Scotland's Isle of Skye (map). Shawcross donated the fossils—which revealed parts of the animal's arm, back, and tail—to the University of Glasgow's Hunterian Museum so they could be studied.
Changing of the Guard
The new species is intriguing because it shakes up what scientists thought about ichthyosaur evolution, the team said. (Explore an interactive sea-monster time line.)
D. shawcrossi is considered a small and primitive ichthyosaur—some grew to be bus-size—that thrived during the little-understood Middle Jurassic, which lasted about 15 million years.
From fossils dating before and after this period, scientists know that this was a time of great upheaval below the waves.
"After the Middle Jurassic, there's a new type of ichthyosaur—larger, more advanced—that comes onto the scene and takes over, and it becomes dominant all over the world." (See "New Sea Monster Found, Rewrites Evolution?")
Since the newfound ichthyosaur is one of the smaller, more primitive variety, this hints that the transition to bigger sea monsters probably occurred a little later in the Jurassic period than experts had previously thought.
It's unknown why this transition to bigger, badder ichthyosaurs occurred, but finding D. shawcrossi may indicate that the shift was gradual, and not due to a sudden event like a shift in ocean temperature or a big volcanic eruption.
Ichthyosaur fossils themselves aren't particularly rare. New samples are popping up all the time, from southern Chile to western Russia. However, ichthyosaur specimens—not to mention most fossils—from the Middle Jurassic are few and far between. Scientists don't know why—it "just so happens that some periods of time give better samples than others," Brusatte said.
"It's just dumb luck really, because the fossil record is so imperfect," he added. "And Scotland just happens to be one of the places where we have good samples from the middle part of the Jurassic."
Aubrey Jane Roberts, a postgraduate researcher at the U.K.'s University of Southampton and an ichthyosaur expert, said the time period in which D. shawcrossi lived makes the discovery all the more exciting. (Read "When Monsters Ruled the Deep" in National Geographic magazine.)
"It fills in a very important gap in our understanding of the evolution of these animals," said Roberts.
"What's interesting about Scotland is it shows ichthyosaurs there were sort of behind the rest of the world. The shift [to bigger ichthyosaurs] was already happening in Alaska and South America, but it took a bit longer in Europe."