The humerus of Brachiosaurus altithorax, part 1: the fossil
May 20, 2014
In the comments on Matt’s post about the giant new Argentine titanosaur specimens, Ian Corfe wondered why Benson et al. (2014) estimated the circumference of the humerus of Brachiosaurus altithorax instead of just measuring it. (Aside: I can’t find that data in their paper. Where is it?)
Yes, the humerus is half-encased in a jacket, face down (we should post photos some time), which would make the circumference impossible to measure directly. But the mounted Brachiosaurus skeleton right outside the Field Museum (and the identical one at O’Hare Airport) have casts of that humerus, so measuring the circumference shouldn’t require any equipment more exotic than a stepladder. Maybe the anterior aspect was sculpted — but I doubt it, as there certainly was a time when the humerus was out of its jacket and mounted vertically.
Here is the evidence that the humerus wasn’t always in that jacket (from Getty Images):
I have no idea why it was put back in a plaster jacket: does anyone?
Back in 2005, when Matt and I visited the Field Museum, the staff were amazingly, almost embarrassingly, helpful. They mounted a whole elaborate project to remove the humerus jacket from the cabinet that held it, so we could get a better look:
Unfortunately, Matt and I were doofuses back in the day: terrible photographers who knew embarrassingly little about appendicular material. So nearly all of our photos are worthless. Here is a rare nice one, showing the humerus in posterodistal aspect. You can see how layers have flaked away towards this end:
Here is the humerus in proximal view — something that’s relevant to my interests, as at tells us about the area of articular cartilage where it connected to the shoulder:
And finally — because it would be rude not to — here is Matt, going the Full Jensen with the humerus:
Next time: what we can learn about the humerus from the mounted skeleton outside the museum!
Benson Roger B. J., Nicolás E. Campione, Matthew T. Carrano, Philip D. Mannion, Corwin Sullivan, Paul Upchurch, and David C. Evans. (2014) Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology 12(5):e1001853. doi:10.1371/journal.pbio.1001853