When it comes to dinosaurs, you may immediately think teeth, jaws, claws, and the amazing arsenal of weapons wielded by terrifying carnivores. But herbivores didn’t just rock up to the party unarmed; many had their own array of defensive weaponry: triceratops’ horns, for example, or ankylosaurus' tail club. Now we can add long, thin, sharp porcupine-esque spines that would make any meat-eater think twice, thanks to the newly discovered Bajadasaurus pronuspinax.
B. pronuspinax is a new species belonging to the Dicraeosauridae family of sauropods – herbivorous quadrupeds – closely related to the Diplodocidae, famous for their large size and long necks and tails. Bajadasaurus roamed the Earth 140 million years ago, at the beginning of the Lower Cretaceous, right in the middle of the sauropods’ heydey and long before titanosaurs would trample this part of the planet.
Discovered in Argentine Patagonia by researchers from the National Council of Scientific and Technical Research (CONICET) and Maimónides University, in Buenos Aires, this new sample is the most complete skull of a dicraeosaurid yet.
What makes it really special though is its unusual neck spines, which seem to point in the wrong direction. Of the five known species of Dicraeosauridae, Amargasaurus cazaui also has neck spines, but they are much smaller, and point backward like a porcupine. B. pronuspinax has many more spines and they point over its head, some reaching a length of over a meter.
"The functionality of the long spines in the Dicraeosauridae is still controversial among paleontologists. With the discovery of Bajadasaurus we believe that it is possible to shed light on some issues," first author Pablo Gallina, a researcher at CONICET, said.
In a paper published in Scientific Reports, he and his colleagues argue that Bajadasaurus’ spines were used for defense, as they are made from bone and covered in keratin, like a rhino horn, which is much tougher and less likely to fracture on impact than bone.
"We believe that the long, pointed spines – extremely long and thin – on the neck and back of Bajadasaurus should serve to deter potential predators. 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,” Gallina explained. “This leads us to suggest that these spines should have been protected by a corneal keratin sheath similar to what happens in the horns of many mammals.”
They also think that due to the eye sockets being near the top of the head, allowing the eyes to see around and above them, that Bajadasaurus spent much of its time grazing the ground, which could also explain the direction of the spines: as it bent down, the spines would protect the dinosaur's head and vulnerable long neck from being snapped or bitten. However, like many appendages in animals, they may also have had other functions, including regulating heat and sexual selection.
There is still plenty to learn about this lesser known family of dinosaurs, often in the shadow of their more famous relatives, but this new discovery is a great place to start.