Tag: dinosaur

April Fools 2022: The Aquatic Dinosaur That Wasn’t

So, Spinosaurus wasn’t technically the first known aquatic non-avian dinosaur.

That title instead temporarily went to Compsognathus corallestris.

While the idea that hadrosaurs and sauropods were wallowing swamp-dwellers had been completely abandoned at the start of the Dinosaur Renaissance, the new view of dinosaurs as active sophisticated animals led to a surprising aquatic hypothesis during the early days of this paleontological revolution.

A specimen of the small theropod Compsognathus discovered in southeastern France in the early 1970s was only the second skeleton ever found of this dinosaur, and came over a century after the first. It was initially thought to represent a new species since it was about 50% larger than the German specimen of Compsognathus longipes, and it seemed to have something very unusual going on with its hands – its forelimbs were somewhat poorly-preserved and distorted, and had traces of some sort of large fleshy structure around the hands that was interpreted as representing elongated three-fingered flippers used for swimming.

This wasn’t necessarily as ridiculous of an idea as it might sound. Compsognathus lived during the Late Jurassic, about 150 million years ago, at a time when Europe was a group of islands in a shallow tropical sea. A semiaquatic dinosaur specialized to swim and dive, hunting the abundant aquatic prey in its environment, and easily able to island-hop all around the European archipelago seemed at least somewhat plausible, and reconstructions of fin-handed C. corallestris even appeared in several popular dinosaur books of the time.

But it didn’t last.

Within just a few years doubt was being cast on this idea, and further studies of both known Compsognathus skeletons in the late 1970s and early 1980s concluded that C. corallestris was actually a fully-grown adult individual of the juvenile C. longipes. The French Compsognathus had normal-looking hands for its kind after all, with two large clawed fingers and a vestigial third finger, and the “flipper” impressions had just been ripples in the fossil slab.

For a long time after that the general view became that there just weren’t any aquatic non-avian dinosaurs at all – but more recent discoveries like the new Spinosaurus material and Halszkaraptor are starting to suggest that some of these animals were much more at home in the water than previously thought.

Something resembling Compsognathus corallestris might still surprise us in the future.

Retro vs Modern #23: Spinosaurus aegyptiacus

Spinosaurid teeth were first found in the 1820s in England, but were misidentified as belonging to crocodilians. It wasn’t until nearly a century later that Spinosaurus aegyptiacus was discovered and recognized as a dinosaur – and it would be another century after that before we really started to learn anything about it.

1910s

The first fossils of Spinosaurus were discovered in Egypt in the 1910s. With only a few fragments of its skeleton known it was an enigma right from the start, hinting at a large and very strange theropod dinosaur with crocodile-like teeth, an oddly-shaped lower jaw, and elongated neural spines on its vertebrae that seemed to be part of a huge sail.

A few possible extra fragments were found in the 1930s, but overall these few pieces were all that was known of Spinosaurus for a long time.

The fossils were kept in the Paleontological Museum in Munich, Germany,a building that was severely damaged during a bombing raid in World War II. Many important specimens were destroyed, including Spinosaurus, and only the published drawings and descriptions of the bones remained.

So for the next several decades Spinosaurus remained a very poorly-understood mystery. During this period it was generally depicted as a generic “carnosaur“, often modeled on something like Megalosaurus, in the standard-for-the-time tripod pose and with a Dimetrodon-like sail on its back.

Interestingly a 1930s skeletal reconstruction shows Spinosaurus with an unusually long torso and fairly short legs, details that are surprisingly modern despite the retro posture.

1990s

In the 1980s some partial snout bones from Niger were recognized as having similarities with the jaw of Spinosaurus. Around the same time the fairly complete skeleton of Baryonyx was discovered, and along with further spinosaurid discoveries in the mid-to-late 1990s a decent idea of what Spinosaurus might have looked like began to emerge.

It was reconstructed with a long kinked crocodilian-like snout, a ridged bony crest in front of its eyes, an S-curved neck, and large thumb claws on its hands – an interpretation that was heavily popularized by Jurassic Park III in the early 2000s, bringing this enigmatic dinosaur to public attention and portraying it as a fearsome super-predator bigger than Tyrannosaurus.

2020s

Despite attempts to locate more complete Spinosaurus remains, only fragments continued to be found, and it remained a frustratingly poorly-known species even into the early 2010s.

Finally, in 2014, almost a full century after it was first described and named, Spinosaurus started to reveal its secrets with the announcement of the discovery of the most complete skeleton so far, discovered in the Kem Kem fossil beds in Morocco. Its body was still only partially represented, but it included skull fragments, part of a hand, a complete leg and pelvis, some sail spines, and several vertebrae from the neck, back, and tail.

And nobody was expecting what these pieces revealed.

It had a very long torso and proportionally short stumpy legs, and was reconstructed with a huge distinctive “M-shaped” sail on its back. Its feet had flat-bottomed claws and its “dewclaw” toe was enlarged into an extra weight-bearing digit – adaptations for spreading its weight over soft muddy ground, and suggesting its feet may also have been webbed. Initially it was also presented as possibly being quadrupedal, due to how far forward its center of mass seemed to be, reviving an odd idea from the late 20th century.

Along with its long crocodile-like head and conical teeth, this was interpreted as evidence it was a semiaquatic fish-eating swimming animal – potentially making it the first known semiaquatic non-avian dinosaur. Spinosaurids had been suggested to be specialized piscivores before, especially since Baryonyx had been found with fish scales in its stomach, but they were generally assumed to be more like modern grizzly bears, wading into water to hunt but not being habitual swimmers. Spinosaurus’ weird croco-duck proportions, however, seemed like they might be much more suited to watery habitats than to the land.

Since Spinosaurus had become a popular dinosaur with the general public by that point, the discovery was big news – and a big controversy for a while. It was so bizarre that some paleontologists were skeptical of the radical new interpretation, wondering if the measurements of the skeleton were correct or if the short legs were even from the same individual or the same species as the rest of the bones.

After a while the new proportions were accepted as fairly accurate, and over the next few years attention turned to instead figuring out just how this animal worked and how aquatic it actually was. An earlier isotope analysis of its teeth supported a semiaquatic lifestyle similar to crocodiles and turtles, but a buoyancy study argued that it might not have been able to dive below the water suface and its sail made floating unstable – but also found that its center of mass was closer to its hips than previously calculated, suggesting it could walk bipedally after all.

Then in 2020 came another surprise: more of the tail of the new specimen had been found, and it was just as weird as the rest of Spinosaurus. Its tail was a huge vertically flattened paddle-like fin supported by long thin neural spines and chevrons, resembling a giant eel or newt more than a dinosaur and also giving some more weight to the idea that it was a swimmer.

Our modern view of Spinosaurus is still evolving, and likely to be full of even more surprises in the future as we discover more about this unique dinosaur. But we at least know it lived in what is now North Africa during the Late Cretaceous, about 99-93 million years ago, and whether it was a swimmer or wading generalist predator it was one of the largest known theropods to ever live, estimated to have reached around 16m long (~52ft).

While the “M-shaped” sail reconstruction has been popularized by the recent discoveries, the exact shape of this structure is still unknown. Like with other sailbacked animals it’s also not clear what it was for, with ideas including temperature regulation, visual display, supporting a fatty hump, and a potential hydrodynamic adaptation.

EDIT: And while I was working on this entry (late March 2022) I missed that another study had just come out with more anatomical support for swimming Spinosaurus!

Retro vs Modern #22: Tyrannosaurus rex

Probably the most famous and popular dinosaur of all time, Tyrannosaurus rex is also the only species commonly known by both its full scientific name and its abbreviation T. rex.

1900s-1960s

Fragments of what we now know are Tyrannosaurus fossils were first found in the Western United States in the 1870s, but it wasn’t until the early 1900s that a couple of partial skeletons were discovered and recognized as belonging to a new species of huge carnivorous theropod.

With its charismatic and memorable name meaning “tyrant lizard king” it was an immediate hit with the general public, portrayed as the “king of the dinosaurs” in pop culture and as the dramatic nemesis of Triceratops.

Like other bipedal dinosaurs of the time it was depicted in an upright kangaroo-like tripod pose, cold-blooded and lizard-like. Sometimes it was also shown with three-fingered hands, since its arms were poorly known for a long time – and while the closely-related tyrannosaurid Gorgosaurus was known to have had just two fingers, this wasn’t confirmed for Tyrannosaurus until the late 1980s.

1990s

During the 1970s and the early Dinosaur Renaissance it became obvious that bipedal dinosaurs like Tyrannosaurus couldn’t have stood so sharply upright without dislocating their hips and tail vertebrae.

Jurassic Park was influential in introducing this new corrected posture to the general public in the early 1990s, presenting a powerful and active predator with a more bird-like horizontal stance and its tail acting as a counterbalance. Reconstructions inspired by this portrayal became standard for Tyrannosaurus during the 1990s (although the old-style tripod remains in public consciousness even decades later), and while it didn’t tend to get as heavily shrinkwrapped as some other species it was still common for a while to push its belly ribs in as much as possible to make its bulky body look skinnier and more “athletic”.

The 1980s and 1990s were also a time when discoveries of new Tyrannosaurus specimens began to become much more frequent, improving knowledge of the species’ anatomy, biology, and life history. Some, like Sue, Stan, and the Dueling Dinosaurs, would also unfortunately end up becoming highly controversial, tied up in legal disputes for years and sold for multi-million-dollar prices.

2020s

After the explosion of feathered non-avian dinosaur specimens from China in the mid-1990s, eventually the small feathered tyrannosauroid Dilong was discovered in the early 2000s, followed by the much larger-bodied Yutyrannus in the early 2010s.

While these tyrannosauroids weren’t particularly closely related to Tyrannosaurus itself, the question of potential tyrant fuzz still began to loom, and for a while in the 2010s highly fluffy T. rex interpretations were popular in paleoart. But in the late 2010s a study of known skin impressions from Tyrannosaurus and several of its closer relatives showed that small pebbly scales were known from various parts of the body, and suggested that these particular dinosaurs were most likely primarily scaly. Sparser fluff was still possible on parts of the body, however, similar to the hair on modern elephants, and it’s also possible that juveniles were much fuzzier.

(While this is disappointing for fans of huge fatbird T. rex, it’s also a great example of the scientific process. The skin impressions hadn’t ever been properly described before this point, and the scaly interpretation had mostly been an assumption. Speculative fluffiness prompted all the skin evidence to actually be consolidated, and now we know a lot more about Tyrannosaurus’ potential outward appearance than we did before.)

Arguments about lips in theropod dinosaurs also went back and forth during the 2010s, with interpretations ranging from tight-skinned crocodilian-like snouts with exposed teeth to fleshy lizard-like lips similar to modern Komodo dragons. There’s not really a consensus yet, but since most non-beaked tetrapods do have lips the safe bet is still that dinosaurs like Tyrannosaurus would have had them too. 

Our modern view of Tyrannosaurus is a much chunkier animal than older interpretations, with  more extensive soft tissue, properly-positioned belly ribs showing that it had a barrel-shaped pot-bellied body, and its tail being thicker-muscled than previously thought.

Living across western North America – then the island continent of Laramidia – during the very end of the Cretaceous, about 68-66 million years ago, it was one of the largest terrestrial carnivores to ever live. The very biggest known specimens are estimated to have been as much as 13m long (~43′), with the proportionally large head making up around 1.5m of that (~5′).

Its skull was boxy at the back but narrow along the snout, allowing its forward-facing eyes to have hawk-like stereoscopic vision. Large fenestrae and a “honeycomb” of air spaces reduced the weight of the skull, while reinforced fused bones strengthened it, and Tyrannosaurus is estimated to have had an incredibly powerful bone-crushing bite force.

It had a highly developed sense of smell, and its hearing was geared towards low-frequency sounds. The texture of its skull bones suggests it may also have had thick toughened keratinous skin and bumps over its face, which might have been involved in head-shoving and headbutting behaviors.

Although proportionally tiny for its overall size, its arms were still rather beefy, with large areas for muscle attachment with “meathook” claws that may have been used to hold onto struggling prey.

As a heavily-built bulky carnivore it probably wasn’t especially fast, and its legs were adapted for energy-efficient walking rather than running. It may have been a long-distance stalker, only using short bursts of speed in a final ambush – and like most large carnivores it would have also opportunistically scavenged on carcasses, too.

Specimens once argued to belong to a separate smaller species of tyrannosaur, “Nanotyrannus“, are now generally accepted as actually being juvenile Tyrannosaurus. They show a surprising amount of physical change as these animals aged, starting out leaner-built with longer legs more suited for speed, slender more delicate snouts, and only developing the characteristic chunky adult proportions during a huge growth spurt in their mid-to-late teens.

Meanwhile, the latest big controversy over this dinosaur as of March 2022 (because there’s always something) is a study proposing splitting Tyrannosaurus into three separate species: T. rex, T. imperator, and T. regina. It doesn’t seem to be going down well, but much like the feather situation it probably at least means we’re going to see a lot of further investigation over the next few years.

Retro vs Modern #21: Deinonychus antirrhopus

Deinonychus antirrhopus was one of the most significant dinosaur discoveries of the 20th century, kicking off the Dinosaur Renaissance and the recognition of the evolutionary link between maniraptoran theropods and modern birds.

1960s

The first remains of this species were discovered in North America in the 1930s, but at the time the fossils weren’t officially described or named. It wasn’t until the 1960s that more specimens were found in Montana, representing at least three preserved individuals, and paleontologist John Ostrom recognized that there was something very special about this dinosaur.

In contrast to the prevailing view at the time that theropods were all upright tail-dragging “sluggish lizards” this was clearly a highly specialized and active predator, with a huge sickle-shaped claw on each foot and a long stiff tail for balance – inspiring its scientific name’s meaning of “counterbalancing terrible claw”.

And while the very first reconstruction of Deinonychus might seem retro to modern eyes, at the time it was revolutionary and it went on to become an iconic representation of the species for the next couple of decades. Drawn by Robert Bakker, who was Ostrom’s student at the time, it depicted a lizard-like creature with its body held in a horizontal pose and its tail held out straight behind it. Its head was portrayed as more domed than we now know Deinonychus’ skull to have been, and its neck was up in an alert posture while the animal ran at full sprint, with its sickle-claws held up away from the ground to keep them sharp.

A few years later further discoveries showed a highly bird-like pelvis and hands very similar to those of Archaeopteryx, triggering the Dinosaur Renaissance reinterpretation of dinosaurs as active warm-blooded animals, and the revival of the 19th century idea that they were the ancestors of birds.

1980s-1990s

As the “birds are dinosaurs” idea began to gain acceptance with increasing amounts of anatomical evidence, some paleontologists in the 1980s began to also suspect that highly bird-like dromaeosaurids like Deinonychus might have also been feathered. Some reconstructions during this time showed this to varying degrees, particularly those drawn by Bakker and by Gregory Paul – but it didn’t really catch on more widely at first, for one very big reason:

Jurassic Park happened.

Dromaeosaurs hadn’t been well-known dinosaurs to the general public before that point, but the 1993 JP “raptors” were an instant hit in pop culture. Physically based much more on Deinonychus than on Velociraptor, and exemplifying the renaissance view of dinosaurs in major media for the first time, the movie’s fully scaled and oversized version of these animals dominated popular depictions for years afterwards. Even the most rigorous and anatomically accurate artwork showcasing their bird-like features still usually kept them completely naked to retain that familiar reptilian appearance.

Most 1990s attempts at any feathering tended towards being as sparse as possible – often along with the shrinkwrapping typical for the era – at best being decent for the time but what we’d now deride as “half-assed”, and at worst being “a few token quills on the back of the head”.

Deinonychus fossils found in association with Tenontosaurus were also interpreted as being evidence of cooperative pack hunting behavior during this time, and it became a common paleoart meme to depict the large herbivore being constantly swarmed by ravenous raptors.

2020s

The mid-1990s discovery of fully-feathered dinosaurs like Sinosauropteryx in China, followed a few years later by raptors with wing-feathered arms like Sinornithosaurus, gradually began to put the fluff back onto dinosaurs like Deinonychus.

(…At least in reasonably scientific paleoart. The much much stronger and ongoing resistance from popular culture is far too big a subject to get into here. But maybe, just maybe, we’re finally hitting a turning point there?)

Early attempts at properly feathering dinosaurs were a bit awkward, usually looking rather like a bunch of scruffy greasy hair glued onto a scaly raptor, a dinosaur wearing fuzzy pajamas, or like the old “bird-lizard” depictions of Archaeopteryx. Even into the early 2010s some paleoart memes were still common in depictions of dromaeosaurs, but increasingly better understanding of their anatomy and plumage arrangements over the last decade or so has brought us to a much more birdlike interpretation of these animals – with paleoartists like Emily Willoughby being especially influential in popularizing the modern view of dinosaurs like Deinonychus.

We now know Deinonychus lived during the Early Cretaceous, about 115-108 million years ago, in what is now the Mountain West and South Central United States. Up to around 3.4m long (11′), it stood about 1m tall (3’3″), similar in size to a large dog.

It had blade-like teeth in its jaws, and forward-facing eyes with stereoscopic vision. Its three-fingered arms would have been covered by wing-like feathers, and its tail probably had feathers all the way along its length and was stiffened but not totally inflexible.

It may have used the sickle-claws on its feet to pin down struggling prey, eating it alive while flapping its wings and waving its tail for balance. And while often depicted as an extremely fast-runner, its leg proportions and foot anatomy suggest it was actually built more for walking and had an especially strong grip strength in its feet, trading speed for power and probably being more of an ambush predator – often being compared to a “giant ground-hawk”.

Pack hunting has been called into question recently, too, arguing that the Tenontosaurus sites may actually represent crocodile-like or Komodo dragon-like behavior with mobs of scavenging individuals congregating at a carcass. But other evidence from trackways and Utahraptor does offer potential support for pack behavior in raptors, so it’s still open to interpretation.

Retro vs Modern #20: Deinocheirus mirificus

Discovered in Mongolia in the mid-1960s, and named in 1970, Deinocheirus mirificus was a famous paleontological mystery for over 40 years.

1970-2000s

For a long time all that was known of this dinosaur was a few fragments and an enormous pair of arms – some of the largest of any known theropod at 2.4m long (7’10”) – inspiring its name meaning “wonderful terrible hands”.

Initially it was classified as a new type of carnosaur (which was something of a wastebasket group at the time), but similarities with the “ostrich-mimic” ornithomimosaurs were soon noted in the early 1970s. And despite some paleontologists trying to link Deinocheirus to the similarly big-armed therizinosaurs over the decades, the ornithomimosaur interpretation seemed to have won out by the early 2000s.

Depictions of Deinocheirus during this time period were highly speculative and reflected the uncertainty over its evolutionary relationships, varying from giant carnosaurs to therizinosaur-like forms to “Gallimimus but bigger” – or sometimes simply showing a hilarious pair of monster-arms reaching in from out-of-frame. Many popular dinosaur books just gave up entirely and only illustrated the known fossil material unreconstructed, and an iconic photograph of Mongolian paleontologist Altangerel Perle standing between the arms was commonly used to emphasize the sheer scale of the bones.

2020s

In the early 2000s attempts to find more fossil material at the original discovery site had only turned up a few additional fragments, including some belly ribs with evidence of having been bitten by a Tarbosaurus – suggesting that the specimen represented the scattered dismembered bits left behind by a feeding carnivore, and that the rest of the carcass might not even have fossilized.

But then between 2006 and 2009 a team of international paleontologists working in Mongolia found a couple of unusual partial skeletons at sites that had been looted by fossil poachers. While parts like the skulls and feet had been taken, the two specimens were still fairly complete and one still had enough arm material left to clearly identify it as Deinocheirus.

When the discovery was announced at the 2013 Society of Vertebrate Paleontology conference it was massive surprise to most of the paleontological community, confirming that Deinocheirus was indeed an ornithomimosaur, and that it was an incredibly weird one. Heavily-built, it was a much chunkier animal than its other relatives, and most surprising of all it had a humped “sailback” formed by long neural spines on its back vertebrae.

Then things got even better.

And stranger.

A “weird skull” had been spotted in the private fossil trade in Europe in 2011, along with some hand and foot material that perfectly matched the missing pieces of one of the new Deinocheirus specimens. The fossils were acquired and donated to a Belgian museum, and then finally were repatriated to Mongolia in 2014, filling in the rest of Deinocheirus’ appearance with a suitably surprising head to go with the rest of its body.

We now know Deinocheirus lived about 70 million years ago during the Late Cretaceous, in what is now the Gobi Desert but at the time was a river-delta-like environment with numerous river channels, shallow lakes, and mudflats.

It grew up to about 11-12m long (~36-39′) and had a long narrow skull with a wide beak and a deep lower jaw – resembling a hadrosaur more than an ornithomimosaur – and it had a rather small brain for a theropod of its size, proportionally closer to that of a sauropod. Its fairly weak jaw muscles suggest it mainly fed on soft vegetation, possibly foraging for aquatic plants in bodies of water like an enormous duck. Gastroliths in its gut helped to grind up its food, and the remains of fish in its stomach suggest that it was also somewhat omnivorous.

Its characteristic huge arms were actually one of the least strange things about it, and were actually proportionally smaller compared to its body size than other ornithomimosaurs. They were heavily muscled, though, with large curved claws, and may have been used to dig up food from mud and soft soil or to pull clumps of vegetation closer.

Its skeleton was highly pneumatized, full of lightening air sacs, but it was still a very big and bulky animal with relatively short legs that suggest it was rather slow-moving. Its feet resembled those of both hadrosaurs and tyrannosaurs, with blunt claws and adaptations for heavy weight-bearing in a bipedal stance.

The large sailback may have been a display structure, and the tip of its tail resembled a pygostyle and so may have sported a fan of feathers. The rest of its body was probably feathered similar to what’s known from other ornithomimosaurs, although potentially more sparsely due to its huge size.

Retro vs Modern #14: Therizinosaurus cheloniformis

Therizinosaurs were some of of the most unique theropod dinosaurs. It’s only in the last few decades that we’ve started to understand much about them, and they’re still somewhat enigmatic even today.

1950s

The first known therizinosaur fossil discovery was Therizinosaurus cheloniformis, found in Southern Mongolia during the late 1940s and described and named in the mid-1950s based on a few fragments that included some unusually large and elongated claws.

These remains were interpreted as belonging to a giant turtle-like reptile that used its scythe-like claws to harvest aquatic plants – inspiring both parts of its scientific name, with Therizinosaurus meaning “reaper lizard” and cheloniformis meaning “turtle-shaped”.

1990s

The turtle interpretation began to be questioned during the 1970s, and the discovery of some slightly better (but still fragmentary) specimens reclassified Therizinosaurus as an unusual theropod dinosaur.

In the late 1970s and early 1980s fossils of another group of dinosaurs known as “segnosaurs” were also starting to be discovered, with a confusing mixture of anatomical features that seemed to link them to multiple different dinosaur lineages. As a result opinions about their evolutionary relationships varied during the 1980s, sometimes considering them to be theropods, sometimes late-surviving “relic” prosauropods, and sometimes a whole new major lineage of rare and weird saurischians.

Similarities between segnosaurs and the known material of Therizinosaurus were soon noted, and the discovery of the fairly complete Alxasaurus in the early 1990s confirmed that they were all part of the same group of bizarre herbivorous theropods – and the name “segnosaurs” was dropped in favor of “therizinosaurs”, since older names usually get priority in taxonomy.

Reconstructions of Therizinosaurus during this time tended to look rather weird and awkward. As with the majority of dinosaurs during this period it was depicted as entirely scaly and reptilian, and was often shown with a stiff hunched downcurving neck and an oddly tiny-looking tail.

Further discoveries during the 1990s finally began to clarify therizinosaurs’ evolutionary affinities, eventually placing them as an early branch of bird-like maniraptoran theropods, closely related to both oviraptorosaurs and the alvarezsaurs – and in 1999 the discovery of the small early therizinosaur Beipiaosaurus helped to confirm this relationship, revealing impressions of an extensive coat of filamentous feathers and longer stiffer quill-like structures.

2020s

Over the next couple of decades more and more therizinosaur fossils were found in both Asia and North America, and details about these dinosaurs’ appearance, biology, and ecology gradually became better understood. While there’s still a lot we don’t know about them, we do now at least have some fairly complete examples like Nothronychus, fossilized therizinosaur footprints, more feathers, an idea of Beipiaosaurus’ coloration (it was brown!), and even eggs and potential colonial nesting sites.

And while Therizinosaurus itself is still only represented by fragmentary and incomplete material, we now have a much better idea of what it was probably like. It lived in what is now the Gobi Desert during the Late Cretaceous, about 70 million years ago, and would have been both the largest known therizinosaur and the largest known maniraptoran dinosaur, estimated to have been as much as 10m long (33′) based on the proportions of its relatives.

It would have had a tiny head with a toothless beak at the front of its jaws, a long neck, and a wide bulky “pot-bellied” body housing its huge plant-fermenting gut. With its especially large body size it probably wasn’t as extensively feathered as its smaller relatives, but it may have still been sparsely fuzzy across parts of its body.

Unlike most other theropods it walked on all four toes of its feet, with the dewclaw enlarged into an extra weight-bearing digit. Recent analysis of footprints has also suggested that the larger therizinosaurs like Therizinosaurus may actually have been plantigrade, walking with their feet completely flat on the ground. This might turn out to just be an artifact of how the tracks were preserved, but therizinosaurs are certainly already weird enough that it could be a plausible interpretation.

But Therizinosaurus’ most distinctive feature was its hands, with extremely long narrow claws each at least 50cm long (1’8″). Unlike the strongly curved claws seen in other therizinosaurs, these ones were fairly straight for most of their length, only curving more sharply towards their tips.

While in the past these claws have been proposed as being weapons or digging adaptations, they were actually relatively delicate and were probably mainly used for pulling clumps of vegetation closer in a convergently similar manner to the later mammalian chalicotheres and ground sloths.

Therizinosaurus would have been a heavy slow-moving animal, and probably spent a lot of time sitting on its haunches supported by its especially robust hip bones while it browsed on large amounts of vegetation. It likely relied on its pure bulk and intimidation to deter potential predators, possibly even making aggressive displays with its claws when threatened – essentially it may have been a giant goose-sloth.

Retro vs Modern #13: Stegosaurus stenops

The first known stegosaur fossils were found in England and South Africa between the 1840s and 1870s, but these dinosaurs weren’t properly recognized as a highly distinctive group until the discovery of Stegosaurus itself in North America during the late 1870s.

1880s

The first Stegosaurus reconstructions were based on fragmentary and disarticulated fossil material, and its life appearance was very poorly understood. Initially it was depicted as a bipedal long-necked animal, with its plates laying flat against its back like a turtle shell, numerous spikes across its back, and more plates running along its tail.

1890s-1970s

Better skeletons of the species Stegosaurus stenops were discovered in the late 1880s, and by the 1890s stegosaur anatomy was becoming clearer. Reconstructions quickly adopted an arch-backed body shape with a tiny head and drooping tail, short semi-sprawling forelimbs and long hindlimbs, and with the plates now properly upright on the back and the spikes at the end of the tail.

Stegosaurus‘ unique appearance rapidly made it one of the most famous and recognizable dinosaurs to the general public. Its comical-seeming tiny head and even tinier brain also unfortunately ended up contributing to the prevailing early 20th century attitude that dinosaurs were sluggish and unintelligent, with the myth that it needed a “second brain” in its hips to control its huge body becoming a popular notion for quite some time.

The exact arrangement of the iconic back plates and tail spikes was uncertain for several decades, with early versions in the 1890s having up to eight tail spikes and a single row of plates. This was then updated in the 1900s to a double row of symmetrical plate pairs, and by the 1920s the standard arrangment had soon become an alternating two-row pattern with the tail spikes reduced to four – a layout that’s still considered correct today.

2020s

In the second half of the 20th century a combination of numerous new stegosaur species from China and the Dinosaur Renaissance began to revise the way Stegosaurus was understood, bringing it into a fully upright posture with its head and tail held high, and recognizing the convergently sauropod-like anatomy of its hands and feet.

But something still wasn’t right.

Compared to other known stegosaurs, Stegosaurus itself was starting to seem… rather weird. Its short neck, short forelegs, giant plates, sloping back and high rump were much more exaggeratedly proportioned than any of its relatives.

This was finally resolved in the 2010s when a near-complete specimen nicknamed “Sophie” was thoroughly described – and revealed that Stegosaurus’ proportions had been wrong the whole time. All previous skeletal reconstructions had been composites, put together from remains of multiple individuals that had all been different ages and sizes, and in the process had heavily distorted our idea of what this animal actually looked like.

Our modern view of Stegosaurus is now a much more typical stegosaur than before. It lived during the Late Jurassic, about 155-145 million years ago, across the Western and South Central United States (with a possible additional occurence in Portugal), alongside several other iconic dinosaurs of the “Jurassic savanna” like Brontosaurus, Diplodocus, and Allosaurus.

It grew up to around 9m long (~30ft), and had a small head with a long narrow snout, with a toothless beak at the front of its jaws and small peg-shaped teeth further back. Bony ossicles lined the underside of its neck, possibly providing chainmail-like protection to its throat, and its skin was covered in tiny pebbly scales interspersed with “rosettes” formed around slightly larger oval scales. Its neck was longer than previously thought, more in line with other stegosaurs, and its torso and hind legs were a bit shorter, making its posture more horizontal and its back less arched.

The actual function of the large back plates is still uncertain. Ideas about them being defensive armor (and speculation about them even being moveable!) have mostly been discounted at this point, since they were actually relatively fragile – although their keratinous covering may have had a fairly sharp edge. Thermoregulation has been a popular explanation for many decades, with blood vessel impressions in the plates being proposed as evidence they were used as “radiators” to prevent overheating like the ears of modern African elephants.

But currently the most likely primary plate function is thought to be visual display, with the large plates increasing the perceived size of Stegosaurus either to intimidate predators and rivals or to impress potential mates. If this was the case then they may have also been strikingly colored and patterned in life.

Meanwhile the “thagomizer” on its tail actually does seem to have been a weapon, with injuries to that area of the body being fairly common, and several Allosaurus fossils have been found with puncture wounds the exact size and shape of Stegosaurus spikes. Articulated specimens have also shown that the tail curved downwards at the tip, holding the thagomizer with the spikes pointing horizontally outwards and backwards.

Retro vs Modern #12: Edmontosaurus annectens

Hadrosaurs were first discovered during the 1850s in North America, with the eponymous Hadrosaurus being both one of the most complete dinosaurs known at the time and also the first dinosaur skeleton to ever be mounted and displayed.

Like many other dinosaurs of the time hadrosaurs were initially reconstructed as bipedal with an upright kangaroo-like pose. Early in the history of their study their wide flat “duckbill” snouts were thought to indicate they were semi-aquatic, and they were frequently portrayed swimming and wading while feeding on soft water plants.

While elaborately bony-crested hadrosaurs like Parasaurolophus have become some of the most famous and recognizable members of the group, the species that’s gone through the most radical changes in our understanding in recent years is probably Edmontosaurus annectens.

1890s-1960s

Edmontosaurus has had an especially messy taxonomic history with various specimens spending decades under many different names, commonly being labelled as Anatosaurus and Trachodon for much of the 20th century. For the sake of avoiding a lot of confusion I’m just going to keep referring to it here as “Edmontosaurus”, even though the naming issues weren’t properly sorted out until the 1990s.

The earliest specimen of what we know call Edmontosaurus was discovered in the 1890s, and the first to actually bear the genus name was the closely related species Edmontosaurus regalis discovered in the 1910s. For many decades it was mostly reconstructed in the then-typical “tripod” posture and seen as being highly aquatic, with an exceptionally well-preserved “dinosaur mummy” specimen being used to support that view – skin impressions around its hands were interpreted as paddle-like webbing used to swim.

The mummy also showed fairly thin and delicate skin, with a pattern of many tiny scales dotted with clusters of larger scales, and what appeared to be a fleshy skin frill running along Edmontosaurus’ neck and back.

2020s

The idea of amphibious hadrosaurs was finally challenged in the mid-1960s, at the start of the Dinosaur Renaissance, with details of their anatomy, possible stomach contents, and the environments that their fossils had been preserved in all being used to help reinterpret them as fully terrestrial herbivores that walked on four legs and ran on two. The discovery of Maiasaura nesting colonies in the late 1970s also revealed a lot of new information about the life history of these dinosaurs, and helped to popularize the image of them as social animals living in herds and caring for their young.

From the 1990s onwards new discoveries of additional “mummies” of both Edmontosaurus and other hadrosaurs have given us even more insights into the soft parts of their anatomy. Their necks and tails were much more thickly muscled and chunky than their skeletons alone suggest, the frill may have had a sort of rectangular segmented appearance, and the webbing on their forelimbs was actually more of a “mitten” that bound their hands into fleshy weight-bearing pads. And instead of a broad “duckbill” they actually had large hooked beaks covering their snouts, giving then more of a horse-like head shape.

We now know Edmontosaurus lived during the very end of the Cretaceous, about 73-66 million years ago, with the older part of that time range represented by Edmontosaurus regalis in Western Canada and the younger part represented by Edmontosaurus annectens in Western Canada and the Western and West North Central United States. It was one of the largest known hadrosaurs with most adult specimens around 9-12m long (~30-39′), but some of the very largest known partial remains suggest the existence of rare enormous “super-adults” that were about 15m long (49′).

Edmontosaurus was probably a grazing animal primarily eating tough low-growing foliage like horsetails, cropping off mouthfuls with its beak and then grinding them up with batteries of hundreds of teeth in the back of its jaws using a unique complex chewing motion.

Its skin had a complex texture of varying scale shapes and sizes across its body, and one mummified specimen of Edmontosaurus regalis shows a raised bumpy pattern of large scale clusters on its neck and a fleshy crest on the top of its head. It’s currently unclear if these were sexually dimorphic features and we don’t know if Edmontosaurus annectens actually had them too, but I’ve speculatively included them in this reconstruction anyway.

And despite being one of the most intensely-studied and completely known non-avian dinosaurs in the world, Edmontosaurus is somehow still continuing to surprise us. Parts of the mummy specimen nicknamed “Dakota” are still being carefully prepared, and in late 2019 the North Dakota Geological Survey teased an unexpected discovery – a large single hoof-like nail on the front of its hand, unlike anything ever seen before on a dinosaur, and suggesting that Edmontosaurus may have been much more specialized for purely quadrupedal movement than previously thought.

Official details on the “hoof” still haven’t been published yet, but whenever it happens it’ll be exciting to find out just what’s actually going on there.

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.