Femur:Tibia Ratio in Marginocephalians, and Relevant Outgroups
As a follow-up to our last post on thyreophorans, here are marginocephalians (ceratopsians and pachycephalosaurs) with some of their outgroups. Moving or removing the uncertainly-placed Stenopelix has little effect on character reconstruction.
The Open Dinosaur Project 
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What sort of postcrania exist for Zuniceratops and Turanoceratops? I know the Zuni material comes from a disarticulated bonebed, so I guess any association between limbs is problematic. Too bad – because it would nicely fill the morphological gap between protoceratopsids and ceratopsids.
There’s decent Zuni material, but it’s all disarticulated and multiple individuals. It is a bummer! Same for Turanoceratops. We’ll just have to hope for some good Mongolian or Chinese material.
Is the difference in values between T. prorsus and T. horridus a real difference between taxa, or just a sampling issue?
It’s almost certainly a sampling issue – on second glance through the specimens, most of them can’t even be distinguished to species (let alone genus).
It would be interesting to see a matrix of continuous characters using these sorts of ratios run in TNT since it permits continuous characters to have 0-65 states and at least 3 decimal places. It’d be cool to see what sort of tree resulted from running this analysis. 🙂
Nick
Well, maybe now the two Triceratops species CAN be separated. That looks like a significant proportional difference that the ODP has uncovered.
Perhaps. . .I’m not sure how reliable the species assignments are, and Triceratops taxonomy is once again in a state of flux. Probably something to note in the paper, at least.
Is the range of variation between the Triceratops specimens sufficiently large enough to be considered significant? I might not be reading the graph right, but other ceratopsians appear to show large ranges of variation…
Here’s some regression analysis plots (using data current as of 10 MAR 10) and a PCA plot of the Ceratopsians with the Humerus, Radius, Femur and Tibia all present:
https://docs.google.com/fileview?id=0B0j7XZ3vPfBnMGI2MDAyMjAtZGEwNC00OWIxLTlhNDgtOTFiNDU0YmJmYzUy&hl=en
Data available here (as Allometry_plot.Rdata and PUBLIC_Allometry_plots_HISTORY.history):
https://sites.google.com/site/daviddreisigmeyer/home/files
Here’s a paper that was previously referred to (sorry I can’t remember who brought it to our attention):
Click to access 2008_1.pdf
I would have liked to have presented the ‘Studentized residual’ in the plots but I’m not a statistician and have no idea how to do that for the nonlinear regressions. I’d be grateful if someone could explain how it’s done for a model of the form y = a + b * ( x ** c )! All that I could find was how to do it for linear models.
Greetings
I really liked this type of statistics and no doubt I will be very useful for a study I am doing. But I have a question, are the measures of the femurs and tibias may be shared with us, is it possible to add the measurements of the metatarsals, too?, and that the movement is expected not only between the femur and tibia, but the length of the ball, which is sometimes very short or long depending on species.
Thanks