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DrScottHartman — A real deceptive reptile
Published: 2013-05-10 16:48:40 +0000 UTC; Views: 14186; Favourites: 147; Downloads: 0
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Description
Apatosaurus ajax is the type species of Apatosaurus ("deceptive reptile"), so if someone ever manages to resurrect Brontosaurus (which is tied to A. excelsus), this animal won't be changing its name. The skeletal is a long-needed revision to the skeletal I did for a paper I and colleagues published on Supersaurus back in 2007 (we subsequently dropped it from the final paper).The reconstruction is based on NSMT-PV 20375, a specimen on display in Tokyo (thankfully I had the opportunity to made a couple trips to see it). Like the type specimen it's not full grown, and it's probable that the animal would have "grown into" its fairly long limbs as it got larger. How much larger? Possibly quit a bit larger, as most of the largest reported specimens have been at least tentatively referred to A. ajax, although it's hard to be certain without proper descriptions.
Despite this, it seems evident that A. ajax wasn't as robust as A. excelsus, and it wasn't close to being the overbuilt steroid-user that A. louisae was [link]
Interestingly it also seems to retain the smaller pelvis and found in Supersaurus [link] although whether this has any phylogenetic value isn't clear.
Either way, this is the species that should actually be driving our understanding of Apatosaurus, and that makes it pretty darned interesting in my book.
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Comments: 76
I expect to have pics/links to show you soon. For now, see what you think of this...[link] In other words, you are invitred!
As for how much muscle can fit on bones. Hmmmmm. Look up Ronald Coleman. Buy a chicken leg at a grocery store and dissect it. Buy the leg quarter, where you can see some of the pelvic structure. Yes, I am referring to the front legs for the most part. I have a great deal of respect for your artistic ability and your knowledge, otherwise I would not even mention anything to you. I like to learn too!
And if, as has been claimed, a scientist says sauropods scarcely needed to do more than walk slowly, I get skeptical.
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Right, but human body builders achieve a truly unnatural level of mass, they consume an unreasonable amount of calories (to sustain said mass) and they more prone to suffering injuries (join injuries are particularly common in heavily muscled athletes). They are useless as a comparison for reconstructing normal, healthy animals.
As for chickens, I've dissected them (and there are published dissections as well, and you can always look at naked ones: [link] ), and the thighs are...just as long as the ilium. As you would expect, and as they are in most modern dinosaur reconstructions.
It's true that chickens have very plump thighs as seen in side view (and very large ilia to support them), but modern birds in general have expanded their thighs as they lost the important tail-based leg muscles and transitioned to a knee-driven form of locomotion. Also, the guts of birds tend to be much broader, so those thighs aren't nearly as deep as they are wide: [link]
In particular birds have also had to trade off some of the internal pelvic muscles that originated on the pubis and ischium and shift some of that function to the thighs. And finally (of course), chickens have been selected by humans to pack on as much breast and leg muscle as possible, because they're a better market value (and they also get their feed for free).
Ostriches (which are larger but have to forage in the wild) don't have such over-proportioned thigh and calve muscles as chickens: [link] [link]
You are certainly right to be skeptical of anyone who tells you that all a sauropod had to do was saunter it's whole life, but the point is that elephants are amazingly capable animals (including hand stands, rearing, killing rhinos, and speeds faster than I can maintain these days) with skinny limb muscles. As I've said more than once I agree that sauropods had better developed limb muscles than elephants in some areas, but elephants show you can be active at a large size with less muscle than you are presuming.
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And they are delicious! The chickens, I mean. Thanks for the links to the pics! The birds you showed are actually more heavily muscled than I thought. I'll find some links soon to show you what I mean. The Coleman example was just meant to show how much muscle can be packed on seemingly little bone. No, he's not natural. Stay tuned!
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Great work - as always!
Just a question:
Does your schedule leave the possibility to create a Kaatedocus siberi skeletal drawing?
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Not in the near term I'm afraid, although I'd love to do both Kaatedocus and Suuwassea.
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I'd imagine an adult ~30-35 meter Apatosaurus would be a serious bruiser! So, are the giant OMNH apatosaurs thought to belong to any species, or are they too fragmentary to tell? I'd guess they weigh roughly 45-60 tons, depending on which species you use to scale them up.
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The OMNH has them labeled as A. ajax, but I don't know how they determined that. I believe the size was estimated at 93 feet and 40 tons.
Of course, if it was actually excelsus or louisae, 45+ is definitely closer.
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That sounds about right to me. You definitely wouldn't want it to step on your toe!
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Brachiosaurus's grasp on "heaviest Morrison Sauropod" is looking a bit tenuous!
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Not very likely, as there aren't and published adult specimens that are complete enough.
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Maybe it seems a little bet perfect for their cousins of the Jurassic.
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Wow, that is a very noticeable difference between A. ajax and A. louisae! I hadn't realized that before.
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Yes, but the only one visible in side view is the far manus (it's there if you look closely).
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Are there any theories or hypotheses explaining that trio of huge hindlimb claws? Or are they merely a remnant with no particular need to "de-evolve"?
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They are larger than the primitive condition, so they must have evolved to do something. I suppose they may have helped keep theropods away from the otherwise vulnerable sides (although even a clawless kick would have been life-threatened). Perhaps they could help provide traction on certain substrates? Honestly I think it's still up in the air right now.
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Ahem! The hind foot claws are shaped like bananas. The reason is so that IF they see a banana, they can say: "See that yeller fruit? Is shaped like my hind foot claws!" 
Actually, Scott, I like your idea better.
But mine is funnier...
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I remember an article about titanosaur nests that showed the probable method used to make them was gouging a trough on the ground with one of their hindlimbs. Considering that large size evolved rather early in sauropods it's likely diplodocids did something similar. Larger claws would sure help in that regard.
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Yup, digging nests would certainly fall into the realm of uses for enlarged toe claws. But is it the main reason? I might expect sexual dimorphism if nest digging was the main function.
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Well then, there's an avenue of research 
Also I'd say developments regarding reproduction are pretty damn important
I've heard the improved traction hypothesis before, namely to conquer steep river embankments in that iteration. The thing is the comparable animals, large mammals, do pretty good without enlarged claws.
Did the Morrison Fm geomorphology had a marked relief around rivers (thinking of Masai Mara and fording wildebeest)?
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It's worth noting that not all sauropods have the same sized toe claws, so it would seem like reduction should be possible, although you're right that it isn't always possible for characters to evolve independently between genders.
As for the traction hypothesis, while I'm hardly married to it this may be an area where direct comparisons to large mammals isn't warranted, since mammals are forelimb dominated and large dinosaurs are hind-leg dominated. It's thus at least plausible that their traction needs differ.
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