Borealopelta (PNSO, 2020)

Informally known – before publication – as “Suncor nodosaur”, Borealopelta markmitchelli (Brown et al., 2017) is a nodosaurid described only recently, but which has immediately gained a great deal of attention from enthusiasts (for those interested: it appears in Jurassic World Evolution, even though it is called “Nodosaurus”). Why? It is easy to say: not only is it one of the best preserved nodosaurs in the world, but even the scales and keratin cases that covered its armor are preserved, allowing – through mass spectroscopy – to reconstruct the probable pigmentation of the animal in life. We even know the contents of his last meal, thanks to material found inside his stomach. Such a discovery could not escape the companies that produce models, and in fact Collecta and Kaiyodo were the first to make their Borealopelta. In 2020, it was PNSO’s turn

A single specimen of Borealopelta (TMP 11.033.0001) is known to science. The fossil is not complete and shows the head, neck, body and sacral region, a complete (right) forelimb and a fragmentary one and part of the foot. The remains are spectacular and, looking at them from certain angles, one almost has the impression of being in front of a sleeping animal, ready to wake up at any moment. Let’s see what the PNSO test was like.

The skull has the characteristic “sheep” shape of the skulls of nodosaurids. The fact of being in front of an armored animal allows us the rare opportunity of being able to examine some of its bone characteristics also in the model. Among the apomorphies (derived characters that are diagnostic of this animal and allow to distinguish it) of Borealopelta there are the presence of a hexagonal plate in the frontoparietal region (in practice, between the eyes of the ankylosaurus) which in the model is distinguishable, under a coverage of smaller scales; and the length of the jugal plate, greater than the orbit. Other details – such as the fact that the jugal plate has a pointed apex – are unfortunately too fine to be assessed at this scale.

Comparison with the fossil. From Wikimedia

Not only in the skull can apomorphies be observed: another characteristic of Borealopelta is that the cervical (neck) and thoracic osteoderms form transversely continuous bands, while longitudinally they are clearly separated by a strip of polygonal scales. Borealopelta osteoderms can be organized into three regions: cervical (three bands), thoracic (twelve bands) and sacral (at least eight bands). We will follow the description in Brown, 2017.

The three cervical bands are present while, despite my efforts, I can only count eleven chest bands (but I could be wrong); counting the sacral ones is a feat beyond my strength. In the fossil, each of the three cervical bands is made up of six osteoderms, and this is also the case in the PNSO model. In correspondence with the strip of polygonal scales mentioned above, there are two “transition” spines on the sides of the body. At this point the thoracic osteoderms begin: the first row has six on each side, including the parascapular spine, the largest osteoderm of Borealopelta; a second row ending in a smaller lateral spine is followed by a third row of six osteoderms, smaller than the others and not reaching the hips. The fourth and fifth rows repeat the structure of the second, while again the sixth does not reach the side. From the seventh onwards, all the thoracic bands repeat the pattern of the second. All this is painstakingly reproduced in the PNSO model. Below the line of the hips he has inserted two more rows of osteoderms (which become three on the hind limb): they are not preserved in the fossil and do not appear in the reconstructions of this animal. This is probably speculation. I suggest caution in handling the model because, if the parascapular spines are blunt, the same cannot be said of some of the smaller osteoderms which, if carelessly grasped, can result in painful punctures.

Comparison with fossil armor (modified from Brown, 2017)

The posterior portion of Borealopelta’s body is not preserved, but it is reasonable to assume that whoever made the model (a sculptor in Zhao Chuang’s atelier) used related genres, such as Europelta, as a basis. Osteoderms covering the tail are, however, relatively standard for a non-Polish nodosaurid, with a single row of not excessively large spines on each side. The abdominal region is covered by small scales similar to those present in the interstices between the bands of the dorsal armor. The right forelimb is preserved in the fossil and has some osteoderms along the humerus, ulna and radius, in particular two in the shape of a spine on the lower part of the leg. For unknown reasons, the sculptor PNSO decided to add a third osteoderm. The hand, typically for a nodosaurus, has five fingers (as for all dinosaurs, only the three innermost ones have claws), while the hind legs have four. The hands have, correctly, the vague open horseshoe shape that tends to be common in quadrupedal dinosaurs (as opposed to an elephant / rhino hand as is often seen).

The keratinous coating of the osteoderms of the Borealopelta fossil is highly pigmented and the authors suggest a reddish discoloration due to pheomelanin. Some osteoderms, on the other hand, have less pigmentation, which results in an observable pattern in the living animal. Unfortunately, while the promotional photos clearly showed this color difference, it did not translate into the final model, whose back is uniformly reddish brown – except for slightly darker halos between cervical osteoderms and in the region between cervical and thoracic osteoderms. On the other hand, another area that presented a different color was the large parascapular spine, which was lighter. In the PNSO model it was chosen to actually represent it with a gray, but the tip – which a lucky fracture of the fossil shows to be made entirely of keratin – is instead black, perhaps in analogy with the keratin covers of the horns of modern mammals.

The organic film that allowed the staining to be reconstructed ends, in the sacral region, just beyond the outermost osteoderms: this probably indicates that the ventral region was lighter, a condition called countershading and visible in many current animals – where it is useful to hide the creature to predators. The publication underlines the ecological implications of the fact that a dinosaur with an estimated mass of 1500 kg (the tonnage of a black rhino, well beyond the threshold at which land mammals exhibit countershading) needed cryptic coloring, possibly due to pressure. predatory. It can also be seen in the PNSO model, even if the detachment is perhaps excessively clear: this impression is given by the fact that the underside completely lacks the dark wash present on the sides and which brings out the details. Here too, greater attention would not have hurt, especially at the level of the forelimbs, where the dividing line is practically straight.

Ultimately – despite the fact that we could do better, especially as regards the coloring – the Borealopelta PNSO is certainly one of the best nodosaurid models in circulation, and for the twenty euros required it represents a real bargain!

Bibliography:

Brown C.M.; Henderson D.M.; Vinther J.; Fletcher I.; Sistiaga A.; Herrera J.; Summons R.E. (2017)  An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics Current Biology. 27: 2514–2521

Brown C. M. (2017) An exceptionally preserved armored dinosaur reveals the morphology and allometry of osteoderms and their horny epidermal coverings. PeerJ. 5: e4066

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