Paleontologists in Argentina have uncovered a dinosaur unlike anything ever seen before. Alive some 140 million years ago, these majestic herbivores featured long, forward-pointing spikes running along their necks and backs. These spikes may have served a defensive role, but their exact purpose now presents a fascinating new mystery.
New research published this week in Scientific Reports describes a new species of dinosaur its discoverers are calling Bajadasaurus pronuspinax (pronounced “BA-HAD-AH-SAURUS” “PRONE-OO-SPIN-ACKS”). The first half of its binomial references to the geological formation where its fossils were found, the Bajada Colorada Formation in Northern Patagonia, Argentina. The latter part of its name means “bent over forward spine,” owing to its most distinctive feature. The fossilized remnants of this extraordinary creature, including a nearly complete skull with some teeth, were uncovered in 2013 by paleontologists from CONICET, Universidad Maimónides, and several other institutions.
Bajadasaurus was a sauropod, a wildly successful group of long-necked, four-legged dinosaurs. A Lower Cretaceous dinosaur, it lived 140 million years ago in what is now Argentina, and it belonged to a subgroup of sauropods called dicraeosaurids—medium-sized sauropods with distinctive vertebrae and long spines along their necks and backs.
Analysis of the Bajadasaurus skull and teeth suggests they grazed on low-lying plants. Their eye sockets were located near the roof of the skull, allowing them to keep watch for predators while they munched on foliage. In the beautiful art produced by Jorge A. González, a small pterosaur can be seen perching on a Bajadasaurus spike—a nice touch, given how prolific these winged reptiles were in South America at the time. Reconstructions of the spikey beast were recently unveiled at the Cultural Science Center in Buenos Aires (pictured above).
Prior to this latest discovery, paleontologists had uncovered another South American dicraeosauridae with spikes, Amargasaurus cazaui. This sleek-looking sauropod lived around 15 million years after Bajadasaurus, but its spikes were much shorter and they leaned backward instead of forward. Bajadasaurus is notable both for the size of its spikes and their forward-leaning orientation. The longest of the rod-like neural spines measured nearly 5 feet in length, close to 150 centimeters.
“We’re barely into February, but Bajadasaurus might end up being the most awesome dinosaur of 2019. The name looks a lot like Badassasaurus, which is actually pretty fitting, as this looks like a punk dinosaur,” Steve Brusatte, a University of Edinburgh paleontologist not directly involved with the research (though he edited the paper for Scientific Reports), told Gizmodo. “The long, spindly spikes sticking out of the neck give the appearance of a Mohawk haircut, or the spiky hair of Johnny Rotten. I can’t help but think that the spines functioned in the same way as Johnny Rotten’s hair: to get attention. These must have been display structures, to attract mates or intimidate rivals, or maybe to rock out in other ways that only the dinosaurs would have known.”
Indeed, the exact function of the spikes isn’t clear. Possibilities include heat regulation (an issue for large-bodied sauropods), sexual display (horns to make dinos horny), a fat reservoir (the fat stores would be located between the spikes, and similar to a camel’s humps), and defense against predators. The authors of the new study, led by Pablo A. Gallina from Universidad Maimónides, favor the idea that the spines served as “passive defense structures.” Any would-be predator, the authors surmised, would risk impaling themselves on these formidable structures during an attack. For that hypothesis to work, however, the long spines would need to be strong enough to avoid shattering or fracturing.
“We believe that the long, pointed spines—extremely long and thin—on the neck and back of Bajadasaurus... should serve to deter potential predators,” said Gallina in a CONICET statement. “However, we think that if they were only bare bone structures or covered only with skin they could have broken or fractured easily with a blow or when attacked by other animals. This leads us to suggest that these spines should have been protected by a corneal keratin sheath similar to what [is observed] in the horns of many mammals.”
Brusatte isn’t convinced.
“The paleontologists who described the new dinosaur suggest that the spines may have been used for defense, but it’s hard for me to imagine that such thin, delicate, gaudy structures would have been much use in deflecting the bite of a big meat-eating dinosaur,” said Brusatte. “It’s an interesting idea, and maybe the authors are correct, but I think display is much more likely.”
Eric Gorscak, a postdoctoral research scientist at The Field Museum in Chicago who wasn’t affiliated with the new study, said “Bajadasaurus is certainly a bizarre discovery,” but like Brusatte, he’s skeptical about the authors’ defense hypothesis.
“Their reconstruction is somewhat speculative as it is based on only one recovered neck vertebra with the curved neural spines,” Gorscak told Gizmodo. “The trouble with such unique features in extinct animals is that there are rare, if any, living examples to compare to better understand potential functions. But at the very least, Bajadasaurus demonstrates that life will find a way to modify pre-existing structures in response to ever-changing ecological and biological demands—even if we’re not entirely sure what those were.”
Stephen Poropat, a paleontologist from Swinburne University of Technology in Australia, thought the new discovery was significant owing to how much of the skull was recovered, but he was “intrigued” by the significance the authors afforded to the forward-pointing spines, which appeared on only one of the three neck vertebrae recovered.
“They seem not to consider the possibility that these processes [fossils]—which are very long and exceedingly thin—might have been subjected to some degree of post-mortem deformation due to geological processes,” Poropat told Gizmodo. “In other words, when Bajadasaurus was alive they might have pointed forward to a lesser degree, or not pointed forward at all.”
He also said it’s difficult to know the kind of soft tissue that once covered these spines. He agreed that keratin is a possibility, as the authors suggest, but it’s also possible the spines were surrounded by soft tissue, or used to support a frill, he said.
“It is important to remember that these structures were actually part of the vertebrae of these animals, unlike the plates of stegosaurs or the armor of ankylosaurs, which were separate bones, not fused to the spine,” Poropat said, adding that “the conclusions the authors draw about Bajadasaurus using its spines for defense are speculative.”
A reasonable next step for the authors would be to put their theories to the test, and conduct some experimental paleontology. This could be done using computer simulations or with materials that approximate the strength of the Bajadasaurus spikes. Similar experiments have been done before, for example, with researchers using models to estimate the maximum running speed of Tyrannosaurus rex before it would snap its legs with its tremendous bulk.
The exact purpose of the spikes aside, there’s no question Bajadasaurus is one of the more spectacular dinosaurs we’ve seen in quite some time. It’s incredible to think of all the things we’re still learning—and still hope to learn—about the remarkable creatures that lived long before humans.
This post was updated to include comments from Stephen Poropat.