Is the French Monster the biggest dinosaur ever?

Earlier you may have heard of a truly colossal sauropod species known as the French Monster. First it appeared to be a titanosaur, though now it looks to be a basal somphospondyl, along the same lines as Chubutisaurus and Paluxysaurus.

It's a massive creature no doubt, but one thing severely lacking from the announcements of the finds several years ago (besides a description paper and a name!) was a set of proper measurements for the bones. We do have some good pics though, from the dig site in Angeac-Charente, which is apparently wine country. It's tempting to think that fossil-rich soils make for top-quality grapes... lots of minerals there. And tannins... look at how dark those bones are, surely from all the tannins, it must be. Most significant were two femurs from different individuals, one of which was well-photographed and appeared to be about 2.2m long, the other being considerably larger. Below you see the smaller one:

Photos of the larger femur, estimated at 2.6m, did not materialize. However there were some rare glimpses of other gigantic bits.

Some of the biggest caudal vertebrae ever found, and quite possibly the biggest toe bone ever found (the darker bone near the center).

Then we have this gem, which it the lower end of either a tibia or a very worn-down femur. Again, huge.

The foot claws are just enormous. This one is as big as a sewing machine.

One toe bone from this sauropod (right) is more massive than the whole femur of a theropod found at the same site (left).

There are also some teeth from the site, with the same black mineralization as the first femur, and encrusted with some sort of comglomerate. They look similar to brachiosaur teeth, which is not surprising given that the unique features of the femur put it closest to the Chubutisauridae, which are only a couple steps removed from brachiosaurs.

We also know that a cast was made of the 2.2m femur. For some years, little more was known.

Gunnar Bivens gave me this link to some sources: dml.cmnh.org/2017Apr/msg00032.… which include information on the French Monster. Not only do they verify the size of the 2.2m femur known, as well as the other materials, but they also verify the estimate of the larger femur at 2.6m long when complete - surpassing the femur of Argentinosaurus.

Given that the French Monster appears to cluster closest to Paluxysaurus and Sauroposeidon and shares several diagnostic femur features in common with both of them (there is a juvenile Cloverly Formation femur from the latter), a good place to start when scaling the French Monster is the already existing Paluxysaurus skeletal from Steve O'Connor:

Assuming you use the Paluxysaurus proportions as seen here, and a GDI based on the mounted skeleton, the "adult" Sauroposeidon from Oklahoma would scale up to 26.9m 47.5 tonnes, as per Franoys. The same model yields dimensions for the two French Monster specimens known from the 2.2m and 2.6m femurs at [28.5m and 56.5 tonnes] and [33.5m and 85 tonnes] respectively. Yes, I said 85 tonnes. That's up in Argentinosaurus territory, and for a dinosaur that almost certainly had a slimmer rib cage - which would require it to be a hugely tall animal, and in lateral view its slimmer torso would actually have to look bigger and deeper than that of Argentinosaurus to get the same volume and mass.

Those are impressive sizes. Though I suspect they may be a bit conservative, as it's unlikely that an adult Sauroposeidon had the same proportions as Paluxysaurus (though the juvenile Cloverly Sauroposeidons apparently did). I would expect more elongation in the neck and tail for the "adult" Sauroposeidon, and the four cervicals we have were likely not the longest ones in the neck. Similarly, the French monster would likely top those estimates based on likely neck elongation assuming its juvenile form was something like the juvenile Sauroposeidons from Cloverly.

I would estimate Sauroposeidon somewhere around 28-30m, and the two French Monsters known from femurs at around 33m and 36m respectively. But even these aren't the biggest specimens of the French Monster. The real whopper stretches the limits of credibility. There is a huge rib pictured on one of those French websites that's AT LEAST as long as 4 people! www.bulbintown.com/projects/le… Am I seeing this right? This would have to be some kind of record breaker, even bigger than the larger femur specimen. Think about it - the larger ribs in a sauropod typically were in the same length range as the femur, a bit more when you account for their curve length. But if a sauropod's femur is 2.6m long, its unlikely that a 4m+ rib would come from the same specimen. So we have a third gigantic individual, which would have easily outclassed the other two.

DAAAAAAAMN that's a big rib. That's 5 people lying next to it, but the guy at the top may be next to a dorsal vertebra as the rib head seems to terminate further down. At the bottom, the end is broken off! So there was even more...

This is great news. Now we have a basal somphospondyl to rival Argentinosaurus. Even if you ignore the rib specimen and go based only on the individual that provided the larger of the two femurs, 33.5m and 85 tonnes (?!?) for a chubutisaur is no joke.

And that crazy-huge rib... that thing must be 6m long? Admittedly it's pretty flattened from millions of years of being buried under tons of rock, but even when uncrushed and in its natural curve, that's at least a 4m-deep rib cage in strictly linear side-view dimensions. I know there are a lot of issues with scaling sauropods off of just rib pieces, but keep in mind, this rib looks to be 6m long and is still missing the bottom end! So conservatively at 4m uncrushed and articulated, what does that come out to, a 112 foot or 36m animal using my B. alithorax as a model (it has a similarly long torso), but the neck would be a lot longer in Sauroposeidon or the French Monster...

... so using Steve O'Connor's Paluxysaurus skeletal is a better model (more elongated neck plus proportionally shallower ribcage), then we have a total length/longest rib length ratio of 10.24, so we get a 41m animal! This means it's about 1.22 times the length of Franoys' estimate for the larger femur specimen (remember, that's still a conservative estimate). Cubing that for all 3 dimensions, we get 1.81 times the volume of that specimen, and thus 1.51 times the mass.  = 154 tonnes. THIS IS INSANE! The Oklahoma apatosaur and the newly legendary BYU Barosaurus specimens might as well roll up and cry. Move over, boring diplodocid fern-slugs. Macronarians have the crown once again!

Folks, we may have the biggest dinosaur ever here. I'm not claiming it "must" be 154 tonnes, it may not be much more than 100-110 tonnes depending on how these animals grew allometrically. But that's still in Puertasaurus/Mexican Alamosaurus/biggest individual of Chubut Monster territory. And the 41m length exceeds all of these animals, and is still only based on using the Paluxysaurus skeletal as a model, still ignoring how much distal material is missing from the rib, and still scaling up from Franoys' conservative estimate for the larger French Monster Femur. With better photos we may be able to bring down the size, but for now... WOW. 41m and possibly in excess of McNeill Alexander's (flawed) "upper limit" for sauropod masses. I'm not joking, this could be the find of the century.

At least one of these French Monsters is a real record crusher, probably the individual with that huge rib (assuming it's not a petrified tree, which is unlikely given all the attention it's getting from the dig team in that photo, plus its apparently rib-like proximal end and close proximity to an obvious distal rib fragment next door). There are no pictures of the rib fully prepared, or of the 2.6m femur. But we know how to scale them so I'm confident this animal could have gotten bigger than Argentinosaurus and perhaps even any of the other mega-titanosaurs.

For now here is an image of a museum display for the smallest of the three French Monster specimens examined here, the 2.2m complete femur, with a fibula from the same individual. Even this animal is huge, and it's dwarfed by the two bigger ones. And chubutisaurs actually had a pretty low femur-to-body length ratio, which means they outclassed most sauropods in total body length, for any given femur size.

And now imagine one twice this size, with that 4m rib... just to keep one thing in mind, a 4m rib also blows the ribs of Supersaurus (the prior record-holder for deepest ribcage), the Potter Creek brachiosaur, and "Huanghetitan" ruyangensis clear out of the ballpark. Using Paluxysaurus neck proportions, the giant rib individual also would have beat out Supersaurus, Daxiatitan, Yunmenglong, and "Mamenchisaurus" sinocanadorum for neck length (and obviously Sauroposeidon as well). And a 4m rib is a conservative estimate for that photograph, not accounting for the broken lower end! You have not even begun to see the biggest dinosaurs, it seems to say.

Was the French Monster the biggest? Did some individuals of the mega-titanosaurs get larger? Dump your comments below, but now I think you're pretty clear on where I stand. There are already plenty of pics here for the limb and tail parts of smaller individuals, which are unquestionably already in super-sauropod range. Unless that rib turns out to be anything other than a rib (and if a rib that thick ends up being a cervical rib rather than a dorsal rib, that's even scarier), we are looking at the new biggest dinosaur. Full stop.