Out today: a new Turiasaurian sauropod, Mierasaurus bobyoungi, from the Early Cretaceous Cedar Mountain formation in Utah. This comes to us courtesy of a nice paper by Royo Torres et al. (2017),

Royo-Torres et al. 2017, fig. 3. The postcranial skeleton (UMNH.VP.26004) of Mierasaurus bobyoungi gen. nov, sp. nov. with the following elements: (a) middle cervical vertebra (DBGI 69 h) in right lateral view; (b) middle cervical vertebra (DBGI 69G1) in right lateral view; (c) anterior cervical vertebra (DBGI 165) in right lateral view; (d) anterior cervical vertebra (DBGI 69G2) in right lateral view; (e) atlas (DBGI 5I) in anterior view; (f) atlas (DBGI 5I) in right lateral view; (g) posterior cervical vertebra (DBGI 95) in right lateral view; (h) posterior cervical vertebra (DBGI 19 A) in right lateral view; (i) posterior cervical vertebra (DBGI 19 A) in ventral view; (j) middle cervical vertebra (DBGI 38) in right lateral view; (k) middle cervical vertebra (DBGI 38) in dorsal view; (l) middle cervical vertebra in posterior view; (m) middle cervical vertebra (DBGI 38) in left lateral view; (n) right anterior cervical rib (DBGI 5D) in medial view; (o) right anterior cervical rib (DBGI 28 A) in medial view; (p) right anterior-middle cervical rib (DBGI 95 C) in medial view; (q) right middle cervical rib (DBGI 45 F) in dorsal view; (r) right middle cervical rib (DBGI 95 A) in dorsal view; (s) left anterior cervical rib (DBGI 95B) in lateral view; (t) left middle cervical rib (DBGI 95 H) in lateral view; (u) left middle cervical rib (DBGI 95D) in dorsal view; (v) right posterior cervical rib (DBGI 10) in dorsal view. A plus sign (+) indicates a diagnostic character for Mierasaurus bobyoungi gen. et sp. nov. An asterisk (*) indicates an autapomorphy of Mierasaurus bobyoungi gen. et sp. nov. (© Fundación Conjunto Paleontológico de Teruel-Dinópolis) in Adobe Illustrator CS5 (www.adobe.com/es/products/illustrator.html).

[Because this paper is in Nature’s Scientific Reports, it inexplicably has a big chunk of manuscript chopped out of the middle, supplied separately, not formatted properly, and for all we know not peer-reviewed. This includes such minor details as the specimen numbers of the elements that make up the holotype, and the measurements. Note to self: rant about how objectively inferior Scientific Reports is to PeerJ and PLOS ONE some time.]

Anyway, this is a nice specimen represented by lots of decent material, including plenty of presacral vertebrae, which is great.

But here’s where it gets weird. Until now, Turiasauria has been an exclusively European clade. Just like Diplodocidae used to be an exclusively North American clade until Tornieria turned up, and Dicraeosauridae used to be an exclusively Gondwanan clade until Suuwassea turned out to be a dicraeosaur, and so on.

I mentioned this in an email to Matt. His initial take was:

There is a semi-tongue-in-cheek biogeography “law” that states “Everything is everywhere, and the environment selects”.

It is kinda blowing my mind that so many taxa were shared between North America, Europe, and Africa in the Late Jurassic and yet we don’t see any turiasaurs in North America until the Cretaceous. I wonder if they are there in the Morrison and just not recognized — either some of the undescribed or undiscovered northern-Morrison weirdness, or currently lumped in with Camarasaurus.

I responded “That’s one read. Another is that we’re seeing convergence on similar eco-niches within widely different clades, and our analyses are not figuring this out.”

What I mean is this: what if our “Brachiosauridae” clade is really just a collection of not-closely-related taxa in the tall-shouldered very-high-browser ecological niche? And what if our “Dicraeosauridae” clade is just a collection of short-necked grazers, with independent evolutionary origins, but all converging on morphology that suits the same lifestyle?

And that is the thought that is currently freaking me out.

Royo-Torres et al. 2107, fig. 4. The postcranial skeleton (UMNH.VP.26004) of Mierasaurus bobyoungi gen. nov, sp. nov. with the following elements: (a) anterior dorsal vertebra (DBGI 54 A) in posterior view; (b) anterior dorsal vertebra (DBGI 54 A) in anteroventral view; (c) neural arch of a middle dorsal vertebra (DBGI 37) in right anterolateral view; (d) posterior neural arch of a dorsal vertebra (DBGI 19 A) in posterior view; (e) anterior dorsal vertebra (DBGI 16) in right lateral view; (f) anterior dorsal vertebra (DBGI 16) in posterior view; (g) posterior dorsal vertebra (DBGI 16) in anterior view; (h,i) posterior dorsal vertebra (DBGI 100NA 1) in anterior view; (j,k) posterior dorsal vertebra (DBGI 100NA 1) in posterior view; (l) posterior dorsal vertebra (DBGI 100NA 1) in left lateral view; (m) middle dorsal vertebra (DBGI 11) in anterior view; (n) centrum of a posterior dorsal vertebra (DBGI 24B) in ventral view; (o) centrum of a posterior dorsal vertebra (DBGI 24B) in anterior view; (p) centrum of a posterior dorsal vertebra (DBGI 192) in ventral view; (q) anterior-middle caudal vertebra (DBGI 23B) in anterior view; (r) anterior-middle caudal vertebra (DBGI 23B) in right lateral view; (s) posterior neural arch of a posterior caudal vertebra (DBGI 48) in left lateral view; (t) posterior caudal vertebra (DBGI 21) in anterior view; (u) posterior caudal vertebra (DBGI 21) in right lateral view; (v) distal caudal vertebra (DBI 37-34-529) in right lateral view; (W) anterior caudal vertebra (DBGI 192) in posterior view. For abbreviations see supplementary information. (i), (k) and (l) were drafted by R.R.T. (© Fundación Conjunto Paleontológico de Teruel-Dinópolis) in Adobe Illustrator CS5 (www.adobe.com/es/products/illustrator.html).

When I mentioned this possibility to Matt, he shared my existential terror:

What haunts me is this: we know from mammals and extant reptiles that morphological analyses suck. Laurasian moles, African moles, and Australian moles all look the same, despite evolving from very different ancestors. Ditto wolves and thylacines, horses and litopterns, etc.

Matt reminded of a paper we’ve talked about before (Losos et al. 1998), showing that this is exactly what happens with Caribbean anole lizards. Each island has forms that live on the ground, on the trunks of trees, and on branches. Phylogenetic analyses based on morphology put all the ground-livers together, ditto for trunk-climbers, ditto for branch-climbers. But molecular analyses show that each island was colonized once and the ground, trunk, and branch forms evolved separately for each island.

What if “turiasaur”, “brachiosaur”, and “titanosaur” are the sauropod equivalents? For “Caribbean island” read “continent”; for “lizard species”, read “sauropod clade”.

Will we ever know?

Matt is hopeful that we will. He’s confident that in time, we’ll get molecular analyses of dinosaur relationships — that it’s just a matter of time and cleverness. When that happens, things could be upended bigtime.

References

 

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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.

Just got the APP new issue alert and there are three papers that I think readers of this blog will find particularly interesting:

That’s all for now, just popping in to let people know about these things.

Here’s a dorsal vertebra of Camarasaurus in anterior view (from Ostrom & McIntosh 1966, modified by Wilson & Sereno 1998). It is one of the most disturbing things I have ever seen in a sauropod. It makes my skin crawl.

Here’s why: the centrum and the thing we habitually call the ‘neural arch’ aren’t fully fused, and as this modified version makes clear, the ‘neural arch’ is neither neural nor an arch. Instead of being bounded ventrally by the centrum and dorsally and laterally by the neural arch, the neural canal lies entirely below the synchondrosis between the not-really-an-arch and the centrum.

Why?! WHY WOULD YOU DO THAT, CAMARASAURUS? This is not ‘Nam. This is basic vertebral architecture. There are rules.

Look at c6 of Apatosaurus CM 555 here, behaving as all good vertebrae ought to. Neural arch be archin’, as the kids say.

And if you are seeking solace in the thought that maybe the artist just drew that Cam dorsal incorrectly, forget it. I’ve been to Yale and examined the original specimen. I’ve seen things, man!

Camarasaurus isn’t the only pervert around here. Check this out:

Unfused neural arch of a caudal vertebra of a juvenile Alamosaurus from Big Bend. And I mean, this is a neural arch. This may be the most neural of all neural arches, in that it contains the entire neural canal. It’s more of a neural…ring, I guess. That’s right, this Alamosaurus caudal is batting for the opposite team from the Cam dorsal above. And it’s a team that neither you nor I play on, because we have well-behaved normal-ass vertebrae with neural arches that actually arch, and then stop, like God and Richard Owen intended.

Scientifically, my question about these vertebrae is: well, that is, I mean to say, what!? I think they have damaged me in some fundamental way.

If you have anything more intelligent to add (or even less intelligent – consider the gauntlet thrown down!), the comment thread is open.

References

  • Ostrom, John H., and John S. McIntosh. 1966. Marsh’s Dinosaurs. Yale University Press, New Haven and London. 388 pages including 65 absurdly beautiful plates.
  • Wilson, J. A. and Paul C. Sereno. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.

Anterior view. Dorsal is to the upper right. The neural spine and left transverse process are missing.

Here’s a closeup of the condyle. The outer layer of cortical bone is gone, allowing a glimpse of the pneumatic chambers inside the vert. The erosion of the condyle was probably inflicted post-excavation by relatively unskilled WPA workers, whose prep tools were limited to chisels, penknives, and sandpaper. Because the bones from the Kenton localities are roughly the same color as the matrix, the preparators sometimes did not realize that they were sanding into the bones until the internal structure was revealed. Bad for the completeness of this specimen, but good for pneumaticity junkies like me, because this baby is too big to be scanned by any but the largest industrial CT machines.

For other posts on the giant Oklahoma apatosaur, see:

jvp-fig-12

Fig. 14. Vertebrae of Pleurocoelus and other juvenile sauropods. in right lateral view. A-C. Cervical vertebrae. A. Pleurocoelus nanus (USNM 5678, redrawn fromLull1911b: pl. 15). B. Apatosaurus sp. (OMNH 1251, redrawn from Carpenter &McIntosh 1994: fig. 17.1). C. Camarasaurus sp. (CM 578, redrawn from Carpenter & McIntosh 1994: fig. 17.1). D-G. Dorsal vertebrae. D. Pleurocoelus nanus (USNM 4968, re- drawn from Lull 1911b: pl. 15). E. Eucamerotus foxi (BMNH R2524, redrawn from Blows 1995: fig. 2). F. Dorsal vertebra referred to Pleurocoelus sp. (UMNH VP900, redrawn from DeCourten 1991: fig. 6). G. Apatosaurus sp. (OMNH 1217, redrawn from Carpenter & McIntosh 1994: fig. 17.2). H-I. Sacral vertebrae. H. Pleurocoelus nanus (USNM 4946, redrawn from Lull 1911b: pl. 15). I. Camarasaurus sp. (CM 578, redrawn from Carpenter & McIntosh 1994: fig. 17.2). In general, vertebrae of juvenile sauropods are characterized by large pneumatic fossae, so this feature is not autapomorphic for Pleurocoelus and is not diagnostic at the genus, or even family, level. Scale bars are 10 cm. (Wedel et al. 2000b: fig. 14)

The question of whether sauropod cervicals got longer through ontogeny came up in the comment thread on Mike’s “How horrifying was the neck of Barosaurus?” post, and rather than bury this as a comment, I’m promoting it to a post of its own.

The short answer is, yeah, in most sauropods, and maybe all, the cervical vertebrae did lengthen over ontogeny. This is obvious from looking at the vertebrae of very young (dog-sized) sauropods and comparing them to those of adults. If you want it quantified for two well-known taxa, fortunately that work was published 16 years ago – I ran the numbers for Apatosaurus and Camarasaurus to see if it was plausible for Sauroposeidon to be synonymous with Pleurocoelus, which was a real concern back in the late ’90s (the answer is a resounding ‘no’). From Wedel et al. (2000b: pp. 368-369):

Despite the inadequacies of the type material of Pleurocoelus, and the uncertainties involved with referred material, the genus can be distinguished from Brachiosaurus and Sauroposeidon, even considering ontogenetic variation. The cervical vertebrae of Pleurocoelus are uniformly short, with a maximum EI of only 2.4 in all of the Arundel material (Table 4). For a juvenile cervical of these proportions to develop into an elongate cervical comparable to those of Sauroposeidon, the length of the centrum would have to increase by more than 100% relative to its diameter. Comparisons to taxa whose ontogenetic development can be estimated suggest much more modest increases in length.

Carpenter & McIntosh (1994) described cervical vertebrae from juvenile individuals of Apatosaurus and Camarasaurus. Measurements and proportions of cervical vertebrae from adults and juveniles of each genus are given in Table 4. The vertebrae from juvenile specimens of Apatosaurus have an average EI 2.0. Vertebrae from adult specimens of Apatosaurus excelsus and A. louisae show an average EI of 2.7, with an upper limit of 3.3. If the juvenile vertebrae are typical for Apatosaurus, they suggest that Apatosaurus vertebrae lengthened by 35 to 65% relative to centrum diameter in the course of development.

The vertebrae from juvenile specimens of Camarasaurus have an average EI of 1.8 and a maximum of 2.3. The relatively long-necked Camarasaurus lewisi is represented by a single skeleton, whereas the shorter-necked C. grandis, C. lentus, and C. supremus are each represented by several specimens (McIntosh, Miller, et al. 1996), and it is likely that the juvenile individuals of Camarasaurus belong to one of the latter species. In AMNH 5761, referred to C. supremus, the average EI of the cervical vertebrae is 2.4, with a maximum of 3.5. These ratios represent an increase in length relative to diameter of 30 to 50% over the juvenile Camarasaurus.

If the ontogenetic changes in EI observed in Apatosaurus and Camarasaurus are typical for sauropods, then it is very unlikely that Pleurocoelus could have achieved the distinctive vertebral proportions of either Brachiosaurus or Sauroposeidon.

apatosaurus-cm-555-c6-centrum-and-arch-united

C6 of Apatosaurus CM 555 – despite having an unfused neural arch and cervical ribs, the centrum proportions are about the same as in an adult.

A few things about this:

  1. From what I’ve seen, the elongation of the individual vertebrae over ontogeny seems to be complete by the time sauropods are 1/2 to 2/3 of adult size. I get this from looking at mid-sized subadults like CM 555 and the hordes of similar individuals at BYU, the Museum of Western Colorado, and other places. So to get to the question posed in the comment thread on Mike’s giant Baro post – from what I’ve seen (anecdata), a giant, Supersaurus-class Barosaurus would not necessarily have a proportionally longer neck than AMNH 6341. It might have a proportionally longer neck, I just haven’t seen anything yet that strongly suggests that. More work needed.
  2. Juvenile sauropod cervicals are not only shorter than those of adults, they also have less complex pneumatic morphology. That was the point of the figure at the top of the post. But that very simple generalization is about all we know so far – this is an area that could use a LOT more work.
  3. I’ve complained before about papers mostly being remember for one thing, even if they say many things. This is the canonical example – no-one ever seems to remember the vertebrae-elongating-over-ontogeny stuff from Wedel et al. (2000b). Maybe that’s an argument for breaking up long, kitchen-sink papers into two or more separate publications?

Reference

Wedel, M.J., Cifelli, R.L., and Sanders, R.K. 2000b. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45:343-388.

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