Bajadasaurus

Name: Bajadasaurus ‭(‬Bajada lizard‭)‬.
Phonetic: Ba-ha-da-sor-us.
Named By: P.‭ ‬A.‭ ‬Gallina,‭ ‬S.‭ ‬Apesteguía,‭ ‬J.‭ ‬I.‭ ‬Canale‭ & ‬A.‭ ‬Haluza‭ ‬-‭ ‬2019.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Sauropoda,‭ ‬Dicraeosauridae.
Species: B.‭ ‬pronuspinax‭ (‬type‭)‬.
Diet: Herbivore.
Size: Uncertain due to lack of fossil remains.
Known locations: Argentina‭ ‬-‭ ‬Bajada Colorada Formation.
Time period: Berriasian to Valanginian of the Cretaceous.
Fossil representation: Partial skull,‭ ‬jaws,‭ ‬teeth‭ ‬and cervical vertebrae.




       A passing glance at the dinosaur Bajadasaurus would likely bring immediate comparisons to another very popular sauropod dinosaur known as Amargasaurus.‭ ‬Amargasaurus made headlines when it was named because of the large spines that rose out and back from the neck,‭ ‬at the time making it unique amongst sauropod dinosaurs.‭ ‬The discovery of Bajadasaurus however now shows us that Amargasaurus was not the only sauropod dinosaur to have these‭ ‬enlarged spines.‭ ‬However,‭ ‬whereas the spines of Amargasaurus face backwards,‭ ‬those of Bajadasaurus pointed forwards.
       Bajadasaurus is described from very partial remains,‭ ‬only one vertebra is known to clearly show the enlarged spine.‭ ‬This spine is basically an elongated projection of the neural spines that would otherwise be much smaller in other sauropod genera.‭ ‬The neural spines provide two projections that would have been carried side by side,‭ ‬possibly repeating for other vertebrae in the neck,‭ ‬though these other vertebrae are still unknown.‭ ‬The preserved vertebra has been estimated by the original describers to have been the fifth vertebrae,‭ ‬the spines rising up to a length of fifty-eight centimetres.
       The purpose of the spines of Bajadasaurus like in most other creatures is highly speculative.‭ ‬They may have been used for inter species combat between differing individuals,‭ ‬but the spines are not exactly robust,‭ ‬and being directly attached to the vertebrae,‭ ‬not in a good position to withstand lots of abuse.‭ ‬Defence from predators is perhaps another idea,‭ ‬but again they do not seem that strong.‭ ‬Perhaps a mass of spikes facing forwards could have been an impressive visual deterrent to a hungry predator,‭ ‬that would rather not chance an injury with so many spines pointing towards it.‭ ‬Visual display so that Bajadasaurus could recognise others of their species and perhaps those in the best physical condition is perhaps most likely.‭ ‬This could also explain why the spines were lacking in other similar sauropods,‭ ‬and a different orientation in others‭ (‬as mentioned,‭ ‬in Amargasaurus they are similar but face the opposite direction‭)‬.
       Because Bajadasaurus is based upon a small amount of fossils,‭ ‬comparison to‭ ‬other genera is needed to give a better overall picture of this dinosaur.‭ ‬Amargasaurus is a clear choice since it too lived in South America and had a similar neural spine arrangement‭ (‬albeit the opposite direction‭)‬.‭ ‬The spines on Amargasaurus extend from the neck vertebrae but do not carry on to the back,‭ ‬and especially given the forward facing nature of the spines on Bajadasaurus,‭ ‬it is perhaps most probable that the enlarged spines only grew on the neck vertebrae.‭ ‬The horns of Amargasaurus likely had a covering of horn around the bone,‭ ‬as evidenced by the grooves in the bone which could have supported blood vessels to facilitate the horn growth.‭ ‬These grooves are lacking in the known vertebral spines of Bajadasaurus,‭ ‬though they may still have had a hard covering of horn,‭ ‬since exposed bone wouldn’t have lasted long without some kind of protection.




       Bajadasaurus was a dicraeosaurid sauropod dinosaur.‭ ‬Thought to be derived from the earlier diplodocid sauropods dicraeosaurids had reasonably stocky bodies.‭ ‬Thin tails and fairly short necks,‭ ‬at least when compared to other type of sauropod dinosaurs.‭ ‬Dicraeosaurid sauropods are most likely to have been low browsers,‭ ‬feeding upon the lowest growing plants.‭ ‬Inner ear reconstruction of many of these genera‭ (‬when fossil study permits‭) ‬confirms that the resting head angle posture of these sauropods was with the mouth pointing down,‭ ‬not forwards.‭ ‬For most of these genera this had led to speculation that vision was somewhat limited,‭ ‬but the available skull structure of Bajadasaurus has revealed something different.‭ ‬The bones above the eye sockets are angled in such a way that the eyes could have faced forwards even when the head was angled low to the ground.‭ ‬This was an almost unique discovery,‭ ‬with the first time it was identified was in the related dicraeosaurid sauropod dinosaur Lingwulong which was named roughly a year before Bajadasaurus.‭ ‬There is even suggestion that eyes that angled to the crown of Bajadasaurus may have even allowed for a limited scope of stereoscopic vision,‭ ‬something that would be very rare not just for sauropod dinosaurs but for herbivores in general.

Further reading
-‭ ‬A new long-spined dinosaur from Patagonia sheds light on sauropod defense system.‭ ‬-‭ ‬Scientific Reports‭ ‬9:1392:1-10.‭ ‬-‭ ‬P.‭ ‬A.‭ ‬Gallina,‭ ‬S.‭ ‬Apesteguía,‭ ‬J.‭ ‬I.‭ ‬Canale‭ & ‬A.‭ ‬Haluza‭ ‬-‭ ‬2019.

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