Some further thoughts on Patagotitan

August 10, 2017

A bunch of stuff, loosely organized by theme.

Media

First up, I need to thank Brian Switek, who invited me to comment on Patagotitan for his piece at Smithsonian. I think he did a great job on that, arguably the best of any of the first-day major media outlet pieces. And it didn’t go unnoticed – his article was referenced at both the Washington Post and NPR (and possibly other outlets, those are the two I know of right now). I don’t think my quotes got around because they’re particularly eloquent, BTW, but rather because reporters tend to like point-counterpoint, and I was apparently the most visible counterpoint. They probably would have done the same if I’d been talking complete nonsense (which, to be fair, some people may think I was).

Paleobiology vs Records

The most commonly reproduced quote of mine is this one, originally from Brian’s piece:

I think it would be more accurate to say that Argentinosaurus, Puertasaurus and Patagotitan are so similar in size that it is impossible for now to say which one was the largest.

That may seem at odds with the, “Well, actually…[pushes glasses up nose]…Argentinosaurus was still biggest” tack I’ve taken both in my post yesterday and on Facebook. So let me elaborate a little.

There is a minor, boring point, which is that when I gave Brian that quote, I’d seen the Patagotitan paper, but not the Electronic Supplementary Materials (ESM), so I knew that Patagotitan was about the same size as the other two (and had known for a while), but I hadn’t had a chance to actually run the numbers.

The much more interesting point is that the size differences between Argentinosaurus, Puertasaurus, and Patagotitan are astonishingly small. The difference between a 2.5m femur and a 2.4m one is negligible, ditto for vertebrae with centra 59cm and 60cm in diameter. OMNH 1331, the biggest centrum bit from the giant Oklahoma apatosaur, had an intact max diameter of 49cm, making it 26% larger in linear terms than the next-largest apatosaur. The centra of these giant South American titanosaurs are more than 20% bigger yet than OMNH 1331, just in linear terms. That’s crazy.

It’s also crazy that these three in particular – Argentinosaurus, Puertasaurus, and Patagotitan – are so similar in size. Dinosaur developmental programs were ‘messy’ compared to those of mammals, both in having weird timings for things like onset of reproduction, and in varying a lot among closely related taxa. Furthermore, sauropod population dynamics should have been highly skewed toward juveniles and subadults. So is the near-equality in size among Argentinosaurus, Puertasaurus, and Patagotitan just a coincidence, or does it mean that something weird was going on? There’s really no third option. I mean, even if some kind of internal (biomechanical or physiological) or external (ecological, food or predation) constraint forced those three to the same adult body size, it’s weird then that we’re finding only or at least mostly near-max-size adults. (If the available specimens of these three aren’t near-max-size, then any hypothesis that they’re forced to the same size by constraints is out the window, and we’re back to coincidence.)

BUT

With all that said, the title of “world’s largest dinosaur” is not handed out for effort expended, number of specimens collected, skeletal completeness, ontogenetic speculation, or anything other than “the dinosaur with the largest measured elements”. And that is currently Argentinosaurus. So although for any kind of paleobiological consideration we can currently consider Argentinosaurus, Puertasaurus, and Patagotitan to all be about the same size – and Alamosaurus, Paralititan, Notocolossus, and probably others I’ve forgotten should be in this conversation – anyone wanting to dethrone Argentinosaurus needs to actually show up with bigger elements.

So, if you’re interested in paleobiology, it’s fascinating and frankly kind of unnerving that so many of these giant titanosaurs were within a hand-span of each other in terms of size. Patagotitan is one more on the pile – and, as I said yesterday, exciting because it’s so complete.

But if you want to know who holds the crown, it’s still Argentinosaurus.

Humeri

In a comment on the last post, Andrea Cau made an excellent point that I am just going to copy here entire:

Even Paralititan stromeri humerus is apparently larger than Patagotitan humerus (169 cm vs 167.5 cm). I know humerus length alone is bad proxy of body size, but at least this shows that even in that bone Patagotitan is just another big titanosaur among a well known gang of titans, not a supersized one.

That made me want to start a list of the longest sauropod humeri. Here goes – if I missed anyone or put down a figure incorrectly, I’m sure you’ll let me know in the comments.

  • Giraffatitan: 213cm
  • Brachiosaurus: 203cm
  • Ruyangosaurus: 190cm (estimated from 135cm partial)
  • Turiasaurus: 179cm
  • Notocolossus: 176cm
  • Paralititan: 169cm
  • Patagotitan: 167.5cm
  • Dreadnoughtus: 160cm
  • Futlognkosaurus: 156cm

Admittedly the Patagotitan humerus is from a paratype and not from the largest individual, but that is true for some others on the list, including Giraffatitan. And we have no humeri from Argentinosaurus, Puertasaurus, and some other giants.

Dorsal Vertebrae

A couple of further thoughts on how the dorsal vertebrae of Patagotitan compare to those of Argentinosaurus. First, now that I’ve had some time to think about it, I have a hard time seeing how the dorsal polygon method used by Carballido et al. in the Patagotitan paper has any biological meaning. In their example figure, the polygon around the Puertasaurus vertebra is mostly full of bone, and the one around Patagotitan has a lot of empty space. It’s easy to imagine an alternative metric, like “area of the minimum polygon actually filled by bone”, that would lead to a different ‘winner’. But that wouldn’t mean much, either.

Something that probably does have a real and important biomechanical meaning is the surface area of the articular face of the centrum, because that’s the area of bone that has to bear the compressive load, which is directly related to the animal’s mass. The biggest Patagotitan centrum is that of MPEF-PV 3400/5, which is at least a local maximum since has smaller centra both ahead and behind. The posterior face measures 59cm wide by 42.5cm tall. Abstracted as an ellipse, which may not be perfectly accurate, those measurements give a surface area of (pi)(29.5)(21.25)=1970 cm^2. For Argentinosaurus, the largest complete centrum has a posterior face measuring 60cm wide by 47cm tall (Bonaparte and Coria 1993: p. 5), giving an elliptical surface area of (pi)(30)(23.5)=2210 cm^2. (I’d use hi-res images of the centra to measure the actual surface areas if I could, but AFAIK those images either don’t exist or at least have not yet been made public, for either taxon.) So although the Argentinosaurus dorsal seems like it is only a bit bigger in linear terms, it’s 12% larger in surface area, and that might actually be a meaningful difference.

Cervical Vertebrae

One thing I haven’t commented on yet – Patagotitan is the newest member of the “world’s longest vertebrae” club. The longest Patagotitan cervical, MPEF-PV 3400/3, is listed in the ESM as having a centrum length of 120cm, but it’s also listed as incomplete. In the skeletal recon in the paper, the centrum is colored in as present, but the neural spine is missing. So is the centrum complete in terms of length? I don’t think it’s clear right now.

Anyway, here’s the current rundown of the longest cervical centra of sauropods (and therefore, the longest vertebrae among animals):

  • BYU 9024, possibly referable to Supersaurus or Barosaurus: 137cm
  • Price River 2 titanosauriform: 129cm
  • OMNH 53062, Sauroposeidon holotype: 125cm
  • KLR1508-77-2, Ruyangosaurus giganteus referred specimen: 124cm
  • MPEF-PV 3400/3, Patagotitan holotype: 120cm (+?)
  • MPM 10002, Puertasaurus holotype: 118cm

You may be surprised to see the Price River 2 cervical in there. It was reported in an SVP abstract a few years ago (I’ll dig up that ref and update this post), and Mike and I saw it last year on the Sauropocalypse. We measured the centrum at 129cm, making it just a bit longer than the longest centrum of Sauroposeidon, and therefore the second-longest vertebra of anything ever.

Aside – I’m probably getting a reputation as a big ole meanie when it comes to debunking “world’s largest dinosaur” claims. If I’m willing to take the lead in kicking my own dinosaur down the ladder, don’t expect me to be kind to yours. I follow where the numbers lead.

Now, here’s an interesting thing – now that Sauroposeidon is coming out as a basal titanosaur, rather than a brachiosaur, it might not have been a skinny freak. The 120cm cervical of Patagotitan makes the 125cm cervical of Sauroposeidon and the 129cm cervical from Price River 2 look even more tantalizing. Maybe it’s super-giant sauropods all the way down.

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11 Responses to “Some further thoughts on Patagotitan

  1. HikaruAmano Says:

    @ Dr. Wedel:

    What could have been the primary driver among the factors you have mentioned that led to the rise of those megasauropods? And given that Patagotitan and Argentinosaurus are sister taxa (at least in the article of Carballido et al., 2017), doesn’t that possibly indicate that Patagotitan evolved into Argentinosaurus (given that the former’s remains are found in slightly older rock horizons than the latter).

  2. Vishal Boompally Says:

    Interesting. I’ve never heard of the Prince River 2 Titanosauriform. Do we know where in the cervical series its placed in (ex. Is it a C7 or C9 or C5, etc.)?

  3. Mike Taylor Says:

    We don’t know, I’m afraid. The PR2 cervical is poorly preserved and in a dreadful state.

  4. Andrew Stuck Says:

    I thought Sauroposeidon was sexier as a brachiosaur, but I suppose we must not let awesomebro-ism blind us to the science… That’s where these silly “mine is bigger than yours!” arguments come from, anyway.

  5. Shahen Says:

    Longest cervicals reffered to Ruyangosaurus are more than 120 cm long, longest – 124 cm.

    Osteology of the giant sauropod dinosaur Ruyangosaurus giganteus Lü et al., 2014

  6. ijreid Says:

    I can confirm that Shahen is correct, I have a copy of the osteology paper, shared with me by a friend who received it from Phil Mannion.

    Ruyangosaurus would be an absolute giant as reconstructed by Lü et al 2014, but they gave it an extremely high cervical count (19 or 20 if my memory serves). Issues have been brought up in my circles that the referred material doesn’t match the holotypes much (femoral and dorsal overlap) but this is as yet speculation, and doesn’t mean that the material wasn’t from a huge giant.

  7. Shahen Says:

    In paper is information about some cervicals 120+ cm, sacrum 147 cm, humerus 190 cm!, Largest dorsal with centrum 61 cm, sacral with centrum 68 cm, etc. Mike and Matt please check email
    Best Regards

  8. Matt Wedel Says:

    Hikaru – good questions. All of the factors that make sauropods ‘work’, at least in the Sander et al. (2010) model, work progressively better at larger size. To me, that’s enough to explain why super-giant sauropods evolved. What I’m more curious about is what factors kept all the other sauropods from evolving to super-giant sizes. Or maybe most sauropods did, and we just haven’t found the giant, fully mature individuals yet.

    Vishal – as far as I know, the 129-cm centrum is the only element from a super-giant titanosauriform from that quarry. I’ve seen the rest of the material, and none of it struck me as being in a size class larger than, say, the B. altithorax holotype. Mike, do you remember anything differently?

    Shahen and ijreid – thank you for the very good catch on Ruyangosaurus, I will update the post accordingly!

  9. Shahen Says:

    There is my small analyze about biggest Dinosaurs. Also i belive that Puertasaurus was bigger than Argentinosaurus. They centra are the same wide, but Puertasaurus diapophyses are huge. Some people said that Argentinosaurus had much longer torso, but in Lognkosauria second dorsal is smaller than rest. For example first dorsal Futalognkosaurus is 43 cm and second only 2/3 that length, in Patagotitan the same. I belive that Puertasaurus 1st dorsal was around 44 cm.
    I send also file
    https://www.sendspace.com/file/1in7kr

    What do you think about this?

  10. Matt Wedel Says:

    The position of the Puertasaurus dorsal is a guess. It might be a good guess, it might not be. Given how variable vertebral form is even among titanosaurs, I would not hang a lot of importance on it definitely being D2, rather than D1 or D3. I am also not overly moved by the wide transverse processes. Maaaaybe that means that the torso was wider – certainly some people have been happy to assume that – but maybe it just means that the ribs hung down more vertically. Until we have more material, we need to keep these uncertainties at the forefront of our interpretations.


  11. […] 2014 but was formally named and published by José Carballido and colleagues just three weeks ago. While not technically the biggest known sauropod, Patagotitan is the only dinosaur in its class known  from reasonably complete remains. The […]


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