Updated 4:31 p.m. ET on February 5, 2019.
Four years after he first came across an unidentified dinosaur in southern Argentina, the paleontologist Pablo Gallina uncovered one of its neck bones and got a surprise.
In 2010, he had found a set of dinosaur teeth in Bajada Colorada. This area is rich in fossils, but because many of them are in fragile condition, Gallina had decided not to expose the teeth any further. Instead, he and his colleagues from CONICET, the Argentine government’s science agency, excavated a large chunk of surrounding earth, packed it in a plaster jacket, and took it back to their lab to carefully extract whatever bones lay within.
Gradually, the team exposed more teeth, a jawbone, and most of the creature’s skull. Then, finally, the neck bone. The six-inch-long vertebra had a pair of huge spines protruding from it, each almost two feet long.
Each spine was probably like the horn of a modern-day antelope, with a thick sheath of keratin (the material in your hair and nails) covering a core of bone. But Gallina thinks that unlike antelope horns, which grow as a single pair from their owner’s head, these spines ran all the way down the dinosaur’s long neck, with one pair per vertebra. It’s as if the animal had a sharp, horny mohawk growing where a mullet should be.
The team named the dinosaur Bajadasaurus pronuspinax—an etymological chimera of Spanish, Greek, and Latin that means “lizard from Bajada with forward-bending spines.” It lived in the very dawn of the Cretaceous period, around 140 million years ago. And Gallina thinks that it likely used its outrageous spines to defend itself from predators.
Bajadasaurus is one of the sauropods—a group of large-bodied, long-necked dinosaurs that include such celebrity species as Brontosaurus, Diplodocus, and Brachiosaurus. More specifically, it’s one of the dicraeosaurs—a family of little-known sauropods distinguished by their neck spines.
The first of these, Dicraeosaurus, was discovered in Tanzania in 1914. Its spines were relatively short, but prominent enough to give the creature its name, which means “two-forked lizard.” For almost eight decades, it was the only known member of its group. Argentine scientists finally described a second species, Amargasaurus, in 1991. And more recently, for whatever reason, dicraeosaurs have been popping up all over the place. Three more were described in the 2000s. Lingwulong, from China, was revealed last July. Pilmatueia, also from Argentina, was announced to the world just last month. That’s seven species, and Bajadasaurus makes eight.
There are almost as many hypotheses about what dicraeosaur neck spines were for as there are dicraeosaur species. Some scientists suggested that they supported a camel-like hump, or that they held aloft a pair of sails, which served to regulate body temperature or signal to mates and rivals. Other researchers reckoned that the spines might have clattered together to make sounds, or supported air sacs connected to the dinosaur’s lungs.
Gallina isn’t discounting any of these ideas, but he argues that “the most logical explanation” is that each spine was its own separate horn, and together, they were used in defense. As dicraeosaurs bent down to graze, their spines would have flared out to provide cover for the vulnerable necks. The forward-pointing spines of Bajadasaurus might have been especially intimidating: They “would represent a disturbing fence for a loitering carnivore,” the team writes in a paper on the discovery.
Admittedly, that’s a lot to infer from just a single set of spines, on a single vertebra. Without the rest of the skeleton, the team can’t say for certain whether such spines really adorned the rest of Bajadasaurus’s neck. They’re basing their reasonable reconstruction on the closely related Amargasaurus—an animal that’s known from a full skeleton, and whose neck spines were just as long and dramatic as Bajadasaurus’s. They differ only in their direction, sloping backwards instead of forward.
Given the similarity between the two animals, Gallina thinks it’s unlikely that Bajadasaurus had only one set of spines, which just happened to be on the one neck bone the team found. It’s also unlikely that the other spines bent in different directions, because that would have stopped the beast from raising or dipping its neck. And it’s equally improbable that the spines Gallina found had become distorted in the fossilization process, because none of Bajadasaurus’s other bones were warped. “We think we’ve done an accurate restoration,” Gallina says.
Bajadasaurus does have a modern equivalent—the potto, a small African primate that also has long, forward-pointing vertebral spines at the base of its neck. “The spines don’t protrude through the skin, but they do make a series of bumps that have been inferred to serve a defensive function,” says Matt Wedel of the Western University of Health Sciences, who runs a blog about sauropod vertebra. “The existence of such a similar defensive adaptation in a living animal is probably the strongest argument for a defensive function in Bajadasaurus.”
“In modern animals that exhibit these types of bizarre structures, they often serve multiple roles, sometimes functioning in display for mates and species recognition, as well as defense,” says Kristina Curry Rogers, a paleontologist at Macalester College. Given that the spines of different dicraeosaurs were so different, “display may have been just as important, if not more important, than defense, but we’ll have to wait for more discoveries to test these ideas more thoroughly.”
Gallina says that the rest of Bajadasaurus’s skeleton is probably still sitting in Bajada Colorada, but the area is such a mess of fossils that “it’s very difficult to recognize what is from this specimen and what is from another.”
But “even if we had the entire skeleton,” Wedel says, “it’s hard to find smoking-gun evidence of a defensive function in a fossil animal. In horned dinosaurs like Triceratops, we can go look for healed injuries on the frill, but short of finding a broken-off Bajadasaurus spine embedded in the face of a meat-eating dinosaur, we will probably not know for certain. Still, that’s part of the lure of paleontology: trying to see how much we can reasonably infer about the lives of these vanished creatures.”
In 2014, Gallina’s team unveiled another new dinosaur from Bajada Colorada. They named it Leikupal after the words for “vanishing family” in the language of the indigenous Mapuche people. It is also a sauropod, and at 30 feet, a relative pip-squeak in a lineage of giants.
At the opposite end of the size spectrum is what other Argentine paleontologists recently discovered, possibly the largest dinosaur of all time—the 130-foot, 69-ton Patagotitan. Other recent discoveries also include: Yi, a small, feathered predator with batlike wings; Kosmoceratops, with its row of comb-over horns; Concavenator, a predator with a small, pyramidal hump over its hips; and Halszkaraptor, an implausible murder-swan with a long, elegant neck; flipper-like arms; and Velociraptor-style sickle claws.
“We are still finding new dinosaurs, and the diversity is increasing year by year,” Gallina says. Which means that we’ll need to make room in the pantheon of exalted dinosaurs for more newcomers as metal as Bajadasaurus.