The Dry Mesa Brachiosaur

Unnamed genus and species - Jensen's "Ultrasauros", well, the part which led it to fame in the first place. And no, it's most likely not a Brachiosaurus.


Temporal range: Late Jurassic, Kimmeridgian, around ~153 Ma

Probable length: Around ~15-20 metres?
Probable mass: Around ~15 tonnes?


The Dry Mesa Brachiosaur (BYU 9462) is a currently-unnamed brachiosaur taxon known from a large shoulder girdle, or scapulacoracoid, measuring about ~2.5 metres long in total length.

It was once composited with other remains from the same locality, some of which are now attributed to the giant diplodocoid Supersaurus vivanae, to form a giant brachiosaur, named Ultrasaurus macintoshi (meaning "Macintosh's ultra reptile") estimated to reach about ~25-30 metres in length and ~8 metres high at the shoulder, which would have massed over 70 tonnes. At that time, estimates reached up to ~180 tonnes, placing it on the same general tier as estimates for fragmentary gigapods such as Amphicoelias fragillimus.

However, this giant chimera fell apart when it was found that many of the bones it was comprised of were from Supersaurus. Since the holotype for Jensen's Ultrasauros macintoshi was one of the Supersaurus bones (a neck vertebra, BYU 5000) rather than the scapulacoracoid, Ultrasauros became a junior synonym of Supersaurus vivanae, leaving the scapulacoracoid belonging to an unnamed taxon.

Although many palaeontologists, including Greg Paul, suggested that it was just a Brachiosaurus altithorax specimen, critical differences emerged - the coracoids of B. altithorax and Jensen's Dry Mesa brachiosaur are quite different in shape. In addition, the fusion of the scapula and coracoid on the Dry Mesa Brachiosaur suggested an adult animal, but based on comparison of the coracoid width with the Brachiosaurus altithorax holotype, which was a subadult animal, the Dry Mesa Brachiosaur looks to be a much smaller - in fact, based on comparisons of coracoid width between it and the B. altithorax holotype, the Dry Mesa Brachiosaur can be estimated at roughly around ~16 metres in axial length, a long shot from the apocryphal ~30-metre brachiosaur of Jensen's fame.

In 2009, sauropod specialist Mike Taylor was the first to point out that this was most likely a separate taxon altogether. The large length of the scapula, combined with the relatively diminutive coracoid probably suggested, proportionally, a considerably deeper chest, higher shoulders, and a steeper slope on the back than Brachiosaurus.
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Done as a request by . The request called for an "Ultrasauros" brachiosaurid, and since the 1980s concept was basically just an upscaled Brachiosaurus altithorax, I decided to go for something a bit more, well, different-looking, and actually tried to reconstruct Jensen's Dry Mesa Brachiosaur instead. I filled in the rest of the body based on 's Brachiosaurus.
And you can take a good guess on what the colouration is based on.