Tuesday, February 12, 2019

Bajadasaurus: Beast of the Week

This week we will be looking at a newly discovered dinosaur that looks right at home in a Tim Burton movie.  Enter Bajadasaurus pronuspinax!

Bajadasaurus was a plant-eating dinosaur that lived in what is now Argentina during the early Cretaceous period, about 140 million years ago.  From snout to tail it would have measured roughly thirty feet long, but this is based on only the few bones of this dinosaur that were actually found.  The genus name translates to "Bahada reptile" in reference to the region in Argentina where its bones were found.  The species name, pronuspinax, translates to "forward-leaning spine" in reference to the spines that grew from its neck.

Life reconstruction of Bajadasaurus in watercolors by Christopher DiPiazza.

Bajadasaurus was a member of the sauropod order of dinosaurs, the well-recognized dinosaurs with small heads, long necks, large bodies, and long tails.  Within that group, Bajadasaurus was a member of the dicraeosaurid family.  Dicraeosaurids were sauropods that flourished mostly in the late Jurassic to early Cretaceous and were relatively small compared to other sauropods.  (if you consider thirty feet small) Dicraeosaurids also tended to have, relatively speaking, shorter necks when compared to those of other sauropods.  Their most diagnostic characteristic is elongated neural arches of some kind. (A neural arch is the top part of a vertebra.  If you run your finger down the back of your neck or your own spine you can feel them in the form of little bumps.)

Skeletal mount of Bajadasurus' skull and neck on display in Buenos Aires.

Elongated neural arches are not rare in the dinosaur world.  Meat eaters, like Spinosaurus and Acrocanthosaurus had them.  The dicraeosaurid sauropod, Amargasaurus, had long, backward-pointing ones on its neck.  Bajadasaurus, however, had extended neural arches unlike any other dinosaur that we know of so far.  Similar to Amargasaurus, it had long, spike-like extensions growing from its neck bones, but they curved forwards, towards the front of the animal, instead of its tail.  The exact evolutionary reason for this is a mystery.  Some suggest this was defense against predators, presenting a wall of pointy things whenever the dinosaur bent its head down to eat low-growing plants or to drink.  Some say they were for display within the species.

Known bones from Bajadasaurus.  Note the single vertebra with the two spines.  Also note the majority of the skull, including teeth.  Image from the most recent paper, published in 2019.


All this being said, it is important to keep in mind that only one neck vertebra of Bajadasaurus has been found so far, sporting two of these long spikes.  Looking at close relatives, like Amargasaurus, the most logical thing to do is assume it had similar structures on the rest of its neck, but as of now we can't know for sure, let alone the exact lengths and shapes of these other spikes, if there were any.  On the flip side, we do have a lot of Bajadasaurus' skull, including its teeth and eye sockets, which is pretty awesome considering sauropod skulls are notoriously the most rarely found parts.  The eye sockets were relatively large and almost perfectly circular, suggesting this dinosaur had decent vision.  The teeth, like those of most sauropods, were concentrated to the front of the mouth, and were shaped like skinny little pegs, ideal for raking vegetation into the mouth to be swallowed.

References

 PA Gallina, S. Apestegu√≠a, JI Canale and A. Haluza, A new long-spined dinosaur from Patagonia sheds light on sauropod defense system , in Scientific Reports , vol. 9, 2019, p. 1392

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