Amargasaurus: Beast of the Week

This week we will be checking out a sauropod with a truly striking style!  Introducing Amargasaurus cazaui! 

Amargasaurus was a plant-eating dinosaur that lived in what is now Argentina during the early Cretaceous period, roughly 130 million years ago.  It measured about 33 feet (10 meters) long from snout to tail.  It's name translates to "Amarga reptile" in reference to La Amarga, the geological formation as well as the town near where this dinosaur's bones were discovered in Argentina.  "Amarga" in Spanish means "bitter". 

Watercolor reconstruction of Amargasaurus by Christopher DiPiazza

The most unique and striking feature about Amargasaurus is the fact that it had two rows of upward-facing spines down its neck and part of its back.  These spines were actually part of the animal's vertebrae!  The spines growing out of this dinosaur's neck were pointed and spike-like, but as they go further down the back, they become blunter and flatter.  Nobody is exactly sure what purpose these structures would have served in life.  However, many think they were most likely some sort of display adaptation within the species.  Reconstructions of these spines have varied over the years as scientists studied the fossils and came up with more updated ideas.  The oldest versions had skin connecting the spines, like a pair of fins running down the back.  Then it was argued they were more likely not covered in skin, but individually covered in keratin, forming a series of spikes.  The latest study from 2022 examined the spines more closely, finding that their texture and the growth rings in their cross section suggests that there were fibers connecting them in life, and they were likely covered in some sort of soft tissue, forming a sail-like structure.    

Amargasaurus skeletal mount.

Other interesting features about Amargasaurus is that it actually had a relatively shorter neck proportionally when compared to other sauropod dinosaurs.  Like its relatives, however, it likely possessed a set of teeth concentrated at the front of the mouth that were peg-shaped.  This is a good mechanism for raking leaves and other foliage off of branches while feeding. Only part of the skull was found, unfortunately.  This is common for sauropods with their big, bulky bodies and tiny, delicate heads that are easily destroyed during fossilization.

In 2014, a team of paleontologists actually scanned the inside of the part of Amargasaurus' skull that was found, which included the braincase.  They were able to see the space that would have held the dinosaur's inner ear canals, which would control the sense of balance.  The shape of the inner ears plus how the vertebra fit together suggest that Amargasaurus actually would have held its neck horizontally out in front, rather than upright, as sauropods are often imagined.  The head also would have also been oriented with the snout facing directly downwards.  This doesn't mean that Amargasaurus wasn't capable of moving its head and neck around in different poses depending on its behavior, of course, but rather a suggestion on its most comfortable default resting position.  

That's it for this week!  As always feel free to comment below!

References

Cerda, Ignacio A.; Novas, Fernando E.; Carballido, José Luis; Salgado, Leonardo (March 24, 2022). "Osteohistology of the hyperelongate hemispinous processes of Amargasaurus cazaui (Dinosauria: Sauropoda): Implications for soft tissue reconstruction and functional significance". Journal of Anatomy: joa.13659.

Novas, Fernando E. (2009). The age of dinosaurs in South America. Bloomington: Indiana University Press. ISBN 978-0-253-35289-7.

Paulina Carabajal, A.; Carballido, J.L.; Currie, P.J. (2014). "Braincase, neuroanatomy, and neck posture of Amargasaurus cazaui (Sauropoda, Dicraeosauridae) and its implications for understanding head posture in sauropods". Journal of Vertebrate Paleontology. 34 (4): 870–882.

Upchurch, P., Barrett, P.M, & Dodson, P. 2004. Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 259–322.