Amargasaurus

Amargasaurus cazaui was a sauropod dinosaur with a very distinctive-looking skeleton, sporting a double row of long bony spines along its neck and back. It lived in what is now Argentina during the Early Cretaceous, about 129-122 million years ago, and was fairly small compared to many other sauropods, reaching about 10m in length (~33′) with a proportionally short neck compared to its body size.

And despite being known from fairly complete skeletal remains there’s still a lot we don’t know about this dinosaur – especially what was actually going on with those vertebral spines. While it’s sometimes been depicted with skin sails over the spines, for the last couple of decades the general opinion has trended towards them being more likely to have been covered by spiky keratinous horn-like sheaths.

But recently that’s been brought back into question. A detailed study of the microscopic bone structure of Amargasaurus‘ spines shows no evidence for keratin attachment and instead found textures associated with skin coverings, along with an extensive web of ligaments connecting the spines to each other along each row.

So maybe it had big flashy sails after all!

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.


1900s-1970s

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.


2020s

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.

Retro vs Modern #10: Plateosaurus trossingensis

First discovered in southeast Germany in the 1930s, Plateosaurus was only the fifth non-avian dinosaur known to science – but its fossils were fragmentary and poorly understood until the early 20th century, when large bonebeds full of much better specimens began to be excavated.


1910s-1970s

Between the 1910s and 1930s around 80 near-complete skeletons of Plateosaurus were found in two German quarries, quickly making it one of the most abundant and best known dinosaur species of the time. Although it had previously been classified as a theropod dinosaur, in the 1920s the more complete material allowed it to be properly identified as a “prosauropod“, an early herbivorous relative of the giant sauropods

Like many bipedal dinosaurs during this period Plateosaurus was generally interpreted as having an upright kangaroo-like posture with a dragging tail – although some paleontologists were arguing for it having a sprawling quadrupedal lizard-like stance as late as the mid-1930s.


1980s

Unfortunately much of the German fossil material was destroyed during World War II bombing raids, and interest in Plateosaurus didn’t pick up again until the time of the Dinosaur Renaissance when a third major fossil site was discovered in Switzerland during the 1970s.

Plateosaurus was reinterpreted with a horizontal body posture and fully upright limbs. As an early member of the sauropodomorph lineage it was often depicted as a transitional form between bipedal ancestral dinosaurs and the later quadrupedal sauropods, thought to primarily walk on all fours but also able to run on its hind legs like a hadrosaur – although some studies instead concluded it was fully quadrupedal with a downwards-curling tail that made bipedal movement impossible.

The large numbers of skeletons found together were considered to represent evidence for herding behavior, with groups of Plateosaurus being caught in catastrophic mudflows all at once.


2020s

Extensive biomechanical studies in the 2000s and early 2010s clarified what sort of posture Plateosaurus was really capable of. It was found to be completely unable to position its arms in a quadrupedal stance, and so was actually purely bipedal – and skeletons that had been mounted in the quadrupedal position had needed many of their joints to be completely dislocated to achieve the pose!

A huge number of different Plateosaurus species had been named over the genus’ nearly-200-years of history, too, creating a confusing mess of dubious and invalid names. These were all finally revised in 2019 leaving just three valid species, with Plateosaurus trossingensis as the best known and the new type species.

We now know Plateosaurus lived across central and northern Europe during the Late Triassic, around 214-204 million years ago, at a time when the region had a subtropical climate. It had a small head on a long flexible neck, with teeth convergently resembling those of modern iguanas suggesting it was probably primarily herbivorous (with possible opportunistic omnivory). Its arms were proportionally short for a prosauropod but were well-adapted for grasping, with large claws that may have been used to dig up roots and tear down branches

It had a rapid growth rate and bird-like lungs and air sacs that suggest it was warm-blooded, and different individuals showed an unusually high amount of variation in adult size and age of maturity. Some appear to have been fully grown at about 5m long (~16′) and as young as 12 years old, while others reached 10m long (~33′), and were still growing at 27 years old.

The bonebeds are no longer thought to represent mass mortalities of herds, but instead were probably a scenario more similar to the La Brea Tar Pits – mud-miring traps that smaller lighter animals could escape from but larger individuals became stuck and died.

No prosauropod skin impressions have been found yet, so it’s still unknown whether Plateosaurus was scaly like later sauropods or if it had some degree of protofeather hair-like fuzz.

Atlasaurus

Sauropod dinosaurs were just generally weird animals, but there’s something… not quite right about Atlasaurus imelakei.

Named after the Atlas Mountains of Morocco where its fossil remains were discovered, Atlasaurus lived during the mid-Jurassic period, around 168-165 million years ago. While it wasn’t the strangestlooking sauropod by any means, compared to other species its body proportions still show a particularly bizarre combination of features, with a slightly bigger head, unusually short neck, and very long slender legs that made up nearly half of its 9m height (29’6″).

It’s sort of the uncanny valley of sauropods. Everything about it is just a tiny bit wrong.

A photograph of an Atlasaurus model. Its been reconstructed very skinny, which only serve to emphasize its weird proportions.
And more shrinkwrapped depictions really don’t help with that. [image source]

Its tall shoulders and sloping back resemble the body plan of brachiosaurids so closely that it was initially thought to be an early member of that group, but more recent studies suggest it may have been part of an earlier evolutionary branch of sauropods known as the turiasaurs – which would mean its brachiosaur-like shape was actually the result of convergent evolution.

But what was it doing with such weird proportions?

…We really don’t know. Other short-necked sauropods seem to have been adapted for feeding on lower vegetation only a couple of meters off the ground, but Atlasaurus’ leggy build would have made it a high browser like the brachiosaurids it was mimicking. Its long legs may also have allowed it to move faster, or given it some advantage navigating over rough terrain, but since no other sauropod ever seemed to evolve this way it must have been doing something particularly unique.

Or perhaps it was just an evolutionary fluke. Maybe part of a lineage that had started adapting to short-necked low browsing, then moved back towards the high browsing niche – and happened to end up lengthening their legs instead of their necks to get the necessary height back.

Kaijutitan

Originating from Japanese monster movies like Godzilla, the word “kaiju” is now often used to refer to giant creatures in general – and so it was only a matter of time before a huge sauropod dinosaur was named after the concept.

Kaijutitan maui* was a titanosaur living in Argentina during the Late Cretaceous, about 89-86 million years ago. It’s only known from fragmentary remains, so its full size is difficult to estimate, but it was probably somewhere in the region of 20m long (66′). Nowhere close to the largest sauropod, but possibly one of the heaviest since it does seem to have been rather chunkily built, with stout limbs and an estimated weight of 40-60 tonnes (44-66 US tons).

* Not named for the Polynesian hero, apparently, but for the initials of the Museo Argentino Urquiza.

Island Weirdness #05 – Magyarosaurus dacus

At the very end of the Cretaceous period, between about 72 and 66 million years ago, tectonic uplift from the start of the formation of the Alps created an island in the area corresponding to modern-day Romania.

Known as Hațeg Island, after the region where fossils of the native species were found, it was similar in size to Hispaniola and was surrounded by deeper waters than most of the other European archipelago islands.

Magyarosaurus here was was a titanosaur living on this island, and was one of the smallest known of all sauropod dinosaurs at just 6m long (19’8″). Much of that length would have been in its neck and tail, and its body was only actually about the size of a horse.

Like some other titanosaurs it had bony osteoderm armor along its back, although since only one isolated piece has been found the exact arrangement isn’t known.

Discovered by Franz Nopsca (the gay Transylvanian baron-paleobiologist-spy), in the early 1900s, it was one of the first dinosaurs proposed as an example of insular dwarfism. Later researchers disagreed with this hypothesis, suggesting instead that the Magyarosaurus fossils were just juveniles – and it wasn’t until 2010 that studies of bone microstructure proved that these miniature sauropods really were fully grown adults.

Island Weirdness #02 – Europasaurus holgeri

Sauropod dinosaurs are mainly known for being enormous, and so even some of the smallest members of the group were actually quite large compared to modern animals.

Europasaurus was an early brachiosaurid that lived during the Late Jurassic, about 154 million years ago, on a small island in the Lower Saxony region of northwestern Germany. It was an example of insular dwarfism in a sauropod, only growing to around 6.2m in length (~20′) – less than half the size of some of its other relatives.

A layer of rock just above the deposit of Europasaurus fossils also gives us a clue about their eventual fate. Footprints of large carnivorous theropods – bigger than the mini-sauropods themselves – suggest that at some point the sea level dropped and predators from the mainland were able to reach the island.

Since there were no large predators on the island before then,the small Europasaurus had no defenses against these new giant invaders. They very likely were literally eaten into extinction.

Island Weirdness #01

Islands are natural sites for evolutionary experiments. Their isolation and limited resources put a lot of selective pressure on their native species, often resulting in spectacular and unique adaptations. Big animals become small, small animals become big, and ecological niches can end up being filled in unexpected ways.

From the dodo becoming the first well-known example of human-caused extinction, to Darwin’s Galápagos finches being influential in the development of the theory of natural selection, to famous-but-endangered living examples like the kiwi and marine iguana, island species are fascinating and often fragile examples of how diverse life can get even in restricted conditions.

In fact, this theme ended up containing so many species I wanted to feature that I can’t possibly fit them all into just a single month. So, for the first time, a theme is going to need two months – with part 1 happening right now, and part 2 coming later this summer.


Thecodontosaurus antiquus

For much of the Mesozoic Europe was an archipelago of islands in a shallow tropical sea. During the Late Triassic, about 205-201 million years ago, some of the paleo-islands in this region existed around southern Wales and South West England, near the city of Bristol.

Thecodontosaurus was actually one of the first non-avian dinosaurs ever named by modern science, discovered in the mid 1830s – several years before the term “dinosaur” was even created to classify the “great ancient lizards”.

It was an early member of the herbivorous sauropodomorphs, the group that would eventually include the largest ever land animals. But unlike its enormous later cousins it was short-necked and bipedal, and was particularly small compared to other contemporary “prosauropods”, measuring only about 2m long (6′6″). This would make it one of the oldest known examples of insular dwarfism.

Zby

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.

Except

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.