Retro vs Modern #11: Brontosaurus excelsus

Discovered in the Western United States during the 1870s, in the early years of the Bone Wars, Brontosaurus excelsus was one of the most complete sauropod dinosaurs known at the time.


In the early 1900s the genus name Brontosaurus was declared invalid and it was reclassified as a species of the very-closely-related Apatosaurus, renaming it to Apatosaurus excelsus – but this change took decades to be recognized outside of scientific literature, and by that time the “Brontosaurus” name had already stuck in pop culture. With the prominence of the name’s use in early 20th century museum displays and its charismatic meaning of “thunder lizard”, it rapidly became one of the most famous and recognizable dinosaurs to the general public.

Like most sauropods of the time Brontosaurus was generally portrayed as a large bulky lizard-like creature with an arched back, thick elephant-like legs, and a long dragging tail. Opinions on its neck posture varied over time, ranging from low-slung and horizontal to highly vertical, and it was commonly depicted wallowing lazily half-submerged in swamps due to sometimes being considered too big to easily support its own weight on land.

And along with spending most of the century with the wrong name, Brontosaurus also spent most of it with the wrong head. While a slender Diplodocus-like skull had been found close to the rest of an Apatosaurus skeleton in the early 1900s, it was rejected by some paleontologists and both Brontosaurus and Apatosaurus were instead given boxy Camarasaurus-like skulls that were thought to be more fitting for such big beefy-necked sauropods.


The Dinosaur Renaissance in the late 20th century completely revolutionized the understanding of sauropods and their biology. They were dragged out of the swamps and put properly back onto dry land, reinterpreted as active animals with their long tails held up off the ground and bird-like air sacs lightening their bodies.

The correct skull shape for Brontosaurus and Apatosaurus was also finally recognized in the late 1970s, and during the the 1990s and early 2000s a very horizontal neck posture became the standard depiction for this type of diplodocid sauropod. But by the 2010s this was being argued as biomechanically wrong – animals usually hold their necks at a much higher angle than the bones alone would suggest, and sauropods almost certainly did the same.

And then in 2015 the name Brontosaurus was reinstated as valid after all, in a massively thorough analysis of the diplodocid family that found enough physical differences between Brontosaurus and Apatosaurus to justify them both being separate genera again.

So our modern view of Brontosaurus excelsus (formerly known as Apatosaurus excelsus, even-more-formerly known as Brontosaurus excelsus) is a large sauropod that grew to around 22m long (72′). It lived during the Late Jurassic, about 156-146 million years ago, at a time when the supercontinent of Pangaea was starting to break apart and much of Western North America was a warm and semi-arid “Jurassic savanna” environment.

Its head was small and fairly delicate, similar to that of Diplodocus, atop a wide deep neck with chunky vertebrae. It had a deep chest and stout limbs, with its hands being semi-tubular pillars with a single “thumb” claw, and its feet having three large curved claws. Its tail made up over half its body length and was relatively slender, tapering into a long whip-like tip that may have been able to make loud cracking sounds like a bullwhip.

It was probably capable of briefly rearing up to reach higher vegetation, and small juveniles may even have been able to run on just their hind legs.

Soft tissue impressions from other diplodocids show keratinous spines running along the top of their tails, and complex variation in the sizes and shapes of scales across different parts of their bodies – so Brontosaurus may have been similarly ornamented.

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.