The Brachiosaurus altithorax holotype FMNH PR 25107 in the ground

Wednesday, May 1, 2024 18:22

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I was cleaning out my Downloads directory — which, even after my initial forays, still accounts for 11 Gb that I really need to reclaim from my perptually almost-full SSD. And I found this beautiful image under the filename csgeo4028.jpeg.

Brachiosaurus altithorax holotype FMNH PR 25107 during excavation.

The thing is, I have no idea where this image came from. The file’s timestamp says it’s been 16 months since I downloaded it from somewhere, but there is no associated metadata that tells me where I got it. Googling for the filename gets me nothing.

Can anyone find the source?

Anyway, I immediately recognised it as our old friend Brachiosaurus altithorax, and in fact it’s a much better version of a photo that we’ve featured here before, That version was scanned from Supplement 1 of Don Glut’s encyclopedia, which credits it as being Field Museum neg. #4027 (which is one out from the number in the filename). But that doesn’t explain where this high-resolution copy came from.

Anyway, looking at this image in 2024, I’m immediately interested in the ribs, which of course Matt and I published on at the very end of 2023 (Taylor and Wedel 2023, natch). It shows both ribs A and B in their original state, and it’s instructive to compare them with those ribs as we illustrated them in our paper.

First, rib A:

Taylor and Wedel 2023:Figure 2. Sauropod dinosaur Brachiosaurus altithorax Riggs, 1903, holotype FMNH PR 25107 from Dinosaur Quarry No. 13 near Grand Junction, Colorado, dating to the Kimmeridgian–Tithonian ages of the Late Jurassic, right dorsal rib “Rib A” in posterior view with proximal to the left. A1, the whole proximal half of the rib; a distal portion also exists, of similar length but without features relevant to this study; A2, close-up of the tuberculum, highlighting the complex network of support structures that show signs of speculative reconstruction. Circles highlight two possible sites of the “second tubercle” referred to by Riggs (1901: 549, 1903: 303, 1904: 239) based on Marsh’s illustration (1896: figs. 7, 8), reproduced here in Fig. 4; A3, close-up of the pneumatic foramen in the shaft of the rib, showing natural bone texture around the margin and no indication of breakage. Scale bars provide only a rough indication of the size of the elements: see the text for measurements.

This one is visible at the bottom of the photo, proximal end to the bottom, but flipped over from the way it now rests in the collection, so the pneumatic opening is not apparent. There’s an interesting “folded over” ridge running down the anterior(*) face of the proximal part of the shaft.

(*) Assuming we were right in interpreting the available face of the rib as posterior in our paper.

Now, Rib B:

Taylor and Wedel 2023:Figure. 3. Sauropod dinosaur Brachiosaurus altithorax Riggs, 1903, holotype FMNH PR 25107 from Dinosaur Quarry No. 13 near Grand Junction, Colorado, dating to the Kimmeridgian–Tithonian ages of the Late Jurassic, left dorsal rib “Rib B”. A1, the whole rib, posterior face in proximal view. Foreshortening makes the shaft look shorter and narrower than it actually is: the position of the rib between two shelves makes it impossible to photograph in true posterior view; A2, close-up of the pneumatic opening in the tuberculum in medial view, with anterior to the bottom; A3, red-cyan anaglyph of the same, indicating the form and depth of the fossa. Scale bars provide only a rough indication of the size of the elements: see the text for measurements.

This is visible on the left side of the image, close to the vertebral column, with the proximal end to the top. It has the same (posterior, we think) face upwards as is available in the collection, and you can make out the pneumatic opening in the tuberculum that we illustrated.

Reference