Zby atlanticus, a sauropod dinosaur from the Late Jurassic of Portugal (~156-151 mya). While its genus name might look like a keyboard smash, it was actually named after the Russian-French paleontologist Georges Zbyszewski, who spent much of his career studying Portuguese fossils.

(As for how to pronounce it, according to the original paper it’s “zee-bee”.)

It was a close relative of Turiasaurus, the largest dinosaur currently known from Europe – and although Zby itself wasn’t quite so enormous it was still pretty big, probably measuring somewhere around 15-19m long (49′2″-62′4″).

In fact, all the sauropods known from Late Jurassic Portugal seem to have grown to very large adult sizes. The complete lack of medium or small forms suggests that other types of herbivorous dinosaurs may have dominated the region’s lower-browsing niches at the time.

Unsolved Paleo Mysteries Month #18 – The Biggest Beefy Boys

In 1878, during the Bone Wars of American paleontology, Edward Drinker Cope published a description of a partial sauropod vertebra and femur from the Late Jurassic of Colorado (~150 mya). He classified it as a new species of the diplodocoid genus Amphicoelias (which he had named earlier that same year), designating it as Amphicoelias fragillimus in reference to the bone’s poor condition and incredibly fragile structure.

But what set this fragmentary find apart was its sheer size. The partial back vertebra measured around 1.5m tall (5′), with estimates of its full height anywhere up to 2.7m (8′10″) – twice the size of the same bone in Diplodocus, and far larger than anything else known.

Obviously its very difficult to accurately estimate the full body size of an animal from a single broken bone, but plenty of attempts have been made anyway, producing lengths of up to 60m (197′). For comparison, the largest living animal the blue whale reaches lengths of around 33m (108′).

Around the time of Cope’s death in 1897, his massive fossil collection was sent to the American Museum of Natural History, and the A. fragillimus vertebra was entered into their catalog

Only to vanish, never to be seen again.

Multiple searches through the collection have found no trace of it, and there’s speculation that at some point the fragile bone may have crumbled entirely into pieces and been thrown away. No other material of A. fragillimus has ever been found in the ~140 years since its description, despite searches of the area where it was originally discovered, leading to claims of the entire specimen being a hoax – suggestions that Cope exaggerated or typoed his measurements in his rush to outdo his rival Othniel Charles Marsh.

Without that paleontological holy grail of finding the lost fossil or a new specimen, we just don’t know how big that bone truly was, or whether A. fragillimus was a living kaiju or a much more “normal-sized” sauropod. There’s even been some speculation of it being proportioned more like a rebbachisaur, with tall “sailback” vertebrae.


In a surprise plot twist, there is another.

An absolutely enormous neck vertebra hints at the existence of other gigantic mega-sauropods. We still don’t have enough remains to know what the heck was going on with these animals – how did they even manage to get so huge? were they rare individuals who lived long enough to grow into “super-adults”? – but the prospect of perhaps one day finally validating A. fragillimus’ enormous size is exciting.

My version of Amphicoelias fragillimus here works out to about 50m long (164′), although it might be closer to 60m long with a more horizontal neck posture. Its proportions are mainly based on a mixture of Diplodocus, Supersaurus, and Barosaurus, with slightly taller neural spines raising its back profile a bit and some big fat deposits thickening up its tail.


Aaand we’re back to normal updates with a fully working computer again!

Let’s properly start off this year’s art pieces with a particularly weird sauropod dinosaur. This is Brachytrachelopan, known from Argentina at the very end of the Jurassic (~152-145 mya).

A member of the dicraeosaurids, it was a close relative of the spiky-necked Amargasaurus and was roughly the same size at about 10m long (32′9″) – but it also had the shortest neck of any known sauropod, suggesting it was specialized for a completely different diet. It may have been a sort of “iguanodont-mimic”, adapted to a low browsing niche, since actual iguanodonts were absent from its ecosystem.

I’ve given this one a little bit of speculative bristly fuzz, because I can. While all currently known sauropod skin impressions show scales, we don’t have full-body coverage and fuzz was almost certainly present in their ancestors – and both types of integument can also exist on the same animal in the same places.

Also I just like the idea of sauropods with manes and beards.