Bajadasaurus pronuspinax
In late 2018 Gallina et. al published their description of a new dicraeosaurid sauropod from Argentina and this species was crazy, even by dicraeosaurid standards (which is pretty darn crazy)!
Bajadasaurus pronuspinax was revealed to be superficially similar to its sister taxon Amargasaurus cazaui, which I reconstructed some years ago.
But b. pronuspinax takes weirdness to the next level, as instead of having a recurved, posteriorly-oriented set of bifurcated neural spines, b.pronuspinax boasts a double-row of spines pointing forward!
Stories like this are mana from heaven to palaeoartists, so I, like many others, set about researching the taxon and trying to work out how on earth to reconstruct it. This is difficult in b.pronuspinax and a. cazaui in that there is no real consensus on whether the grossly-elongated neural spines in the cervical vertebrae should be depicted sheathed in keratin, tapering into a crown of horns; or if they would be sheathed in soft tissue, supporting a sail?
Arguments in the scientific literature have been put forward in favour of both options. The sail might on first-glance appear to be the more plausible solution; dicraeosurids (and other sauopods) with more modest neural spines boasted well-muscled ridges along the length of the body, both supporting the weight of the animal and perhaps also providing a broad canvas for display.
Other groups of dinosaurs also boast an arsenal of crests, plates and shield-like structures which double up as attachment points for broad muscles and/or intraspecies display structures, but double-rows of very thin and fragile-looking keratinous horns are seldom to be found, in dinosauria or elsewhere in the fossil record. The only vaguely close analogue might be the paired spines (thagomizers, if you prefer) along the tails of stegosaurids. However, these are relatively short, thick and straight, whereas the elongated neural spines of dicraeosaurids are long, thin and curved; not suitable for bearing the brunt of any applied force. So if they supported horns, what kind of purpose could they possibly serve?
However, the sail theory may appear the more plausible of the two propositions, but it has its problems too. Notably the greatly restricted vertical motion in a neck with such a thick and cumbersome structure would seem to be highly disadvantageous. Even though dicraeosaurids had relatively short necks (by sauropod standards!), even an animal specialising in tree-top of mid-line grazing must lower it's head to drink from time to time.
So, the jury is still out and may well continue to be so for a very long time (unless we are lucky enough to find a specimen from either taxa with soft-tissue integument impressions remaining). However, despite first impressions, the case for horns currently slightly holds sway, thanks in part to evidence highlighted by Schwartz et. al in their 2007 paper on the subject. In this paper, the authors demonstrate that a. cazaui:
Bajadasaurus pronuspinax was revealed to be superficially similar to its sister taxon Amargasaurus cazaui, which I reconstructed some years ago.
But b. pronuspinax takes weirdness to the next level, as instead of having a recurved, posteriorly-oriented set of bifurcated neural spines, b.pronuspinax boasts a double-row of spines pointing forward!
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| Bajadasaurus pronuspinax, copyright Alice V S Turner 2019 |
Stories like this are mana from heaven to palaeoartists, so I, like many others, set about researching the taxon and trying to work out how on earth to reconstruct it. This is difficult in b.pronuspinax and a. cazaui in that there is no real consensus on whether the grossly-elongated neural spines in the cervical vertebrae should be depicted sheathed in keratin, tapering into a crown of horns; or if they would be sheathed in soft tissue, supporting a sail?
Arguments in the scientific literature have been put forward in favour of both options. The sail might on first-glance appear to be the more plausible solution; dicraeosurids (and other sauopods) with more modest neural spines boasted well-muscled ridges along the length of the body, both supporting the weight of the animal and perhaps also providing a broad canvas for display.
Other groups of dinosaurs also boast an arsenal of crests, plates and shield-like structures which double up as attachment points for broad muscles and/or intraspecies display structures, but double-rows of very thin and fragile-looking keratinous horns are seldom to be found, in dinosauria or elsewhere in the fossil record. The only vaguely close analogue might be the paired spines (thagomizers, if you prefer) along the tails of stegosaurids. However, these are relatively short, thick and straight, whereas the elongated neural spines of dicraeosaurids are long, thin and curved; not suitable for bearing the brunt of any applied force. So if they supported horns, what kind of purpose could they possibly serve?
However, the sail theory may appear the more plausible of the two propositions, but it has its problems too. Notably the greatly restricted vertical motion in a neck with such a thick and cumbersome structure would seem to be highly disadvantageous. Even though dicraeosaurids had relatively short necks (by sauropod standards!), even an animal specialising in tree-top of mid-line grazing must lower it's head to drink from time to time.
So, the jury is still out and may well continue to be so for a very long time (unless we are lucky enough to find a specimen from either taxa with soft-tissue integument impressions remaining). However, despite first impressions, the case for horns currently slightly holds sway, thanks in part to evidence highlighted by Schwartz et. al in their 2007 paper on the subject. In this paper, the authors demonstrate that a. cazaui:
- is likely to have possessed supravertebral pneumatic diverticula enclosed between its bifurcated neural spines (a feature indicated by the presence of supramedullary diverticula in dicraeosaurids), indicating that this portion of the cervical spines at least would have to be enclosed in soft tissue
- there is no clear osteological correlate (points of attachment) for the supraspinal ligament which runs the dorsal length of a sauropod's body and would normally attach at the dorsal tips of the cervical neural spines, indicating that the distal portion of the spines was not encased in soft tissue
- rugose striations are instead present along roughly two-thirds of the distal length of the cervical neural spines, consistent with keratinous sheathing of horn cores in extant taxa
All things considered, these observations indicate that a. cazaui (and most likely b. pronuspinax) can be restored with spines supporting a sail (or ridge might be a more appropriate term?) over the proximal third of the spines' length, tapering into heavily-sheathed horny structures thereafter. As well as fitting with the current fossil evidence, this reconstruction also goes some way towards solving the issues identified with each approach when taken individually: the limited extent of soft tissue along the length of the spines allows a greater degree of flexibility to be maintained and the added support provided by said soft tissues would strengthen the otherwise spindly-looking horns.
So, that's the science: now for the creative bit! Having conducted some research, I found that b. pronuspinax would most likely have lived in a well-watered environment and that Nypa palms would be an appropriate contemporary plant species to create the backdrop. I found that the height of Nypa matched that of b. pronuspinax pretty well and found that the extended horny spines, with a fine, stripy integument provided great camouflage in amongst a forest of palms.
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| Preparatory sketch for b. pronuspinax |
From there, I performed my usual ritual of calculating above and side-views of the imagined environment, including the height of the trees and subjects, the depth of the water, consistency of the soil and weather conditions for the scene. I then drew the linework on layout paper, scanned that in and printed the result (at super-low opacity) onto 220gsm cartridge paper. To achieve the wash, I experimented with spray-bottles, but found I got the best result with a good-quality sponge. The finished piece was executed in watercolour pencils, acrylic inks and finished with touches of acrylic paint.
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| Bajadasaurus pronuspinax, copyright Alice V S Turner 2019 |
There are things I'm not so happy with in this image, but given the huge technical challenge it presented, I am happy overall with the result. I have learned a number of lessons that can be applied to my next planned life-restoration, which will also feature a forested area with a large body of water!
One issue I had was that I wanted the water to be murky, partly because it suits the environment, but also because reflections don't show up so clearly in flowing, cloudy water! However, the lack of clear reflections from the subjects just doesn't quite sit right with me now that the work is finished and there is little I can do to redress that issue.
That being said, I am content that my reconstruction of the subjects and their environment is reasonably accurate according to the information currently available. I'm looking forward to finally being able to move on to my next challenge!
Sources:
A new long-spined dinosaur from Patagonia sheds light on sauropod defense system
Pneumaticity and soft−tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods
The Effect of Intervertebral Cartilage on Neutral Posture and Range of Motion in the Necks of Sauropod Dinosaurs
Spiky sauropods
Early Cretaceous palm pollen tetrads from Patagonia, Argentina
The Cretaceous flora of the Neuquén Basin, its paleoenvironmental and paleoclimatic significance
Pneumaticity and soft−tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods
The Effect of Intervertebral Cartilage on Neutral Posture and Range of Motion in the Necks of Sauropod Dinosaurs
Spiky sauropods
Early Cretaceous palm pollen tetrads from Patagonia, Argentina
The Cretaceous flora of the Neuquén Basin, its paleoenvironmental and paleoclimatic significance
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