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.


This just in, from Zurriaguz and Powell’s (2015) hot-off-the-press paper describing the morphology and pneumatic features of the presacral column of the derived titanosaur Saltasaurus. (Thanks to Darren for bringing this paper to my attention.)

Now, as everyone knows, titanosaurs don’t have epipophyses. In fact, they’re the one major sauropod group where Matt has not observed them.

Until today.

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Look at the left postzygapophysis, at top left of this image. Doesn’t that look like there’s a distinct rounded eminence sticking out towards the camera?

No? Not convinced? All right, then, how about this?

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

This time, look at the right postzyg (again at top left in the image). Doesn’t that look like there are two separate bony structures up there separated by a notch? A postzygapophyseal facet below, and an epipophysis above? Right?

Huh? What’s that? Just damage, you say?

All right. Let’s bring out the smoking gun.

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it's in the original.)

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it’s in the original.)

Again up at top left, we seem to have a clear case of a ventrally directed postzygapophyseal facet surmounted by a separate eminence which can only be an epipophysis. It even seems to be roughened for tendon attachment.

What does this mean? Only the same thing we said last time: The more we look for epipophyses, the more we find them. Amazing how often that turns out to be true of various things.

We seem to be headed towards the conclusion that epipophyses, while never ubiquitous, pop up in all sorts of places scattered all across the ornithodiran tree, encompassing birds, other theropods, sauropods, prosauropods, several groups of ornithischians, and both pterodactyloid and “rhamphorhynchoid” pterosaurs.

But what about outside Ornithodira?

Can we find epipophyses even out there, in the wilderness?

Stay tuned!


In a comment on the last post, on the mass of Dreadnoughtus, Asier Larramendi wrote:

The body mass should be considerably lower because the reconstructed column don’t match with published vertebrae centra lengths. 3D reconstruction also leaves too much space between vertebrae. The reconstruction body trunk is probably 15-20% longer than it really was. Check the supplementary material:

So I did. The table of measurements in the supplementary material is admirably complete. For all of the available dorsal vertebrae except D9, which I suppose must have been too poorly preserved to measure the difference, Lacovara et al. list both the total centrum length and the centrum length minus the anterior condyle. Centrum length minus the condyle is what in my disseration I referred to as “functional length”, since it’s the length that the vertebra actually contributes to the articulated series, assuming that the condyle of one vertebra sticks out about as far as the cotyle is recessed on the next vertebra. Here are total lengths/functional lengths/differences for the seven preserved dorsals, in mm:

  • D4 – 400/305/95
  • D5 – 470/320/150
  • D6 – 200/180/20
  • D7 – 300/260/40
  • D8 – 350/270/80
  • D9 – 410/ – / –
  • D10 – 330/225/105

The average difference between functional length and total length is 82 mm. If we apply that to D9 to estimate it’s functional length, we get 330mm. The summed functional lengths of the seven preserved vertebrae are then 1890 mm. What about the missing D1-D3? Since the charge is that Lacovara et al. (2014) restored Dreadnoughtus with a too-long torso, we should be as generous as possible in estimating the lengths of the missing dorsals. In Malawisaurus the centrum lengths of D1-D3 are all less than or equal to that of D4, which is the longest vertebra in the series (Gomani 2005: table 3), so it seems simplest here to assign D1-D3 functional lengths of 320 mm. That brings the total functional length of the dorsal vertebral column to 2850 mm, or 2.85 m.

At this point on my first pass, I was thinking that Lacovara et al. (2014) were in trouble. In the skeletal reconstruction that I used for the GDI work in the last post, I measured the length of the dorsal vertebral column as 149 pixels. Divided by 36 px/m gives a summed dorsal length of 4.1 m. That’s more than 40% longer than the summed functional lengths of the vertebrae calculated above (4.1/2.85 = 1.44). Had Lacovara et al. really blown it that badly?

Before we can rule on that, we have to estimate how much cartilage separated the dorsal vertebrae. This is a subject of more than passing interest here at SV-POW! Towers–the only applicable data I know of are the measurements of intervertebral spacing in two juvenile apatosaurs that Mike and I reported in our cartilage paper last year (Taylor and Wedel 2013: table 3, and see this post). We found that the invertebral cartilage thickness equaled 15-24% of the length of the centra.* For the estimated 2.85-meter dorsal column of Dreadnoughtus, that means 43-68 cm of cartilage (4.3-6.8 cm of cartilage per joint), for an in vivo dorsal column length of 3.28-3.53 meters. That’s still about 15-20% shorter than the 4.1 meters I measured from the skeletal recon–and, I must note, exactly what Asier stated in his comment. All my noodling has accomplished is to verify that his presumably off-the-cuff estimate was spot on. But is that a big deal?

Visually, a 20% shorter torso makes a small but noticeable difference. Check out the original reconstruction (top) with the 20%-shorter-torso version (bottom):

Dreadnoughtus shortened torso comparison - Lacovara et al 2014 fig 2

FWIW, the bottom version looks a lot more plausible to my eye–I hadn’t realized quite how weiner-dog-y the original recon is until I saw it next to the shortened version.

In terms of body mass, the difference is major. You’ll recall that I estimated the torso volume of Dreadnoughtus at 32 cubic meters. Lopping off 20% means losing 6.4 cubic meters–about the same volume as a big bull elephant, or all four of Dreadnoughtus‘s limbs put together. Even assuming a low whole-body density of 0.7 g/cm^3, that’s 4.5 metric tons off the estimated mass. So a ~30-ton Dreadnoughtus is looking more plausible by the minute.

For more on how torso length can affect the visual appearance and estimated mass of an animal, see this post and Taylor (2009).

* I asked Mike to do a review pass on this post before I published, and regarding the intervertebral spacing derived from the juvenile apatosaurs, he wrote:

That 15-24% is for juveniles. For the cervicals of adult Sauroposeidon we got about 5%. Why the differences? Three reasons might be relevant: 1, taxonomic difference between Sauroposeidon and Apatosaurus; 2, serial difference between neck and torso; 3, ontogenetic difference between juvenile and adult. By applying the juvenile Apatosaurus dorsal measurement directly to the adult Dreadnoughtus dorsals, you’re implicitly assuming that the adult/juvenile axis is irrelevant (which seems unlikely to me), that the taxonomic axis is (I guess) unknowable, and that the cervical/dorsal distinction is the only one that matter.

That’s a solid point, and it deserves a post of its own, which I’m already working on. For now, it seems intuitively obvious to me that we got a low percentage on Sauroposeidon simply because the vertebrae are so long. If the length-to-diameter ratio was 2.5 instead of 5, we’d have gotten 10%, unless cartilage thickness scales with centrum length, which seems unlikely. For a dorsal with EI of 1.5, cartilage thickness would then be 20%, which is about what I figured above.

Now, admittedly that is arm-waving, not science (and really just a wordy restatement of his point #2). The obvious thing to do is take all of our data and see if intervertebral spacing is more closely correlated with centrum length or centrum diameter. Now that it’s occurred to me, it seems very silly not to have done that in the actual paper. And I will do that very thing in an upcoming post. For now I’ll just note three things:

  1. As you can see from figure 15 in our cartilage paper, in the opisthocoelous anterior dorsals of CM 3390, the condyle of the posterior vertebra is firmly engaged in the cotyle of the anterior one, and if anything the two vertebrae look jammed together, not drifted apart. But the intervertebral spacing as a fraction of centrum length is still huge (20+4%) because the centra are so short.
  2. Transferring these numbers to Dreadnoughtus only results in 4.3-6.8 cm of cartilage between adjacent vertebrae, which does not seem unreasonable for a 30- or 40-ton animal with dorsal centra averaging 35 cm in diameter. If you asked me off the cuff what I thought a reasonable intervertebral spacing was for such a large animal, I would have said 3 or 4 inches (7.5 to 10 cm), so the numbers I got through cross-scaling are actually lower than what I would have guessed.
  3. Finally, if I’ve overestimated the intervertebral spacing, then the actual torso length of Dreadnoughtus was even shorter than that illustrated above, and the volumetric mass estimate would be smaller still. So in going with relatively thick cartilage, I’m being as generous as possible to the Lacovara et al. (2014) skeletal reconstruction (and indirectly to their super-high allometry-derived mass estimate), which I think is only fair.



How massive was Dreadnoughtus?

September 11, 2014

Dreadnoughtus published body outline - Lacovara et al 2014 fig 2

In the paper describing the new giant titanosaur Dreadnoughtus, Lacovara et al. (2014) use the limb bone allometry equation of Campione and Evans (2012) to derive a mass estimate for the holotype individual of 59.3 metric tons. This is presumably the “middle of the road” value spat out by the equation; the 95% confidence interval on either side probably goes from 40 to 80 metric tons or maybe even wider.

I decided to see if 59 metric tons was plausible for Dreadnoughtus by doing Graphic Double Integration (GDI) on the published skeletal reconstruction and body outline (Lacovara et al. 2014: fig. 2). The image above is the one I used, so if you like, you can check my numbers or try your hand at GDI and see what you get.

First up, I have to congratulate Lacovara et al. for the rare feat of having everything pretty much to scale, and a properly-sized scale bar. This is not always the case. Presumably having a 3D digital model of the reconstructed skeleton helped — and BTW, if you haven’t downloaded the 3D PDFs and played with them, you are missing out bigtime.

Here are my measurements of various bits in the picture and the scale factors they give:

Meter scale bar: 37 pixels – 1.0 meters – 37 px/m
Human figure: 66 pixels – 1.8 meters – 37 px/m
Scapula: 62 pixels – 1.7 meters – 36 px/m
Humerus: 58 pixels – 1.6 meters – 36 px/m
Femur: 70 pixels – 1.9 meters – 37 px/m
Cervical: 45 pixels – 1.1 meters – 41 px/m (not included in average*)
Neck: 407 pixels – 11.3 meters – 36 px/m
Post-cervical vertebral column: 512 pixels – 13.8 meters – 37 px/m
Total length: 922 pixels – 26.0 meters – 35 px/m
AVERAGE 36 px/m

* I didn’t include the cervical because when I measured it I sorta guessed about where the condyle was supposed to be. That was the odd measurement out, and I didn’t want to tar Lacovara et al. for what might well be my own observer error.

Dreadnoughtus decomposed for GDI - Lacovara et al 2014 fig 2

Here’s the chopped-up Dreadnoughtus I used for my estimate. Just for the heck of it, for the first time out I assigned all of the body regions circular cross-sections. We’ll come back to how realistic this is later. Here’s what I got for the volumes of the various bits:

Head: 0.2 m^3
Neck: 13.9
Body: 32.1
Tail: 4.0
Limbs: 6.8
TOTAL: 57.0 m^3

Okay, this is looking pretty good, right? Lacovara et al. (2014) got 59.3 metric tons using limb allometry, I got a volume of 57 cubic meters using GDI. If Dreadnoughtus was the same density as water — 1 metric ton per cubic meter — then my estimated mass would be 57 tons, which is crazy close given all of the uncertainties involved.

BUT there are a couple of big buts involved. The first is that a lot of sauropods had distinctly non-round body cross-sections (Diplodocus, Camarasaurus). So assuming circular cross-sections might inflate the body well beyond its likely volume. Second is that sauropods were probably much less dense than water (discussed here, here, and here, and see Wedel 2005 for the full scoop). What are the implications for Dreadnoughtus?

Round and Round

It turns out that circular cross-sections are probably defensible for some parts of Dreadnoughtus. By playing around with the 3D PDF of the assembled skeleton I was able to get these orthogonal views:

Dreadnoughtus 3D skeleton orthogonal views

I don’t remember what the pixel counts were for the max height and max width of the torso, but they were pretty close. I measured at several points, too: front of the pelvis, max extent of ribcage, mid-scap. This is probably not super-surprising as the fatness of titanosaurs has been widely noted before this. Here’s a cross-section through the torso of Opisthocoelicaudia at D4 (Borsuk-Bialynicka 1977: fig. 5) — compare to the more taconic forms of Diplodocus and Camarasaurus linked above.

Opisthocoelicaudia torso x-s - Borsuk-Bialynicka 1977 fig 5

Okay, a round torso on Dreadnoughtus I can buy. A round neck and tail, not so much. Look at the skeletal recon and you can see that even with a generous allowance for caudofemoralis muscles on the tail, and diapophyses on the cervical vertebrae, no way were those extremities circular in cross-section. Just off the cuff I think a width:height ratio of 2:3 is probably about right.

But there are some body regions that probably were round, or close enough as to have made no difference, like the head and limbs. So I actually toted up the volume three times: once with circular cross-sections throughout (probably too fat), once with a 2:3 width:height ratio in the neck, trunk, and tail (probably too thin, at least in the torso), and once with the 2:3 ratio only in the neck and tail (my Goldilocks version). Here are the numbers I got:

Dreadnoughtus Table 1 three volumes


Air Apparent?

Now, for density. Birds are usually much less dense than water — lotsa cited data in this hummingbird post, the punchline of which is that the average whole-body density of a bunch of birds is 0.73 g/cm^3. Why so light? In part because the lungs and air sacs are huge, and account for 15-20% of the whole-body volume, and in part because many of the bones are pneumatic (= air-filled). For a really visceral look at how much air there can be in the bones of birds, see this post, and this one and this one for sauropods.

In my 2005 paper (almost a decade old already — gosh!), I found that for Diplodocus, even a fairly conservative estimate suggested that air inside the bones accounted for about 10% of the volume of the whole animal in life. That may be higher than in a lot of birds, because sauropods were corn-on-the-cob, not shish-kebabs. And that’s just the air in the bones — we also have several lines of evidence suggesting that sauropods had air-sacs like those of birds (Wedel 2009). If the lungs and air sacs occupied 15% of the volume of the whole animal, and the air in the bones occupied another 10%, that would give a whole-body density pretty close to the 0.73 g/cm^3 found for birds. Sauropods might have been lighter still — I didn’t include visceral, intermuscular, or subcutaneous diverticula in my calculations, because I couldn’t think of any way to constrain their volumes.

What about Dreadnoughtus? As Lacovara et al. (2014) describe, the cervical, dorsal, and sacral vertebrae and sacral ribs are honeycombed with pneumatic camellae (small, thin-walled chambers). And the dorsal ribs have pneumatic foramina and were probably at least partly hollowed-out as well. The caudal vertebrae do not appear to have been pneumatic, at least internally (but diverticula going into the tail can be cryptic — see Wedel and Taylor 2013b). Diplodocus has a big, long, highly pneumatic tail, but Dreadnoughtus has a much longer neck, both proportionally and absolutely, and pneumatic dorsal ribs. So this one may be too close to call. But I also ran the numbers for T. rex way back when and found that air in its vertebrae accounted for 7% of its body volume (this abstract). Pessimistically, if we assume Dreadnoughtus had small lungs and air sacs (maybe 10% of whole-body volume) and not much air in the bones (7%), it’s whole-body density was probably still closer to 0.8 g/cm^3 than to 0.9. Optimistically, a lot of titanosaurs were radically pneumatic and they have may have had big air sac systems and extensive diverticula to match, so a bird-like 0.7-0.75 g/cm^3 is certainly not beyond the bounds of possibility.

Dreadnoughtus Table 2 twelve masses

This table shows a spectrum of masses, based on the three body volumes from GDI (columns) and some possible whole-body densities (rows). Note that the columns are not in the same order as in the first table — I lined them up from most t0 least voluminous here. The 57-ton estimate is the max, and that assumes that the neck and tail were both perfectly round, and that despite the lungs, air sacs, and air reservoirs inside the bones, the whole-body density of Dreadnoughtus was still 1.0 g/cm^3, neither of which are likely (or, I guess, that a real Dreadnoughtus was significantly fatter than the one shown, and that all of that extra bulk was muscle or some other heavy tissue). The 28t mass in the lower left corner is also unrealistic, because it assumes a tall, narrow torso. My pick is the 36t estimate at the bottom of the middle column, derived from what I think are the most defensible volume and density. Your thoughts may differ — the comment thread is open.

Roll Your Own

Dreadnoughtus Table 3 body region comparison

This last table is just a quick-and-dirty comparison of how the volume of the body breaks down among its constituent parts in Plateosaurus (from this post), Giraffatitan (from Taylor 2009), and Dreadnoughtus (based on my “tall neck and tail” GDI). Dreadnoughtus seems to have a more voluminous neck and a less voluminous trunk, proportionally, than Giraffatitan, but I think a lot of that is down to the very fat fleshy envelope drawn around the cervicals of Dreadnoughtus. We are fortunate to count some fearsomely talented paleoartists among our readers — I’ll look forward to seeing what you all come up with in your independent skeletal recons.

So, what’s the take-home? Based on the data available, I don’t think the holotype individual of Dreadnoughtus massed anything like 59 metric tons. I think 35-40 metric tons is much more defensible. But I’m happy to have my errors pointed out and new data and arguments brought to the fore. Your thoughts are most welcome.


I just read Mark Witton’s piece on the new new titanosaur Rukwatitan (as opposed to the old new titanosaur Dreadnoughtus). I was going to write something about it, but I realised that Mark has already said everything I would have, but better. So get yourselves over to his piece and enjoy the titanosaurianness of it all!

Podageddon low res Witton

Yay, vertebrae! Lacovara et al. (2014: fig. 1)

Yay, vertebrae! Lacovara et al. (2014: fig. 1)

Mike and I are in York for SVPCA — more on that soonish — and I just wanted to get out some quick thoughts about the world’s newest giant sauropod.

First off, the paper (Lacovara et al. 2014) is open access, which is great. And, hey, 3D PDFs of the whole skeleton and selected elements — I’m going to be having some fun with those.

And given that this is a short initial descriptive paper, I was really happy to see a reasonably detailed table of measurements. The materials and methods section at the end spells out explicitly how the team arrived at their estimates of the animal’s length and mass. All of that looks very solid, and it’s more information that we often get in these short initial descriptions. So although I will look forward to seeing a complete osteological description of Dreadnoughtus in the future, this first paper is better than a lot of similar papers in that it includes a lot of actually useful information.

As for whether Dreadnoughtus was the world’s heaviest sauropod — how could anyone possibly tell? The femur of Dreadnoughtus is 1.9 meters, which is only three-quarters of the estimated length of the largest partial femur of Argentinosaurus. Now, there is plenty of evidence from both histology and macro-level indicators of skeletal age that the holotype individual was still growing, but how much bigger was it going to get, 10%, 25%? I think that given its size, completeness, and immature state it is fair to discuss Dreadnoughtus in the same breath as Argentinosaurus, Puertasaurus, the largest specimens of Alamosaurus, and other giant sauropods. But I think any claim that it is ‘the’ heaviest is premature until we know how big a fully adult Dreadnoughtus was.

Dreadnoughtus and kin. Lacovara et al. (2014: fig. 3)

Dreadnoughtus and kin. Lacovara et al. (2014: fig. 3)

Here’s a weird thing: according to Table 1, the 113-cm cervical vertebra of Dreadnoughtus is the longest known among titanosauriforms. But the longest cervical of Sauroposeidon has a 125-cm centrum, and Sauroposeidon always comes out as a titanosauriform in phylogenetic analyses, including the one in the Dreadnoughtus paper. The estimated 2.5-meter femur of Argentinosaurus reported by Mazzetta et al. (2004) is also not listed in that table, although some estimated lengths for other incomplete elements are given. I don’t think there’s any conspiracy here — it is actually quite a challenge to keep up with all of the relevant numbers — but I would like to have seen a bit more thoroughness in reporting measurements of other sauropods where at least some individual elements are larger than in Dreadnoughtus.

Anyway, as we found for the next-most-recent “world’s largest dinosaur” earlier this year, Dreadnoughtus does not extend the known size range of the largest sauropods. Period. Anyone who says definitively otherwise is actually making assumptions about ontogeny and mass estimation that just aren’t justified.

Does that mean that Dreadnoughtus isn’t interesting? Of course not! For one thing, now we can start talking intelligently about the body proportions of these giant titanosaurs. Up until now we’ve had a good idea of what other, smaller sauropods looked like, things like Mamenchisaurus, Diplodocus, and Giraffatitan, and we’ve had reasonably complete skeletons of small titanosaurs such as Malawisaurus and Rapetosaurus, but we haven’t had a very clear idea of the proportions of the largest titanosaurs (sometimes because of conflicting measurements). So now we can start investigating questions involving the biomechanics and hopefully the growth trajectories of giant titanosaurs, which were more in the realm of speculation until now. There are some tantalizing hints toward this in the current paper — for example, the authors mention that a lot of the bones preserve muscle attachments. That would be a fascinating study in its own right, just knowing what the muscle attachments can tell us about the soft-tissue anatomy of Dreadnoughtus, and in turn what soft tissue can tell us about how the muscles and joints worked.

Big and getting bigger: the limb bones of Dreadnoughtus. Lacovara et al. (2014: fig. 2)

Big and getting bigger: the limb bones of Dreadnoughtus. Lacovara et al. (2014: fig. 2)

There are myriad interesting questions dealing with the ability of the limb bones and vertebrae to support the mass of the body and how that skeletal support changed, both over the lifespan of an animal and over evolutionary time. Now, there is a limit to how much Dreadnoughtus can add here, since it’s only known by two individuals that weren’t radically different in size, but given how bleak the data landscape is for giant titanosaurs, it’s an important addition to our knowledge.

In conclusion, although I have some reservations about overlooked measurements of some other giant sauropods, and although the media-driven Dreadnoughtus-vs-Argentinosaurus pissing contest is pointless, I’m excited about this first paper. And I’m looking forward to more, both more complete descriptive work, and functional and biomechanical analyses building on that. Happy days.


You’ve probably seen a lot of yapping in the news about a new “world’s largest dinosaur”, with the standard photos of people lying down next to unfeasibly large bones. Here’s my favorite–various versions of it have been making the rounds, but I grabbed this one from Nima’s post on his blog, The Paleo King.


The first point I need to make here is that photos like these are attention-grabbing but they don’t really tell you much. Partly because they’re hard to interpret, and partly because they almost always look more impressive than they really are. For example, I am 6’2″ tall (1.88 meters). If I lie down next to a bone that is 7’2″ (219 cm) 6’8″ (203 cm) long, it is going to look ungodly huge–a full half a foot longer than I am tall. But that is the length of the femur of the Brachiosaurus holotype–we’ve known of sauropod femora that big for a century now. People get tripped up by this sort of thing all the time–even scientists. Update: even me! Somehow I had gotten it into my head that the Brachiosaurus femur was 219 cm, when it is actually 203 cm. That goof doesn’t affect any of what follows, because from here on down I used Argentinosaurus as the point of reference.

Second point: at least some of the reporting on this new find has been unusually–and refreshingly–nuanced. The first news story I read about it was this one, which gives Paul Barrett plenty of airtime to explain why we should be cautious about jumping to any conclusions regarding the size of the new animal. That will turn out to be prophetic.

But let’s get back to that photo. Just eyeballing it, it looks like the femur is about half again as long as the dude is tall (the dude, BTW, is Pablo Puerta, for whom Puertasaurus is named). I was reading Nima’s post and he guessed that the femur was in the neighborhood of 3 meters, which would be a significant size increase over the next-biggest sauropod known from fossils that still exist (i.e., not including semi-apocraphyal gigapods like Amphicoelias fragillimus and Bruhathkayosaurus). The current based-on-existing-fossils record-holder is Argentinosaurus–there is a partial femur that would have been about 2.5 meters long when complete. So a 3-meter femur would be a wonderful thing. But alas, it just ain’t so–or at least the one in the photo isn’t anywhere near that big. Allow me to demonstrate.

femur_pablo with measurements

Here’s another copy of the photo with some measurements applied. There is no actual scale bar in the picture, but we can use the dimensions of the things we can see to figure some stuff out.

For starters, there is a lot of perspective distortion going on here. Pallet B is 350 pixels wide at the near end, 280 pixels at the far end–a difference of 20%. I didn’t put the far-end measurement for Pallet A into the picture, but from corner to corner it is 295 pixels.

Shipping pallets vary in size around the world, but in the US the most common size is 48 x 40 inches. Other countries use different sizes, mostly smaller; I am unaware of any standard shipping pallets larger than 48×40. So assuming that the ones in the picture are that size is actually a liberal assumption that will lead to large estimates–if the pallets are smaller than 48×40, then all of the dimensions I’m about to calculate will be smaller as well. Obviously the pallets have their narrow ends facing us, which is nice because 40 inches is almost exactly 1 meter. So we can divide other things in the picture by pallet length and get their dimensions in meters.

The near side of the femur is pretty much in line with the stringer running left-to-right down the middle of Pallet A. From the measurements of the ends of that pallet, we’d expect the middle-distance width to be about 330 pixels, and in fact I got 335. The 830-pixel line I drew on the near side is not the total length of the bone–you could add a bit more for the femoral head, to a max of maybe 860 or 870 pixels. Divide that by 335 and you get a max length of about 2.6 meters.

The 800-pixel line for the far side of the femur goes from the top of the head to the bottom of the medial condyle, so there’s no extending needed there. That line is at about the mid-point of Pallet B, or about 315 pixels. If Pallet B is a meter wide, the femur is 2.5 meters long.

We can also check things by trying to figure out how tall Pablo Puerta is. At first that looks more encouraging for the possibility that this is a record-breaker. If we assume the femur really is 3 meters long, and compare the 800-pixel femur line to the 500-pixel Pablo line, Pablo is 62.5% the length of the femur, or 1.87 meters–about the same height as me. That would be pretty tall for an Argentinian, but it’s certainly plausible.

But that’s not a legit comparison, because Pablo is farther from the camera than is the femur. Look at Pallet A–we can use the slats as perspective guides to help figure out where the proximal end of the femur ought to be if projected back to Pablo’s distance from the camera. If we do that at both ends, the length of the femur if placed where Pablo is lying would be 750 pixels or fewer, which would make Pablo at least 2 meters tall. People get a lot taller than that, but it would make him unusually tall, and if you’re trying to emphasize how big your sauropod is, you probably won’t pick the tallest person in the room to pull a Jensen. If we assume Pablo’s about 5’8″–average height for an Argentinian male–then the femur is about 2.6 meters long, which is consistent with the estimates from the pallets. He could well be shorter, in which the case the femur might also be shorter.

There are of course vast amounts of uncertainty in all of this. I have heard the number 2.4 meters thrown around in the media, which is within the margin of error of my crude estimates here–I deliberately skewed large at most decision points to give the hypothesized 3-meter femur the best possible chance. I have to emphasize that this is not how you do science–I’m deliberately doing this quick and dirty. But even using these admittedly flawed and somewhat goofy methods, it’s easy to show that the femur isn’t 3 meters long, or anywhere near it.

So, three last points:

  1. As the post title implies, the new Argentine titanosaur is about the same size as Argentinosaurus. That shouldn’t be too surprising, since the mass estimates that have been quoted in the media are within a few percent of the mass estimates for Argentinosaurus. The new critter might be a hair bigger, but it doesn’t “smash” the record, and when we get actual measurements it could end up being smaller than Argentinosaurus in linear dimensions. I note that the size trumpeted in the media is a mass estimate based on femoral fatness, not femoral length. You’d think that if the biggest femur was demonstrably longer than the 2.5-meter Argentinosaurus femur, they’d lead with that. So the reporting so far is also consistent with an animal about the same size as Argentinosaurus.
  2. That is in no way a disappointing result! That biggest Argentinosaurus femur is incomplete, so the 2.5-meter length is an estimate. Even if the big femur shown here is only (only!) 2.4 meters long, it’s still the longest complete limb bone from anything, ever. And even if the new animal is identical to Argentinosaurus in size, there’s still a lot more of it, so we’ll get a better idea of what these super-gigantic titanosaurs looked like. That’s a big win.
  3. Finally, this is not a case of MYDD. There’s no paper yet, and I don’t blame the team for not making the measurements public until the work is done. I also don’t blame them for publicizing the find. So far, this seems to be exactly what they’re saying it is–an animal about the size of Argentinosaurus, and maybe just a hair bigger. That’s cool. I wish them the best of luck writing it up. I almost wrote “I can’t wait to see the paper” but actually I can–something like this, I’d rather they take their time and do it right. It may not be a record-smasher, but it’s a solid, incremental advance, and science needs those, too.



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