SO close
August 21, 2014
I have often argued that given their long hindlimbs, massive tail-bases, and posteriorly-located centers of mass, diplodocids were basically bipeds whose forelimbs happened to reach the ground. I decided to see what that might look like.
Okay, now obviously I know that there are no trackways showing sauropods actually getting around like this. It’s just a thought experiment. But given how close the center of mass of Diplodocus is to the acetabulum, I’ll bet that this pose was achievable in life. If diplodocids had just pushed the CM a few cm farther back, they might have dispensed with forelimbs entirely, or done something different with them, like re-evolved grasping hands.
Image modified from Gilmore (1932: plate 6). Here’s a horizontal-necked bipedal Diplodocus and the original pose:
UPDATE the next day: I had forgotten that Niroot had already done a bipedal Apatosaurus, and a much more convincing one than mine. Go see it.
UPDATE the next week: Well, heck. Looks like the primary value of this post was so that people would remind me of all the other places the same idea has already been covered better. As you can see from the comment thread, Mike blogged about this at the WWD site, Scott Hartman drew it, and Heinrich Mallison showed that it was plausible. Sheesh, I suck.
Reference
- Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81, 1-21.
Sauropod Vertebra Picture of the Week 
August 21, 2014 at 2:22 am
Actually, we’re discussing adult bipedal walking in the book, and definitely young juveniles.
August 21, 2014 at 2:55 am
CMs?! I didn’t realize it was that close. Quite incredible!
August 21, 2014 at 2:56 am
I guess we’ll just have to wait for the discovery of that Late Cretaceous sauropod with grasping hands, huh?
August 21, 2014 at 4:38 am
Very cool. The only issue I have is that any bipedal animal has to bear all of its weight on one limb or the other if it’s to walk around. There must be an upper limit for mass and I wonder if even comparatively slender Diplodocus might exceed that?
I imagine that if bipedal sauropods were going to happen, it would have needed to be after plant material with higher energy densities became available such as with the rise of angiosperms, so that those sauropods could reduce their reliance on having to have massive fermentation vats to extract as much of the nutrition as possible.
Perhaps therizinosaurs effectively filled this niche?
August 21, 2014 at 6:20 am
Very cool. The only issue I have is that any bipedal animal has to bear all of its weight on one limb or the other if it’s to walk around. There must be an upper limit for mass and I wonder if even comparatively slender Diplodocus might exceed that?
I doubt it. For one thing, the common reference specimens of Diplodocus (CM 84/94, USNM 10865) probably did not exceed 15 metric tons and may have been as light as 10. The heaviest sauropods probably got up around 100 tons. Even assuming they kept three feet on the ground, that’s 30+ tons per limb, or roughly double what a bipedal Diplodocus would require on each limb.
There’s also this.
Perhaps therizinosaurs effectively filled this niche?
I think you nailed it. Therizinosaurs, Gigantoraptor, and Deinocheirus. That’s partly why this possibility of bipedal sauropods is so interesting to me. As the post title implies, it seems like sauropods were *this* close to inventing that body form a few tens of millions of years early.
August 21, 2014 at 7:51 am
Wings, *obviously*.
August 21, 2014 at 8:02 am
I think you could make this look more convincing by using a more modern Diplodocus skeleton that doesn’t have that early-20C downward curve in the anterior part of the torso. See for example Scott Hartman’s version.
August 21, 2014 at 12:07 pm
If you’ll forgive the intrusion, I had a go at drawing a bipedal Apatosaurus once, inspired by Mike’s article on the Walking with Dinosaurs blog and Scott Hartman’s skeletal.
August 22, 2014 at 2:31 am
Thanks Matt. I should’ve done the per limb calc myself and answered my own Q. I also thought of both Gigantoraptor and Deinocheirus as possibly being the last bricks in that wall to keep the sauropods firmly on all fours.
And thanks for the link to the abstract of you paper. Did you not consider the material sufficiently diagnostic to name a new species?
August 22, 2014 at 6:18 am
Wasn’t Spinosaurus in the mass range of the (non-hallorum) Diplodocus also?
I wonder if Supersaurus and Diplodocus hallorum had more balanced weight distribution?
August 22, 2014 at 7:30 am
Did you not consider the material sufficiently diagnostic to name a new species?
Ah, that project. Opposite problem, actually: there turned out to be more material than we originally thought. But we discovered that right about the time that Adam Yates moved from South Africa back to his native Australia. Now the two authors and the fossils are all on different continents. So although we do still plan to get this thing properly written up, you’ll probably see Avengers 3 before the paper is done and out.
Wasn’t Spinosaurus in the mass range of the (non-hallorum) Diplodocus also?
Certainly possible.
I wonder if Supersaurus and Diplodocus hallorum had more balanced weight distribution?
I dunno. So far everything I’ve seen makes me think they’re basically just scaled up without any major body plan changes. Scott Harman would know, if anyone does.
August 22, 2014 at 2:45 pm
…you’ll probably see Avengers 3 before the paper is done and out.
That is disconcerting for more than one reason.
August 23, 2014 at 2:18 am
10-ton prosauropods languishing in obscurity… So sad.
August 24, 2014 at 2:37 am
Thanks for the mention Mike, and of course I did this for your article last year: http://www.walkingwithdinosaurs.com/suploads/bipedal-apatosaurus-hartman_medium.jpg
August 24, 2014 at 4:10 am
Anyone here heard of Dreadnoughtus schrani yet! Looks pretty awesome!
August 24, 2014 at 11:29 pm
[…] Thus, Mike had to go ahead and publish the planned blog post without my figure. Here’s the link. […]
August 25, 2014 at 12:21 am
Seeing as no-one else has said it yet, I will… pangolins.
August 27, 2014 at 8:26 am
For anyone who doesn’t know what Darren is alluding to: https://www.youtube.com/watch?v=gz4HXyxcess
September 5, 2014 at 8:56 am
Nice to see that others have suggested this. In 2006, I made a series of dinosaur pictures for an exhibition, including a bipedal Amargasaurus… Unfortunately, that sauropod was rejected by the commitee as “not plausible”, and I was asked to re-draw it in quadrupedal posture… :-(
September 26, 2014 at 9:27 am
it’s interesting how high Gilmore projected the tail, despite still feeling the need to drag it. also, the length of this tail may be related to temporary bipedism, don’t you think so?
March 6, 2015 at 11:23 am
[…] I don’t even remember drawing this, I just found it lying around and spruced it up a bit today. It’s supposed to be some kinda diplodocid, maybe Kaatedocus, but I think the main goal of the drawing was to draw one with a sense of weight that felt right given that their center of mass is supposed to be so far back. I like the idea of them getting startled and popping up every now and again… [see also–MJW] […]