Sauropods always had size on their side. The largest species, like Supersaurus were so gargantuan that the simple makeup of their muscles, tendons, ligaments, and other tissues would have been quite a task for any predatory to chomp through even with a proffered neck. The fantastic growth rate of these dinosaurs, too, acted as a form of defense. Newly hatched sauropods were Jurassic popcorn, but their growth strategy of rapid bodily inflation offered youngsters the hope of getting to big to easily eaten.
But that's hardly all. The whip-like tails of some sauropods have been interpreted as defensive weapons, for example, and dinosaurs like Shunosaurus even had tail clubs. Now, according to a new paper by paleontologist Pablo Gallina and colleagues, it may be possible to add spikes to their repertoire. Fossils uncovered in the roughly 1
That resemblance may not be coincidental. Many caterpillars have spiky, stinging hairs that look as nasty as they feel. It's a warning to predators. Perhaps, Gallina and colleagues argue, the spikes of Bajadasaurus served in a similar function.
Paleontologists have seen structures like this at least once before. The South American sauropod Amargasaurus – a fairly close relative of Bajadasaurus – sported double-rows of backward-pointing spines jutting from its neck. No one knows why. The spikes look too flimsy to be weaponry, so the traditional alternative explanations have been offered – social signaling, sexual selection, and thermoregulation.
Bajadasaurus is a bit different. First, we know little of this dinosaur. The idea that this dinosaur had was especially spiky neck based on the discovery of a single vertebra with hooked spines and the dinosaur's relationship to Amargasaurus . The real animal could wind up looking more conservative, or even more extreme. Bajadasaurus were covered in extremely long keratin sheaths is based on previous research of Amargasaurus and other dinosaurs.
So what the evidence that Bajadasaurus evolved into a "fence" of forward-pointing spikes for defense? For now, the hypothesis is untested.
Paleontologists have grappled with this puzzle for decades, with many "weapons" – like the horns of ceratopsids – turning out to look better than social signals than spears and shields. And there's even one single reason for having the shape they do among vertebrates. "Bizarre structures" often represent compromises. In the various species of modern antelope, for example, horns are often formed by pressures related to defense, social signaling, sexual competition, and thermoregulation, emphasis in one area creating a different shape than in another. The same would have been true for dinosaurs, so trying to pin down a single reason for an organized structure is likely to be off the mark.
All the same, it's difficult to think of a hungry Early Cretaceous theropod looking at a full -grown Bajadasaurus and wanting to go for the neck. Perhaps the spines had no mechanical defense function at all. Perhaps – in addition to carrying social signals to Bajadasaurus themselves – the spines made the dinosaurs look bigger, more intimidating, or otherwise offered an extra deterrent. This is pure speculation, and it's near impossible to test in an extinct animal, but notion is based upon biological clues in our modern world.
Finding more Bajadasaurus to understand individual variation in spine details, as as well as how the spines changed as baby Bajadasaurus grew up, might provide some of these structures, as they have for the crests of the shovel-beaked hadrosa. A supremely cool new dinosaur has been added to the list. Now our task is to get to know it better.