Named By: P. A. Gallina, S. Apesteguía, J. I. Canale & A. Haluza - 2019.
Classification: Chordata, Reptilia, Dinosauria, Saurischia, Sauropoda, Dicraeosauridae.
Species: B. pronuspinax (type).
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.
passing glance at the dinosaur Bajadasaurus would
immediate comparisons to another very popular sauropod
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
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.
- 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.