Mid-December Update

We’re long overdue for an update post. Many of our regular contributors, and a few new ones, have kept the data rolling in. Now, we’ve got over 1,400 verified entries! Thank you to everyone who has helped out with this effort. We’ve got another month and a half of data collection (according to the current schedule), so it’s not too late to get in on the action.

I’d like to give special recognition to ODP contributor Rob Taylor, who has done some fantastic work in cross-checking bibliographic entries with the various verification and public data lists. It’s a tedious task, but very important for ensuring that we have the best database possible. Thank you, Rob!

Finally, let’s do a little data exploration. Although stegosaurs have a rather crummy fossil record when it comes to delicate bits like hands and feet (or at least a crummy publication record), for some reason their ontogenetic series are crazy good. And, people who work on ontogeny of stegosaurs actually publish raw measurements! This means we can do some pretty cool meta-analyses of their data.

Femur Length vs. Tibia Length in Stegosaurus

I pulled out all of the data that are referable to Stegosaurus (or plausibly referable to Stegosaurus), and found specimens with humerus, ulna, femur, and tibia measurements. The specimens range from the really big (femur length 1,300 mm) to the rather small (femur length ~300 mm). At right is a log plot showing hind limb proportions for those individuals with both femora and tibiae preserved. We can make a comparable plot for humerus vs. ulna (not shown), and also run regressions on the data.

Interestingly, femur length and tibia length scale isometrically–their proportions are similar, regardless of body size (RMA slope=1.0057, 95 percent confidence interval 0.9049 – 1.07, N=15). By contrast, the ulna scales with positive allometry relative to the humerus–it gets relatively longer as body size increases (RMA slope=1.16, 95 percent confidence interval 1.087 – 1.317, N=15). Perhaps this is due to the olecranon process being bigger in bigger animals? We can’t really tell from the data. Finally, it looks like the humerus scales with negative allometry relative to the femur, although the confidence interval just barely includes isometry (RMA slope=0.964, 95 percent confidence interval 0.9081 – 1.004, N=14). [Note: If you’re not familiar with terms like allometry and isometry, check out this post for an explanation. And, all of the slopes presented above are for log-transformed data] It would be lots of fun to compare the stegosaur data with other ornithischians, but unfortunately the published data are just too sparse right now.

Stegosaurus, from Marsh's 1896 Dinosaurs of North America

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