Amargasaurus: Sail or Spines?

Although the awesome Amargasaurus cazaui isn’t as famous as some sauropods, say, Brontosaurus (which is a recognised name now, by the way!), the creature’s distinctive appearance has made it increasingly popular. I mean, who couldn’t notice the sail on it’s back. Sail? Or spines? This is where it gets confusing.

amargasaurus
Spines or Sails? Spine by Nobu Tamura, Sails by Wikimedia user ArthurWeasley

I’m going to start with a brief overview of the dinosaur. Amargasaurus was discovered in  1991 by Leonardo Salgado and José Bonaparte in Argentina. It was a diplodocid sauropod dinosaur, a herbivore, and grew to ten metres in length. It lived in the Early Cretaceous. It was pretty staple for a sauropod apart form the two rows of spines/sails that ran down across its back. Yes, two rows, although it’s hard to see in most pictures.

The two main theories for the spikes on its back looked like in life. Some beleive that they were covered in a think covering of skin – a sail – sort of like that of Spinosaurus. Others think that there is no skin whatsoever, and that the spikes are capped in horn as spines.

The sail idea is based on the fact that if sail extended to the neck, it would be hard for the animal to drink, and therefore they would have to be loose to let the animal be flexible. Before we continue, we need to discuss why on Earth the animal would evolve the spikes in the first place.

 

amargasaurus skeleton
Amargasaurus skeleton. Photo by Gastón Cuello

 

There are many reasons an animal would evolve. Defence from predators is one, but if they were built for defence surely they would not only be at the top but also at the side, and more varied? Another solution is thermoregulation, but not only is that theory old but surely another sauropod would have done some form of sail as well? Also the two sails next to each other would have blocked light from each other, giving each sail the end value of half a sail.

The most commonly accepted idea is that they were for show. But what type of show? If they were sails, they could display bright colours. Just as likely, as spines they would have rattled together to make threatening sounds. In the end, what most people have settled on when they do Paleoart is having the spikes on the neck as spines and the spikes on the back as sail. To conclude, both theories seem equally plausible, and maybe even a bit of both.

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