One of the merits of a monothematic line such as the three Beasts of the Mesozoic series is that it features, alongside better-known genera, less popular but equally interesting animals. Such as Bistahieversor, a Tyrannosauroidea that lived about 75 million years ago in North America.

Bistahieversor is sold in a plastic and cardboard box, decorated with an artwork by Raul Ramos that shows it preying on Pentaceratops. The inside of the box is similar to the illustration in both theme (a misty wood) and colour and can be used as a background for displaying the model.

Inside the box, there are two levels of plastic tray: one with Bistahieversor, its tail (detached, for space reasons) and the optional feet (three pairs, to recreate the gait sequence) and one with the base and the articulated hindlimbs. There is also a plastic bag with a trading card and assembly instructions (nothing too difficult, just remember to heat the tail base with hot water or a hair dryer it and to rotate the optional feet to detach them from the legs). The model and its accessories are held in place by plastic ties: a pair of small scissors is recommended to remove them.

The Bistahieversor sculpture is work of Jacob Baardse and is based on Scott Hartman’s restoration. Ths restoration itself is heavily based on that of Lythronax made by the same author (the two skeletals are literally almost superimposable). Lythronax is the base for the BOTM Bistahieversor, too: the two models share the same sculpture with the exception of the head of the neck. So, is Lythronax a good base for Bistahieversor? As often with paleontology, it depends. The only part of the holotype and the only known adult specimen of Bistahieversor that’s described and illustrated, at the moment, is the skull, although part of the pubis, of the femur and the hindlimb are also known. Therefore, in order to restore the animal one needs to consider its most close relatives. Some of the earlier analyses (e.g., Brusatte et al. 2010) classified Bistahieversor as a Tyrannosauridae that sit between Teratophoneus and Lythronax, and Scott Hartman’s restoration is based on that. However, other, more recent phylogenies (e.g. Voris et al. 2020), found Bistahieversor as a more basal animal, a Tyrannosauroidea just outside Tyrannosauridae (remember that clades with the -dae suffix are inside a bigger -oidea “box”). Using animals such as Appalachiosaurus, another Tyrannosauroidea close to Tyrannosauridae, to fill the holes, rather than Tyrannosauridae, results in a more slender animal. Not an abysmal difference from Hartman’s reconstruction, however, so to a large extent we can consider the proportions of the BOTM model plausible, pending new discoveries.

As we said, the only adequately described and figured part of Bistahieversor is the skull, which we can compare with that of the BOTM model. Most of the macroscopic features of Bistahieversor’s skull, such as the relatively thick mandible compared to the skull and the high jaw (if Bistahieversor truly sits outside Tyrannosauridae, it would be the first Tyrannosauroidea to feature this trait, which gives Tyrannosauridae skulls their typical silhouette) are respected. This is lampshaded comparing the Bistahieversor model with another BOTM Tyrannosauroidea-not-Tyrannosauridae, Dryptosaurus. A trait of Bistahieversor is the tall sagittal crest, perhaps an anchor point for the muscles: in the model the thickness of the neck seems to be based on Hartman’s reconstruction, however if we look at Bistahieversor’s neck in others restorations, the thickness of the neck would not be sufficient to contain the sagittal crest, let alone the tissues it was hidden beneath. Perhaps it was decided this way not to excessively hinder the neck movability. Bistahieversor has a total of 64 teeth, which apparently have the traditional knife-shape of most theropods, rather than the D-section typical of Tyrannosauridae. Of course, it’s too small a detail to be seen in the BOTM model. Recently, Carr et al. (2017) proposed some complex facial ornamentation for at least some Tyrannosauridae. The model does not follow this research, and the snout shows the same type of scales of the rest of the body.

Compared to the Series 1 Yutyrannus, Bistahieversor has some improvements in the joints: the neck has better vertical flexibility, also thanks to the new “neck hood”. Thanks to this feature, the BOTM Bistahieversor can be posed in a greater range of movements, although it is still quite limited when it comes to looking down. We have to wait until Series 3 to see improvements in that regard.

There’s another improvement in the forelimb: if in Yutyrannus the hand had a ball joint, in Bistahieversor there’s a: this allows the hand to bend up to 90° with the wrist, an angle unattainable for the previous model. Otherwise, the range of motion remains the same, and Bistahieversor can assume a good variety of poses of the real animal (and several impossible ones 😀 ).

The model features a base, the same of Yutyrannus and all the other Tyrannosaurs with 3 and 4 bodies. It has the same problems we reported for Yutyrannus: when on the base, the hindlimb is not sturdy enough to allow a stable pose without the risk of bending, even when using both the non-articulated legs. This is due to the lack of a smooth surface on the base. Therefore it’s strongly unadvised to leave it standing with one leg raised for long times. One solution is to place it without its base: the non-articulated legs, when on smooth surfaces, are stable. An alternative is to use one of the articulated action figures stands that can be bought at a low price in comic books stores or online.

The coloration is based on the Australian red-bellied black snake (Pseudechis porphyriacus), and it’s undoubtedly among the most showy and aggressive of the entire Tyrannosaur Line. It’s applied quite well: the only area where there’s a sharp difference is the terminal segment of the tail, where – perhaps because it’s made of a different material to allow the tail tip to be bent with the internal wire – the red is darker. It’s a problem common to all the models I’ve seen.

In addition to the body, Bistahieversor shares the size with the BOTM Lythronax, too. But the restored skull of Lythronax is between 70 and 80 cm long, while that of Bistahieversor is 107 cm long (for context, the skull of the largest specimen of Gorgosaurus is about 103 cm long and the famous AMNH 5027 Tyrannosaurus skull is about 135 cm). If you want the model to represent the only known adult Bistahieversor specimen, the one its skull is based on, its size makes it out of scale when compared with the rest of the BOTM Tyrannosaur Series, and even more so with the Ceratopsian Series: the BOTM Pentaceratops towers over Bistahieversor in an almost sauropod-way, when it should be the other way around. A better pairing, if you want to display the BOTM Bistahieversor with a ceratopsid of the same scale, is the significantly smaller Haolonggood Pentaceratops.

These two animals are in the same scale, but they never met. Of which the Haolonggood Nasutoceratops should be grateful.

To the end, the BOTM Bistahieversor is the best available choice for this interesting animal, and with its aggressive colours it will certainly stand out in any collection.


Brusatte S.L., Norell M.A., Carr T.D., Erickson G.M., Hutchinson J.R., Balanoff A.M., Bever, G.S., Choiniere, J.N., Makovicky P.J., Xu X. (2010) Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science 329 (5998): 1481−1485.

Carr T.D., Varricchio D.J., Sedlmayr J.C., Roberts E.M., Moore J.R. (2017) A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports. 7: 44942.

Carr T.D., Williamson T.E. (2010) Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea. Journal of Vertebrate Paleontology. 30 (1): 1–16. doi:10.1080/02724630903413032. S2CID 54029279.

Voris J.T., Therrien F.; Zelenitzky D.K., Brown C.M. (2020) A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids. Cretaceous Research. 110: 104388.

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