What allowed sauropods to get big, and what kept them from getting any bigger?

January 12, 2018

This post started out as a comment on this thread, kicked off by Dale McInnes, in which Mike Habib got into a discussion with Mike Taylor about the max size of sauropods. Stand by for some arm-waving. All the photos of outdoor models were taken at Dino-Park Münchehagen back in late 2008.

I think it’s all too easy to confuse how big things do get from how big they could get, assuming different selection pressures and ecological opportunities. I’m sure someone could write a very compelling paper about how elephants are as big as they could possibly be, or Komodo dragons, if we didn’t have indricotheres and Megalania to show that the upper limit is elsewhere. This is basically what Economos (1981) did for indricotheres, either forgetting about sauropods or assuming they were all aquatic.

Truly, a mammal of excellence and distinction. With Mike and some dumb rhino for scale.

In fact, I’ll go further: a lot of pop discussions of sauropod size assume that sauropods got big because of external factors (oxygen levels, etc.) but were ultimately limited by internal factors, like bone and cartilage strength or cardiovascular issues. I think the opposite is more likely: sauropods got big because of a happy, never-repeated confluence of internal factors (the Sander/et al. [2008, 2011, 2013] hypothesis, which I think is extremely robust), and their size was limited by external, ecological factors.

Take a full-size Argentinosaurus or Bruhathkayosaurus – even modest estimates put them at around 10x the mass of the largest contemporary predators. Full-grown adults were probably truly predator-immune, barring disease or senescence. So any resources devoted to pushing the size disparity higher, instead of invested in making more eggs, would basically be wasted.

If there was reproductive competition among the super-giants, could the 100-tonners have been out-reproduced by the 70-tonners, which put those extra 30 tonnes into making babies? Or would the 100-tonners make so many more eggs than the 70-tonners (over some span of years) that they’d still come out on top? I admit, I don’t know enough reproductive biology to answer that. (If you do, speak up in the comments!) But if – if – 70-tonners could out-reproduce 100-tonners, that by itself might have been enough to put a cap on the size of the largest sauropods.

Another possibility is that max-size adult sauropods were neither common nor the target of selection. In most populations most of the time, the largest individuals might have been reproductively active but skeletally-immature and still-growing subadults (keep in mind that category would encompass most mounted sauropod skeletons, including the mounted brachiosaurs in Chicago and Berlin). If such individuals were the primary targets of selection, and they were selected for a balance of reproductive output and growth, then the few max-size adults might represent the relatively rare instances in which the developmental program “overshot” the selection target.

Dave Hone and Andy Farke and I mentioned this briefly in our 2016 paper, and it’s come up here on the blog several times before, but I still have a hard time wrapping my head around what that would mean. Maybe the max-size adults don’t represent the selective optimum, but rather beneficial traits carried to extreme ends by runaway development. It seems at least conceivable that the bodies of such animals might have been heavily loaded with morphological excrescences – like 15- to 17-meter necks – that were well past the selective optimum. As long as those features weren’t inherently fatal, they could possibly have been pretty darned inefficient, riding around on big predator-immune platforms that could walk for hundreds of kilometers and survive on garbage.

What does that swerve into weird-but-by-now-well-trod ground have to do with the limits on sauropod size? This: if max-size adults were not heavy selection targets, either because the focus of selection was on younger, reproductively-active subadults, or because they’d gotten so big that the only selection pressure that could really affect them was a continent-wide famine – or both – then they might not have gotten as big as they could have (i.e., never hit any internally-imposed, anatomical or biomechanical limits) because nothing external was pushing them to get any bigger than they already were.

Or maybe that’s just a big pile of arm-wavy BS. Let’s try tearing it down, and find out. The comment thread is open.

References

Posted by Matt Wedel
Filed in brachiosaurids, diplodocids, Giraffatitan, life restorations, size, stinkin' mammals, stinkin' SV-POW!sketeers, travel
52 Comments »

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.

Posted by Matt Wedel
Filed in Alamosaurus, Argentinosaurus, cervical, dorsal, Notocolossus, Paralititan, Patagotitan, Puertasaurus, Sauroposeidon, size, titanosaur
22 Comments »

Don’t believe the hype: Patagotitan was not bigger than Argentinosaurus

August 9, 2017

“But wait, Matt”, I hear you thinking. “Every news agency in the world is tripping over themselves declaring Patagotitan the biggest dinosaur of all time. Why are you going in the other direction?”

Because I’ve been through this a few times now. But mostly because I can friggin’ read.

Maximum dorsal centrum diameter in Argentinosaurus is 60cm (specimen MCF-PVPH-1, Bonaparte and Coria 1993). In Puertasaurus it is also 60cm (MPM 10002, Novas et al. 2005). In Patagotitan it is 59cm (MPEF-PV 3400/5, Carballido et al. 2017). (For more big centra, see this post.)

Femoral midshaft circumference is 118cm in an incomplete femur of Argentinosaurus estimated to be 2.5m long when complete (Mazzetta et al. 2004). A smaller Argentinosaurus femur is 2.25m long with a circumference of 111.4cm (Benson et al. 2014). The largest reported femur of Patagotitan, MPEF-PV 3399/44, is 2.38m long and has a circumference of either 101cm (as reported in the Electronic Supplementary Materials to Carballido et al 2017) or 110cm (as reported in the media in 2014*).

TL;DR: 60>59, and 118>111>110>101, and in both cases Argentinosaurus > Patagotitan, at least a little bit.

Now, Carballido et al (2017) estimated that Patagotitan was sliiiiightly more massive than Argentinosaurus and Puertasaurus by doing a sort of 2D minimum convex hull dorsal vertebra area thingy, which the Patagotitan vertebra “wins” because it has a taller neural spine than either Argentinosaurus or Puertasaurus, and slightly wider transverse processes than Argentinosaurus (138cm vs 128cm) – but way narrower transverse processes than Puertasaurus (138cm vs 168cm). But vertebrae with taller or wider sticky-out bits do not a more massive dinosaur make, otherwise Rebbachisaurus would outweigh Giraffatitan.

Now, in truth, it’s basically a three-way tie between Argentinosaurus, Puertasaurus, and Patagotitan. Given how little we have of the first two, and how large the error bars are on any legit size comparison, there is no real way to tell which of them was the longest or the most massive. Still, to get to the conclusion that Patagotitan was in any sense larger than Argentinosaurus you have to physically drag yourself over the following jaggedly awkward facts:

  1. The weight-bearing parts of the anterior dorsal vertebrae are larger in diameter in both Argentinosaurus and Puertasaurus than in Patagotitan. Very slightly, but still, Patagotitan is the smallest of the three.
  2. The femora of Argentinosaurus are fatter than those of Patagotitan, even at shorter length. The biggest femora of Argentinosaurus are longer, too.

So all of the measurements of body parts that have to do with supporting mass are still larger in Argentinosaurus than in Patagotitan.

Now, it is very cool that we now have a decent chunk of the skeleton of a super-giant titanosaur, instead of little bits and bobs. And it’s nice to know that the numbers reported in the media back in 2014 turned out to be accurate. But Patagotitan is not the “world’s largest dinosaur”. At best, it’s the third-largest contender among near equals.

Parting shot to all the science reporters who didn’t report the same numbers I did here: instead of getting hype-notized by assumption-laden estimates, how about doing an hour’s worth of research making the most obvious possible comparisons?

Almost immediate UPDATE: Okay, that parting shot wasn’t entirely fair. As far as I know, the measurements of Patagotitan were not available until the embargo lifted. Which is in itself odd – if someone claims to have the world’s largest dinosaur, but doesn’t put any measurements in the paper, doesn’t that make your antennae twitch? Either demand some measurements so you can make those obvious comparisons, or approach with extreme skepticism – especially if the “world’s largest dino” claim was pre-debunked three years ago!

* From this article in the Boston Globe:

Paleobiologist Paul Upchurch of University College London believes size estimates are more reliable when extrapolated from the circumference of bones.

He said this femur is a whopping 43.3 inches around, about the same as the Argentinosaurus’ thigh bone.

‘‘Whether or not the new animal really will be the largest sauropod we know remains to be seen,’’ said Upchurch, who was not involved in this discovery but has seen the bones first-hand.

Some prophetically appropriate caution from Paul Upchurch there, who has also lived through a few of these “biggest dinosaur ever” bubbles.

References

Posted by Matt Wedel
Filed in Argentinosaurus, Look, this isn't complicated, mass estimates, math, media FAIL, Patagotitan, size, titanosaur
48 Comments »

How horrifying was the neck of Barosaurus?

September 16, 2016

Suppose that I and Matt were right in our SVPCA talk this year, and the
“Supersaurus” cervical BYU 9024 really is the C9 of a gigantic Barosaurus. As we noted in our abstract, its total length of 1370 mm is exactly twice that of the C9 in AMNH 6341, which suggests its neck was twice as long over all — not 8.5 m but 17 m.

How horrifying is that?

I realised one good way to picture it is next to the entire mounted skeleton of Giraffatitan at the Museum für Naturkunde Berlin. That skeleton is 13.27 m tall. At 17 m, the giant barosaur neck would be 28% longer than the total height of Giraffatitan.

Giraffatitan brancai mounted skeleton MB.R.2181 at the Museum für Naturkunde Berlin, with neck of Barosaurus ?lentus BYU 9024 at the same scale. Photo by Axel Mauruszat, from Wikipedia; drawing from Scott Hartman's Supersaurus skeleton reconstruction.

Giraffatitan brancai mounted skeleton MB.R.2181 at the Museum für Naturkunde Berlin, with neck of Barosaurus ?lentus BYU 9024 at the same scale. Photo by Axel Mauruszat, from Wikipedia; drawing from Scott Hartman’s Supersaurus skeleton reconstruction.

Yes, this looks ridiculous. But it’s what the numbers tell us. Measure the skeleton’s height and the neck length off the image yourself if you don’t believe me.

(Note, too, that the size of the C9 in that big neck is about right, compared with a previous scaled image that Matt prepared, showing the “Supersaurus” vertebra in isolation alongside the Chicago Brachiosaurus.)

Posted by Mike Taylor
Filed in Barosaurus, diplodocids, Giraffatitan, Museum für Naturkunde Berlin, museums, public galleries, size, Supersaurus
118 Comments »

Giant Oklahoma Apatosaurus mount, from above

February 27, 2016

Clash of the Titans from above

Here’s the “Clash of the Titans” exhibit at the Sam Noble Oklahoma Museum of Natural History, featuring the reconstructed skeletons of the giant Oklahoma Apatosaurus – which I guess should now be called the giant Oklahoma apatosaurine until someone sorts out its phylogenetic position – and the darn-near-T. rex-sized Saurophaganax maximus, which may be Allosaurus maximus depending on who you’re reading.

Now, I love this exhibit in both concept and execution. But one thing that is more obvious in this view from the upper level balcony is that despite its impressive weaponry, a lone 3-to-5 ton Saurophaganax had an Arctic ice cap’s chance in the Anthropocene of taking down a healthy 30-meter, 40-50 ton apatosaur (which is to say, none). I like to imagine that in the photo above, the apatosaur is laughing at the pathetically tiny theropod and its delusions of grandeur.

Clash of the Titans from behind

In this shot from behind, you get a better look at the baby apatosaur standing under the big one, and it hints at a far more likely target for Saurophaganax and other large Morrison theropods: sauropods that were not fully-grown, which was almost all of them. I am hip to the fact that golden eagles kill deer, and some lions will attack elephants – as Cookie Monster says, “Sometime food, not anytime food” – but not only were smaller sauropods easier prey, they were far more numerous given the inevitable population structure of animals that started reproducing at a young age and made more eggs the bigger they got (as essentially all egg-laying animals do).

In fact, as discussed in our recent paper on dinosaur ontogeny (Hone et al. 2016), there may have been times when the number of fully-grown sauropods in a given population was zero, and the species was maintained by reproducing juveniles. The giant Oklahoma apatosaurine is a unique specimen today – by far the largest apatosaurine we have fossils of – but it may also have been an anomaly in its own time, the rare individual that made it through the survivorship gauntlet to something approaching full size.

Amazingly enough, there is evidence that even it was not fully mature, but that’s a discussion for another day. Parting shot:

Oklahoma Apatosaurus neck and head

Reference

Posted by Matt Wedel
Filed in alert sauropods not being eaten, diplodocids, Giant Oklahoma apatosaurine, juvenile, mounts, museums, OMNH, ontogeny, public galleries, Saurophaganax, size, stinkin' theropods
28 Comments »

Notocolossus is a beast

January 20, 2016

Notocolossus skeletal recon - Gonzalez Riga et al 2016 fig 1

(a) Type locality of Notocolossus (indicated by star) in southern-most Mendoza Province, Argentina. (b) Reconstructed skeleton and body silhouette in right lateral view, with preserved elements of the holotype (UNCUYO-LD 301) in light green and those of the referred specimen (UNCUYO-LD 302) in orange. Scale bar, 1 m. (González Riga et al. 2016: figure 1)

This will be all too short, but I can’t let the publication of a new giant sauropod pass unremarked. Yesterday Bernardo González Riga and colleagues published a nice, detailed paper describing Notocolossus gonzalezparejasi, “Dr. Jorge González Parejas’s southern giant”, a new titanosaur from the Late Cretaceous of Mendoza Province, Argentina (González Riga et al. 2016). The paper is open access and freely available to the world.

As you can see from the skeletal recon, there’s not a ton of material known from Notocolossus, but among giant sauropods it’s actually not bad, being better represented than Argentinosaurus, Puertasaurus, Argyrosaurus, and Paralititan. In particular, one hindfoot is complete and articulated, and a good chunk of the paper and supplementary info are devoted to describing how weird it is.

But let’s not kid ourselves – you’re not here for feet, unless it’s to ask how many feet long this monster was. So how big was Notocolossus, really?

Well, it wasn’t the world’s largest sauropod. And to their credit, no-one on the team that described it has made any such superlative claims for the animal. Instead they describe it as, “one of the largest terrestrial vertebrates ever discovered”, and that’s perfectly accurate.

Notocolossus limb bones - Gonzalez Riga et al 2016 fig 4

(a) Right humerus of the holotype (UNCUYO-LD 301) in anterior view. Proximal end of the left pubis of the holotype (UNCUYO-LD 301) in lateral (b) and proximal (c) views. Right tarsus and pes of the referred specimen (UNCUYO-LD 302) in (d) proximal (articulated, metatarsus only, dorsal [=anterior] to top), (e) dorsomedial (articulated), and (f) dorsal (disarticulated) views. Abbreviations: I–V, metatarsal/digit number; 1–2, phalanx number; ast, astragalus; cbf, coracobrachialis fossa; dpc, deltopectoral crest; hh, humeral head; ilped, iliac peduncle; of, obturator foramen; plp, proximolateral process; pmp, proximomedial process; rac, radial condyle; ulc, ulnar condyle. Scale bars, 20 cm (a–c), 10 cm (d–f). (Gonzalez Riga et al 2016: figure 4)

Any discussions of the size of Notocolossus will be driven by one of two elements: the humerus and the anterior dorsal vertebra. The humerus is 176 cm long, which is shorter than those of Giraffatitan (213 cm), Brachiosaurus (204 cm), and Turiasaurus (179 cm), but longer than those of Paralititan (169 cm), Dreadnoughtus (160 cm), and Futalognkosaurus (156 cm). Of course we don’t have a humerus for Argentinosaurus or Puertasaurus, but based on the 250-cm femur of Argentinosaurus, the humerus was probably somewhere around 200 cm. Hold that thought.

Notocolossus and Puertasaurus dorsals compared

Top row: my attempt at a symmetrical Notocolossus dorsal, made by mirroring the left half of the fossil from the next row down. Second row: photos of the Notocolossus dorsal with missing bits outlined, from Gonzalez Riga et al (2016: fig. 2). Scale bar is 20 cm (in original). Third row: the only known dorsal vertebra of Puertasaurus, scaled to about the same size as the Notocolossus vertebra, from Novas et al. (2005: fig. 2).

The anterior dorsal tells a similar story, and this is where I have to give González Riga et al. some props for publishing such detailed sets of measurements in the their supplementary information. They Measured Their Damned Dinosaur. The dorsal has a preserved height of 75 cm – it’s missing the tip of the neural spine and would have been a few cm taller in life – and by measuring the one complete transverse process and doubling it, the authors estimate that when complete it would have been 150 cm wide. That is 59 inches, almost 5 feet. The only wider vertebra I know of is the anterior dorsal of Puertasaurus, at a staggering 168 cm wide (Novas et al. 2005). The Puertasaurus dorsal is also quite a bit taller dorsoventrally, at 106 cm, and it has a considerably larger centrum: 43 x 60 cm, compared to 34 x 43.5 cm for Notocolossus (anterior centrum diameters, height x width).

Centrum size is an interesting parameter. Because centra are so rarely circular, arguably the best way to compare across taxa would be to measure the max area (or, since centrum ends are also rarely flat, the max cross-sectional area). It’s late and this post is already too long, so I’m not going to do that now. But I have been keeping an informal list of the largest centrum diameters among sauropods – and, therefore, among all Terran life – and here they are (please let me know if I missed anyone):

  • 60 cm – Argentinosaurus dorsal, MCF-PVPH-1, Bonaparte and Coria (1993)
  • 60 cm – Puertasaurus dorsal, MPM 10002, Novas et al. (2005)
  • 51 cm – Ruyangosaurus cervical and dorsal, 41HIII-0002, Lu et al. (2009)
  • 50 cm – Alamosaurus cervical, SMP VP−1850, Fowler and Sullivan (2011)
  • 49 cm – Apatosaurus ?caudal, OMNH 1331 (pers. obs.)
  • 49 cm – Supersaurus dorsal, BYU uncatalogued (pers. obs.)
  • 46 cm – Dreadnoughtus dorsal, MPM-PV 1156, Lacovara et al. (2014: Supplmentary Table 1) – thanks to Shahen for catching this one in the comments!
  • 45.6 cm – Giraffatitan presacral, Fund no 8, Janensch (1950: p. 39)
  • 45 cm – Futalognkosaurus sacral, MUCPv-323, Calvo et al. (2007)
  • 43.5 cm – Notocolossus dorsal, UNCUYO-LD 301, González Riga et al. (2016)

(Fine print: I’m only logging each taxon once, by its largest vertebra, and I’m not counting the dorsoventrally squashed Giraffatitan cervicals which get up to 47 cm wide, and the “uncatalogued” Supersaurus dorsal is one I saw back in 2005 – it almost certainly has been catalogued in the interim.) Two things impress me about this list: first, it’s not all ‘exotic’ weirdos – look at the giant Oklahoma Apatosaurus hanging out halfway down the list. Second, Argentinosaurus and Puertasaurus pretty much destroy everyone else by a wide margin. Notocolossus doesn’t seem so impressive in this list, but it’s worth remembering that the “max” centrum diameter here is from one vertebra, which was likely not the largest in the series – then again, the same is true for Puertasaurus, Alamosaurus, and many others.

Notocolossus phylogeny - Gonzalez Riga et al 2016 fig 5

(a) Time-calibrated hypothesis of phylogenetic relationships of Notocolossus with relevant clades labelled. Depicted topology is that of the single most parsimonious tree of 720 steps in length (Consistency Index = 0.52; Retention Index = 0.65). Stratigraphic ranges (indicated by coloured bars) for most taxa follow Lacovara et al.4: fig. 3 and references therein. Additional age sources are as follows: Apatosaurus[55], Cedarosaurus[58], Diamantinasaurus[59], Diplodocus[35], Europasaurus[35], Ligabuesaurus[35], Neuquensaurus[60], Omeisaurus[55], Saltasaurus[60], Shunosaurus[55], Trigonosaurus[35], Venenosaurus[58], Wintonotitan[59]. Stratigraphic ranges are colour-coded to also indicate geographic provenance of each taxon: Africa (excluding Madagascar), light blue; Asia (excluding India), red; Australia, purple; Europe, light green; India, dark green; Madagascar, dark blue; North America, yellow; South America, orange. (b–h) Drawings of articulated or closely associated sauropod right pedes in dorsal (=anterior) view, with respective pedal phalangeal formulae and total number of phalanges per pes provided (the latter in parentheses). (b) Shunosaurus (ZDM T5402, reversed and redrawn from Zhang[45]); (c) Apatosaurus (CM 89); (d) Camarasaurus (USNM 13786); (e) Cedarosaurus (FMNH PR 977, reversed from D’Emic[32]); (f) Epachthosaurus (UNPSJB-PV 920, redrawn and modified from Martínez et al.[22]); (g) Notocolossus; (h) Opisthocoelicaudia (ZPAL MgD-I-48). Note near-progressive decrease in total number of pedal phalanges and trend toward phalangeal reduction on pedal digits II–V throughout sauropod evolutionary history (culminating in phalangeal formula of 2-2-2-1-0 [seven total phalanges per pes] in the latest Cretaceous derived titanosaur Opisthocoelicaudia). Abbreviation: Mya, million years ago. Institutional abbreviations see Supplementary Information. (González Riga et al. 2016: figure 5)

As for the estimated mass of Notocolossus, González Riga et al. (2016) did their due diligence. The sections on mass estimation in the main text and supplementary information are very well done – lucid, modest, and fair. Rather than try to summarize the good bit, I’ll just quote it. Here you go, from page 7 of the main text:

The [humeral] diaphysis is elliptical in cross-section, with its long axis oriented mediolaterally, and measures 770 mm in minimum circumference. Based on that figure, the consistent relationship between humeral and femoral shaft circumference in associated titanosaurian skeletons that preserve both of these dimensions permits an estimate of the circumference of the missing femur of UNCUYO-LD 301 at 936 mm (see Supplementary Information). (Note, however, that the dataset that is the source of this estimate does not include many gigantic titanosaurs, such as Argentinosaurus[5], Paralititan[16], and Puertasaurus[11], since no specimens that preserve an associated humerus and femur are known for these taxa.) In turn, using a scaling equation proposed by Campione and Evans[20], the combined circumferences of the Notocolossus stylopodial elements generate a mean estimated body mass of ~60.4 metric tons, which exceeds the ~59.3 and ~38.1 metric ton masses estimated for the giant titanosaurs Dreadnoughtus and Futalognkosaurus, respectively, using the same equation (see Supplementary Information). It is important to note, however, that subtracting the mean percent prediction error of this equation (25.6% of calculated mass[20]) yields a substantially lower estimate of ~44.9 metric tons for UNCUYO-LD 301. Furthermore, Bates et al.[21] recently used a volumetric method to propose a revised maximum mass of ~38.2 metric tons for Dreadnoughtus, which suggests that the Campione and Evans[20] equation may substantially overestimate the masses of large sauropods, particularly giant titanosaurs. Unfortunately, however, the incompleteness of the Notocolossus specimens prohibits the construction of a well-supported volumetric model of this taxon, and therefore precludes the application of the Bates et al.[21] method. The discrepancies in mass estimation produced by the Campione and Evans[20] and Bates et al.[21] methods indicate a need to compare the predictions of these methods across a broad range of terrestrial tetrapod taxa[21]. Nevertheless, even if the body mass of the Notocolossus holotype was closer to 40 than 60 metric tons, this, coupled with the linear dimensions of its skeletal elements, would still suggest that it represents one of the largest land animals yet discovered.

So, nice work all around. As always, I hope we get more of this critter someday, but until then, González Riga et al. (2016) have done a bang-up job describing the specimens they have. Both the paper and the supplementary information will reward a thorough read-through, and they’re free, so go have fun.

References

Posted by Matt Wedel
Filed in dorsal, humerus, Notocolossus, Puertasaurus, size, stinkin' appendicular elements, titanosaur
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Which was the biggest dinosaur? (Answer: it’s complicated)

October 20, 2015

I just gave an answer to this question on Quora, and it occurred to me that I ought to also give it a permanent home here. So here it is.

This is a great example of a question that you’d think would have a simple, clear answer, but doesn’t. In fact, as a palaeontologist specialising in dinosaur gigantism, I have an abiding fear of being asked this question in a pub quiz, and not being able to produce the name that’s written on the quizmaster’s answer sheet.

First, what do we mean by “biggest”? Diplodocus was longer than Apatosaurus, but Apatosaurus was heavier. Giraffatitan was taller than either. Let’s simplify and assume we want to know the heaviest dinosaur.

Second, estimating the masses of extinct animals is incredibly hard even when we have a pretty complete skeleton. For example, the gigantic mounted brachiosaur skeleton in Berlin (which used to be called “Brachiosaurus” brancai but is now recognised as the separate genus Giraffatitan) has been subject to at least 14 estimates in the published scientific literature, as summarised here. They vary from 13,618 kg to 78,258 kg — a factor of 5.75 for the same individual. That’s like looking at a human skeleton and not knowing whether its from Kate Moss or Arnold Schwazenegger. (There are reasons for this and I urge you to read the linked article.)

Third, the big dinosaurs tend to be very poorly represented. Giraffatitan is probably the heaviest dinosaur known from a more or less complete skeleton (though even that is put together from several different individuals) so I could give that as the answer to the hypothetical pub-quiz — though the answer sheet would probably be out of date and call it Brachiosaurus.

Fourth, which individual of a given species do we mean? I said Giraffatitan is known from a more or less complete skeleton. And my best guess is that that individual massed, say, 30,000 kg. But an isolated fibula of the same species is known that’s 12.6% longer than the one in the skeletal mount. That suggest an animal that masses 1.126^3 = 1.43 times as massive as the mounted skeleton — say 43,000 kg. There might be yet bigger Giraffatitan individuals. On the other hand, there is some evidence that Apatosaurus, which is usually thought of as not being so big, might have got even bigger.

Fifth, the very biggest specimens tend to be known from only a handful of bones. A good example here is the titanosaur Argentinosaurus, which is known from several vertebrae and a few limb bones, but not all from the same individual. It’s a good bet that it massed 60-70 tonnes — so maybe about twice as much as Giraffatitan, but much less than the often-cited 100 tonnes. Other, more recently discovered, titanosaurs seem to be in the same size class: Puertasaurus, Futalognkosaurus, Dreadnoughtus and more. They they are hard to compare directly due to the paucity of overlapping material, or at least described overlapping material. (Scientists are working on getting more of this stuff properly described in the literature, which will help.)

But, sixth, the very biggest dinosaurs tend to be apocryphal. There’s Amphicoelias fragillimus, known only from E. D. Cope’s drawing of the upper half of a single vertebra. This may have been 50 m long and massed 80 tonnes; but other published estimates say 58 m and 122 tonnes. We really can’t say from the very poor remains.

So if you get asked this question in a pub quiz, your best bet is to roll a dice, pick an answer, close your eyes and hope. Roll 1 for Giraffatitan, 2 for Brachiosaurus, 3 for Apatosaurus, 4 for Argentinosaurus, 5 for Dreadnoughtus and 6 for Amphicoelias fragillimus. Good luck!

 

Posted by Mike Taylor
Filed in Ask SV-POW!, mass estimates, size
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How light could a giant azhdarchid be?

October 19, 2015

I imagine that by now, everyone who reads this blog is familiar with Mark Witton’s painting of a giant azhdarchid pterosaur alongside a big giraffe. Here it is, for those who haven’t seen it:

Arambourgiania vs giraffe vs the Disacknowledgement redux Witton ver 2 low res

(This is the fifth and most recent version that Mark has created, taken from 9 things you may not know about giant azhdarchid pterosaurs.)

It’s one of those images that really kicks you in the brain the first time you see it. The idea that an animal the size of a giraffe could fly under its own power seems ludicrous — yet that’s what the evidence tells us.

But wait — what do we mean by “an animal the size of a giraffe”? Yes, the pterosaur in this image is the same height as the giraffe, but how does its weight compare?

Mark says “The giraffe is a big bull Masai individual, standing a healthy 5.6 m tall, close to the maximum known Masai giraffe height.” He doesn’t give a mass, but Wikipedia, citing Owen-Smith (1988), says “Fully grown giraffes stand 5–6 m (16–20 ft) tall, with males taller than females. The average weight is 1,192 kg (2,628 lb) for an adult male and 828 kg (1,825 lb) for an adult female with maximum weights of 1,930 kg (4,250 lb) and 1,180 kg (2,600 lb) having been recorded for males and females, respectively.” So it seems reasonable to use a mass intermediate between those of an average and maximum-sized male, (1192+1930)/2 = 1561 kg.

So much for the giraffe. What does the azhdarchid weigh? The literature is studded with figures that vary wildly, from the 544 kg that Henderson (2010) found for Quetzalcoatlus, right down to the widely cited 70 kg that Chatterjee and Templin (2004) found for the same individual — and even the astonishing 50 kg that seems to be favoured by Unwin (2005:192). In the middle is the 259 kg of Witton (2008).

It occurred to me that I could visualise these mass estimates by shrinking the giraffe in Mark’s image down to the various proposed masses, and seeing how credible it looks to imagine these reduced-sized giraffes weighting the same as the azhdarchid. The maths is simple. For each proposed azhdarchid mass, we figure out what it is as a proportion of the giraffe’s 1561 kg; then the cube root of that mass proportion gives us the linear proportion.

  • 544 kg = 0.389 giraffe masses = 0.704 giraffe lengths
  • 259 kg = 0.166 giraffe masses = 0.549 giraffe lengths
  • 70 kg =0.0448 giraffe masses = 0.355 giraffe lengths

Let’s see how that looks.

Arambourgiania vs giraffe vs the Disacknowledgement redux Witton ver 2 low res

On the left, we have Mark’s artwork, with the giraffe massing 1561 kg. On the right, we have three smaller (isometrically scaled) giraffes of masses corresponding to giant azhdarchid mass estimates in the literature. If Don Henderson (2010) is right, then the pterosaur weighs the same as the 544 kg giraffe, which to me looks pretty feasible if it’s very pneumatic. If Witton (2008) is right, then it weighs the same as the 259 kg giraffe, which I find hard to swallow. And if Chatterjee and Templin (2004) are right, then the giant pterosaur weighs the same as the teeny tiny 70 kg giraffe, which I find frankly ludicrous. (For that matter, 70 kg is in the same size-class as Georgia, the human scale-bar: the idea that she and the pterosaur weigh the same is just silly.)

What is the value of such eyeball comparisons? I’m not sure, beyond a basic reality check. Running this exercise has certainly made me sceptical about even the 250 kg mass range which now seems to be fairly widely accepted among pterosaur workers. Remember, if that mass is correct then the pterosaur and the 259 kg giraffe in the picture above weight the same. Can you buy that?

Or can we find extant analogues? Are there birds and mammals with the same mass that are in the same size relation as these images show?

References

  • Chatterjee, Sankar, and R. J. Templin. 2004. Posture, locomotion, and paleoecology of pterosaurs. Geological Society of America, Special Paper 376. 68 pages.
  • Henderson, Donald M. 2010. Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology 30(3):768-785.
  • Witton, Mark P. 2008. A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana 28:143-159.
Posted by Mike Taylor
Filed in Art, giraffe, Just Plain Wrong, life restorations, Mark Witton, mass estimates, math, People we like, size, stinkin' pterosaurs
31 Comments »

Will we ever find the biggest dinosaur?

June 12, 2015

I was contacted recently by David Goldenberg (dgoldenberg@gmail.com), a journalist who’s putting together a piece on the biggest dinosaurs. He asked me a few questions, and since I’d taken the time to write answers I thought I may as well post them here.

1) Do you think that we will ever know what the largest dinosaur (by mass) was?

In principle, we can never know that we’ve found the largest dinosaur. All we can know (and we probably can’t really know even this, as we’ll see below) is that we’ve found the largest so far. If we were dealing with animals where there’s a good sample size, there would be statistical techniques that we could use to figure out the likely size-range. But most giant dinosaur species are known only a handful of specimens — sometimes only a single one. How big did Puertasaurus get? We can’t possibly say: the best we can do is estimate how big the one known specimen of Puertasaurus was.

That said, we can sort of get a feel for size classes. There are quite a few sauropods that seem to come in at around 30-40 tonnes — Brachiosaurus, Giraffatitan, Supersaurus, Dreadnoughtus — which suggests there might be some kind of a limit there. But there are bigger titanosaurs (Argentinosaurus, Puertasaurus, Futalognkosaurus) which show that if the barrier exists at all, it’s a “soft” one. And of course the tantalising hints of super-giant sauropods.

There are at least three of these: Amphicoelias fragillimus, a diplodocid known from a drawing of a vertebral arch which has since been lost or destroyed, which could well have massed 100 tonnes. Bruhathkayosaurus, a giant titanosaur known from a two-meter tibia, since destroyed, which could conceivably have massed twice that; and the Broome Sandstone track-maker, known only from footprints, which might have been somewhere in between.

Any one of those, we might write off and say it’s too good to be true — all three stories are pretty vague as to evidence and require a lot of guesswork in the inferences. But the fact that we have all three of these makes me feel pretty certain that there were indeed sauropods out there in the 100-200 tonne range (i.e. the size of big whales). I only hope we find solid, verifiable, curated evidence for them some time soon.

2) What bones do you need to have before you can make an accurate measurement?

You can’t ever make an accurate measurement. Consider even a really well represented, essentially complete specimen such as MB.R.2181 (previously known as HM S II), the giant mounted skeleton in the Museum für Naturkunde Berlin. Peer-reviewed published estimates of the mass of that one individual have varied between 13,618 and 78,258 kg — a factor of 5.75. Even if you discard these obvious outlier estimates, recent and credible estimates vary from 23,337 to 38,000 kg, which is still a factor of 1.63.

And this is not completely crazy. Two humans with essentially identical skeletons can weigh 70 and 114 kg, after all. Soft tissue is essentially impossible to predict.

3) What do you make of the fact that so many different species have been given the title? Is that the fault of the media or scientists or what?

A big part of is that it depends on what you count. That Berlin brachiosaur is the biggest dinosaur known from an essentially complete skeleton, so Giraffatitan is a legitimate holder of the crown. (Confusing matters further, it used to be thought to be a species of Brachiosaurus). But there were definitely bigger sauropods than that — just not known from such complete specimens. Argentinosaurus was certainly bigger, for example. But there’s no way to put a meaningful whole-body mass estimate on it.

But yes, there is also an understandable tendency towards sensationalism, both from scientists and the press. There have been plenty of new discoveries that can legitimately be described as “could be the biggest yet”.

Posted by Mike Taylor
Filed in recycled, size
8 Comments »

How big was ‘Huanghetitan’ ruyangensis? I mean, really?

March 3, 2015

I’ve been taking a long-overdue look at some of the recently-described giant sauropods from China, trying to sort out just how big they were. Not a new pursuit for me, just one I hadn’t been back to in a while. Also, I’m not trying to debunk anything about this animal – as far as I know, there was no bunk to begin with – I’m just trying to get a handle on how big it might have been, for my own obscure purposes.

‘Huanghetitan’ ruyangensis was named by Lu et al. (2007) on the basis of a sacrum, the first 10 caudal vertebrae, some dorsal ribs and haemal arches, and a partial ischium. The holotype is 41HIII-0001 in the Henan Geological Museum. Lu et al. (2007) referred the new animal to the genus Huanghetitan, which was already known from the type species H. liujiaxiaensis (You et al., 2006). However, Mannion et al. (2013) found that the two species are not sister taxa and therefore ‘H.’ ruyangensis probably belongs to another genus, which has yet to be erected. Hence my use of scare quotes around the genus name.

Huanghetitan ruyangensis sacrum comparison

Here’s the sacrum of ‘H.’ ruyangensis from Lu et al. (2007: fig. 2). The original small scale bar is supposed to be 10cm. You know how I feel about scale bars (or maybe you don’t, in which case read this and this), but in this case the scale seems pretty legit based on limited measurements that are also given in the paper. I comped in the sacrum of Brachiosaurus altithorax FMNH P25107 from this post (many thanks to Phil Mannion for the photos!), and scaled it according to the max width across the second pair of sacral ribs, which Riggs (1904: p. 236) gives as 105 cm. The sacrum of ‘H.’ ruyangensis is a little bigger, but not vastly bigger. ‘H.’ ruyangensis had six sacrals to Brachiosaurus‘s five, so extra length is mostly illusory, whereas the extra width is mostly legit.

According to Lu et al. (2007), the anterior face of the first caudal vertebra in ‘H.’ ruyangensis measures 26.9 cm tall by 32 cm wide, and the centrum is 18.2 cm long. The same measurements in Brachiosaurus are 28 x 33 cm for the anterior face and 16 cm for the centrum length. It’s basically a tie.

What about the big rib? Lu et al. (2007) show a complete dorsal rib of ‘H.’ ruyangensis that is 293 cm long. That’s nothing to sniff at – the longest rib of Brachiosaurus, and the cause for the specific name altithorax (‘tall-bodied’), measures 274.5 cm, so the ‘H.’ ruyangensis rib is about 7% longer. But it’s not the longest rib known for any sauropod. As far as I know, that honor goes to a Supersaurus dorsal rib measuring 305 cm (Lovelace et al., 2008). The biggest Supersaurus caudal also blows away the caudals of both ‘H.’ ruyangensis and Brachiosaurus, with a anterior face 39 cm tall by 46 cm wide. But then diplodocids were all about that bass, so there’s not much point in comparing tail size with a titanosauriform if you’re trying to get a handle on overall body size. Still, the 35-40 ton Supersaurus shows that you can have 3-meter ribs without being anywhere near Argentinosaurus territory, mass-wise.

So what’s the verdict? ‘H.’ ruyangensis was a little bigger than the holotype of Brachiosaurus altithorax, but only by a few percent. It might have been about the same size as the XV2 specimen of Giraffatitan brancai. Or, who knows, it could have had completely different proportions and massed considerably more (or less). But on the current evidence, it doesn’t seem to have been one of the biggest sauropods of all time. I hope we get some more of it one of these days.

References

 

Posted by Matt Wedel
Filed in brachiosaurids, Brachiosaurus, sacral, size
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