I’m off soon for a sunny break on the beaches of Morocco, but as an Easter gift to you, my (admirable, sagely, few, beautiful) readers, here is an image of two specimens, formerly from my freezers, to consider:
Both are the right pelvis (hip bones; crocodile pelvis is a bit broken toward the bottom) and femur (thigh bones) of living archosaurs– a 27kg emu above, and a 278kg nile crocodile below. The head would be toward the right side of the picture. A tenfold difference in mass between the bird and the crocodile, and yet some of the dimensions are so similar in both of them (femur length etc.), or so vastly different in the bipedal runner vs. the quadrupedal not-so-fast-runner (much bigger pelvis for leg muscle attachments in the former).
This image says it all. It is why I study the evolution of locomotion in land animals. It is why I am so fascinated by the transition from vaguely crocodile-like early archosaurs to modern birds by way of earlier dinosaurs. Anatomy, size, mechanics, behaviour, phylogeny… the photo captures all the facets of why I am so enraptured by research in this field.
It also might evoke thoughts of what features are expected in a terrestrial vs. aquatic animal, and thoughts of how some numbskulls still think big dinosaurs lived in the water (no I will not link to the execrable story from BBC today that I am thinking of!)…
I hope you appreciate it, too. Have a freezer-burn-free holiday period, folks!
What's In John's Freezer? 
That image really does capture a lot.
One set of comparisons I think would be fun in terms of the terrestrial vs aquatic animals bit: turtle limbs. I suggest turtles because (for others reading this; John is well aware) they include walkers, aquaflyers, drag-based swimmers, and (mostly importantly here) subaqueous walkers/runners.
That *is* a great pic.
“subaqueous walkers/runners” – like all of Dinosauria, apparently!
[…] the birds company is a fellow archosaur, which reminds me of WIJF’s previous post on pelvic differences in archosaurs; here an […]
[…] and later birds are simply proportional– they got bigger, with stronger, larger attachments on the pelvis and the front of the knee (the CC/LC, if you remember from Freezermas day […]