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 #19: Quetzalcoatlus northropi

Named after an Aztec deity and often called “the largest animal to ever fly”, Quetzalcoatlus northropi is probably the most famous large pterosaur after Pteranodon – but despite its popularity for a long time we actually knew very little about it.


1970s

Discovered in Texas in the United States during the early 1970s, the first known fossils of Quetzalcoatlus were just a few giant wing bones, along with several partial skeletons of smaller individuals which at the time were thought to be juveniles.

But although it was given its charismatic name in 1975, the fragmentary nature of the find and it only being given a brief non-formal description meant it was very poorly understood at the time. Worse, the known fossil material was notoriously difficult for other paleontologists to study for several decades afterwards, with the museum housing it often refusing access requests entirely or demanding promises of total secrecy from anyone who was actually allowed to see it.

Most pterosaurs at the time were thought to be soaring seabird-like fish-eaters, but this huge species had been discovered in an inland environment. So Quetzalcoatlus was interpreted as being a huge vulture-like scavenger, with early reconstructions based on this idea ending up highly speculative due to the lack of good anatomical information. A common paleoart meme in the 1970s and 1980s depicted it with a long snake-like neck, a bizarrely tiny head, snaggly teeth, and a small nub-like crest.


1990s

In the mid-1980s Quetzalcoatlus was recognized as belonging to the newly-discovered azhdarchid lineage, a group with extremely long necks, toothless beaks, and long legs – although these pterosaurs were also rather poorly-known until more complete specimens were found in the mid-to-late 1990s.

Reconstructions during this period were considerably less demonic, reflecting the changing ideas about pterosaurs at the time. Quetzalcoatlus became sleeker and more bird-like, depicted with long narrow wing membranes, its neck held in an S-curve, its legs sticking out straight behind it in flight, and sometimes pycnofiber fuzz on parts of its body.

(…And sometimes there was excessive shrinkwrapping.)

During the early 1990s Quetzalcoatlus was also often shown with a blunt chunky beak based on fossil jaws found in west Texas, but in 1996 these remains were determined to belong to a different pterosaur. At the same time more material of the “juveniles” suggested they actually represented an entire second species of Quetzalcoatlus, about half the size of Quetzalcoatlus northropi, with partial skulls showing evidence of a bony crest on the head.

Quetzalcoatlus was also interpreted as a skim-feeder during this time, thought to fly along just above bodies of water with its lower jaw trawling over the surface, snapping up any fish it contacted.


2020s

The skimming hypothesis was widely accepted until 2007, when a detailed study showed that it was physically impossible for any pterosaurs to have actually fed that way. Based on their anatomy and known habitats azhdarchids like Quetzalcoatlus were subsequently reinterpreted as highly terrestrial predators, spending a lot of their time stalking around on all fours snagging prey in their huge beaks like a stork with the proportions of a giraffe.

A full technical description of the known fossil material had been promised since the early 1980s, but decades had passed and by the 2010s it still hadn’t been published. The specimens continued to be inaccessible, information was still under heavy embargo, and what little had been published in the 1970s and 1990s was argued to be sparse enough and undiagnostic enough that it was starting to be genuinely unclear if Quetzalcoatlus northropi was even a valid species name at all.

Finally, finally, after over 40 years, a whole collection of papers about this pterosaur were released in 2021 – and in a refreshing contrast to the many years of secrecy and hoarding they were all free and open access. The second species finally got a name, Quetzalcoatlus lawsoni, and the genus as a whole is now properly and officially defined, instantly going from dubious and almost unknown to one of the most complete azhdarchids so far.

The study isn’t without its issues or controversy, particularly in regards to some of its retro-seeming interpretations of Quetzalcoatlus’ posture, proportions, and launch mechanics. But since the publication means that the fossils are finally unrestricted to other researchers, there’s probably going to be plenty more studies and arguments and new discoveries about it in the future.

While Quetzalcoatlus northropi is still only known from fragments, the new knowledge about its smaller relative means we now have a much better idea of what it was probably like. It lived at the very end of the Cretaceous period, about 68-66 million years ago, and is currently known just from Texas – but it probably ranged much further than that, since azhdarchids are thought to have been able to fly for potentially thousands of kilometers at a time using energy-efficient thermal soaring.

It was one of the largest animals known to have been capable of powered flight, but not necessarily the largest ever. Some past Quetzalcoatlus wingspan estimates got ridiculously over-enthusiastically huge, in some cases up to to 21m (69′), but modern estimates based on better knowledge of azhdarchid proportions suggest something shorter-winged and much closer to 10m (33′) – and some other azhdarchids are now thought to have had similar or possibly even slightly larger wingspans.

Still, Quetzalcoatlus was very big, and when standing on all fours it was probably similar in size and shape to a modern giraffe, about 6m tall (~20′) with at least half of its height just being its neck. It had limb proportions more like an ungulate mammal than most other pterosaurs, suggesting it was highly adapted for walking and running around on the ground – but it could also catapult itself up into the air using its powerful forelimbs to take flight.

It would have been a ground-stalking predator similar to some modern storks and ground hornbills, using its long sharply pointed beak to snatch up any smaller animals it could fit into its mouth. Since its Texan habitat was a semi-arid “fern prairie” dominated by the titanosaur Alamosaurus, hatchlings and small juveniles of this sauropod may have made up a major part of Quetzalcoatlus’ diet. 

Retro vs Modern #18: Pterodactylus antiquus

Pterodactylus antiquus was the first pterosaur ever discovered, and in popular culture the name “pterodactyl” has become commonly associated with the group as a whole.


1800s

The first known Pterodactlyus specimen came from southeast Germany, and was described (although not yet named) in the 1780s. The modern concept of extinction hadn’t yet been established, so at the time unknown fossil species were generally assumed to still exist alive somewhere in remote regions of the world. Initially it was unclear what type of animal this specimen represented, and it was interpreted as being aquatic because the oceans seemed like the best place for such a strange creature to hide undiscovered.

In 1800 it was recognized as instead being a flying animal, with naturalist Johann Hermann creating both the first known life restoration of a pterosaur and one of the first known examples of scientific paleoart in general. He depicted it as a bat-like mammal with extensive wing membranes, external ears, and a covering of fur, and made two different sketches of this interpretation. The first shows an odd rounded wing shape with the wing finger seeming to form a stiff “hoop” around to the ankles, but the second version has some interesting additions – showing an understanding of the wing finger being straightened and stretching out the membrane, and adding a very large colugo-like propatagium between the neck and the wrist.

In light of our modern understanding of pterosaurs this was an incredibly good attempt at a reconstruction, despite the total lack of soft tissue impressions and the mistaken mammal classification.

The name Pterodactylus was established for this animal by the late 1810s, and while it was correctly identified as a flying reptile by some early paleontologists, others also saw it as being more mammal-like or bird-like.

In this pre-Darwinian time there was no modern concept of evolutionary relationships, and pterosaurs were instead thought to be a type of bat positioned inbetween mammals and birds in the “chain of being“. This “bat model” became influential on the early study of pterosaurs, and some paleontologists depicted highly mammalian versions even as late as the 1940s.

(The aquatic interpretation also stuck around as a competing idea until at least 1930, with  Pterodactylus‘ wings restored as huge penguin-like flippers.)


1850s-1970s

By the mid-19th century the reptile interpretation had become standard but the bat influence remained, with pterosaurs commonly assumed to have been furry, warm-blooded, and quadrupedal and clumsy on the ground. Fossil evidence of hair-like fuzz had even been found on a specimen of Scaphognathus in the 1830s, but this was later disputed and was only confirmed as being real almost two centuries later.

British paleontologist Richard Owen disagreed with the bat model for pterosaurs, considering them to be scaly sluggish cold-blooded gliders, and in the 1850s oversaw the creation of the heavily-scaled and oddly goose-like Crystal Palace Pterodactylus statues – one of their first major portrayals to the general public, and influential in the popular perception of these animals at the time.

But even into the start of the 20th century some paleontologists were still arguing for active warm-blooded pterosaurs, with the first popular book on the group in 1901 suggesting they were closely related to birds. German paleontologists continued to interpret pterosaurs this way into the 1930s, but in contrast English and American scientists largely lost interest in these animals over subsequent decades – and depictions of pterosaurs went the same way as non-avian dinosaurs during this period, descending into awkward evolutionary failures that could barely even fly, shown as scaly-skinned or naked, and hanging upside-down from trees and cliffsides like giant wrinkly bats.


2020s

The discovery of definite hair-like structures (known as pycnofibers) on Sordes brought pterosaurs into their own renaissance in the 1970s, and among a flood of new discoveries they were reinterpreted as active warm-blooded bird-like animals. Reconstructions sometimes went a bit too bird-like, though, attempting to distance themselves from the older saggy-repto-bat portrayals, with forced bipedal postures and much more slender wing membranes attaching to the waist.

But early 21st century studies into biomechanics, soft-tissue remains, and trackways confirmed that some elements of the bat model had actually been right the whole time. Pterosaurs had flight membranes attached to their hind limbs and were quadrupedal when on the ground – but instead of being awkward bat-like sprawlers they were actually competent walkers and runners with an energy-efficient upright posture.

We now know Pterodactylus lived during the Late Jurassic, about 150-148 million, at a time when the region of southern Germany was part of an island archipelago in a shallow tropical sea. Fragmentary remains are also known from elsewhere in Europe and in Africa, suggesting this genus had a fairly wide range.

It was a fairly small pterosaur, with the largest adults having am estimated wingspan of around 1m (3’3″), and had long straight jaws lined with numerous pointed teeth. Most known specimens are juveniles, but fossils of larger adults preserve evidence of a soft tissue crest with a backwards-pointing “lappet”, and long mane-like pycnofibers on the back of the neck.

Like other pterosaurs it was fuzzy and warm-blooded, and it had hollow bird-like bones and air sacs lightening its body. Its wings were highly complex with layers of strengthening fibers and muscles that allowed the flight surface shape to be precisely controlled, and when walking on the ground it could fold up its wing fingers and stow the membranes well out of the way of its limbs.

It was probably a generalist carnivore, feeding mostly on small prey like invertebrates, and the shape of the sclerotic rings in its eye sockets suggest it was mainly active during the daytime.

Retro vs Modern #17: Ammonites

Ammonites (or ammonoids) are highly distinctive and instantly recognizable fossils that have been found all around the world for thousands of years, and have been associated with a wide range of folkloric and mythologic interpretations – including snakestones, buffalo stones, shaligrams, and the horns of Ammon, with the latter eventually inspiring the scientific name for this group of ancient molluscs.

(Unlike the other entries in this series the reconstructions shown here are somewhat generalized ammonites. They’re not intended to depict a specific species, but the shell shape is mostly based on Asteroceras obtusum.)


1830s

It was only in the 1700s that ammonites began to be recognized as the remains of cephalopod shells, but the lack of soft part impressions made the rest of their anatomy a mystery. The very first known life reconstruction was part of the Duria Antiquior scene painted in 1830, but to modern eyes it probably isn’t immediately obvious as even being an ammonite, depicted as a strange little boat-like thing to the right of the battling ichthyosaur and plesiosaur.

The argonaut octopus, or “paper nautilus”, was considered to be the closest living model for ammonites at the time due to superficial similarities in its “shell” shape, but these modern animals were also rather poorly understood. They were commonly inaccurately illustrated as floating around on the ocean surface using the expanded surfaces on two of their tentacles as “sails” – and so ammonites were initially reconstructed in the same way.


1860s

While increasing scientific knowledge of the chambered nautilus led to it being proposed as a better model for ammonites in the mid-1830s, the argonaut-style depictions continued for several decades.

Interestingly the earliest known non-argonaut reconstruction of an ammonite, in the first edition of La Terre Avant Le Déluge in 1863, actually showed a very squid-like animal inside an ammonite shell, with eight arms and two longer tentacles. But this was quickly “corrected” in later editions to a much more nautilus-like version with numerous cirri-like tentacles and a large hood.

The nautilus model for ammonites eventually became the standard by the end of the 19th century, although they continued to be reconstructed as surface-floaters. Bottom-dwelling ammonite interpretations were also popular for a while in the early 20th century, being shown as creeping animals with nautilus-like anatomy and numerous octopus-like tentacles, before open water active swimmers eventually became the standard representation.


2020s

During the 20th century opinions on the closest living relatives of ammonites began to shift away from nautiluses and towards the coleoids (squid, cuttlefish, and octopuses). The consensus by the 1990s was that both ammonites and coleoids had a common ancestry within the bactridids, and ammonites were considered to have likely had ten arms (at least ancestrally) and were probably much more squid-like after all.

Little was still actually known about these cephalopods’ soft parts, but some internal anatomy had at least been figured out by the early 21st century. Enigmatic fossils known as aptychi had been found preserved in position within ammonite shell cavities, and were initially thought to be an operculum closing off the shell against predators – but are currently considered to instead be part of the jaw apparatus along with a radula

Tentative ink sac traces were also found in some specimens (although these are now disputed), and what were thought to be poorly-preserved digestive organs, but the actual external life appearance of ammonites was still basically unknown. By the mid-2010s the best guess reconstructions were based on muscle attachment sites that suggested the presence of a large squid-like siphon.

Possible evidence of banded color patterns were also sometimes found preserved on shells, while others showed iridescent patterns that might have been visible on the surface in life.

In the late 2010s the continued scarcity of ammonite soft tissue was potentially explained as being the same reason true squid fossils are so incredibly rare – their biochemistry may have simply been incompatible with the vast majority of preservation conditions.

But then something amazing happened.

In early 2021 a “naked” ammonite missing its shell was described, preserving most of the body in exceptional detail – although frustratingly the arms were missing, giving no clarification to their possible number or arrangement. But then just a few months later another study focusing on mysterious hook-like structures in some ammonite fossils concluded that they came from the clubbed tips of a pair of long squid-like tentacles – the first direct evidence of any ammonite appendages!

A third soft-tissue study at the end of the year added in some further confirmation that ammonites were much more coleoid-like than nautilus-like, with more evidence of a squid-style siphon, along with evidece of powerful muscles that retracted the ammonite’s body deep inside its shell cavity for protection.

Since ammonites existed for over 340 million years in a wide range of habitats and ecological roles, and came in a massive variety of shapes and sizes, it’s extremely likely that their soft anatomy was just as diverse as their shells – so there’s no single “one reconstruction fits all” for their life appearances. Still, at least we now have something less speculative to work with for restorations, even if it’s a bit generalized and composite, and now that we’re finally starting to find that elusive soft tissue there’s the potential for us to discover so much more about these iconic fossil animals.

Retro vs Modern #16: Uintatherium anceps

Discovered in the Western United States during the early 1870s, Uintatherium anceps was part of one of the earlier major conflicts in the the Bone Wars. Nearly 30 different scientific names were applied to various fossil specimens of this mammal in under two decades, and the taxonomic tangle wasn’t properly sorted out until nearly a century later in the 1960s when they were recognized as actually all being the same species.


1870s

Paleontologist Edward Cope considered Uintatherium (under the name “Loxolophodon”) and its close relatives to be proboscideans – part of the elephant lineage – due to some of the similarities in their anatomy. The first reconstruction of these animals showed this version, depicting elephant-like animals with downward-pointing tusks, short tapir-like trunks, and the multiple bony projections on their skulls speculatively shown as attachment points for large antler-like horns.

Cope’s rival Othniel Marsh heavily criticised that interpretation of Uintatherium, arguing that these huge mammals were instead a separate group within the ungulates named dinoceratans – although this wasn’t really as huge of a classification difference as it seems today, since at the time proboscideans were also considered to be ungulates!

The dinoceratan ungulate interpretation quickly won out, and for a while in the 20th century Uintatherium actually became a fairly popular and well-known prehistoric mega-mammal, commonly included in collections of cheap plastic “dinosaurs” and usually depicted as more of a knobbly-headed sabertoothed rhino.


2020s

In recent years the dinoceratans seem to have fallen into obscurity and some degree of paleontological neglect, with little modern work on the group and no major studies for the last couple of decades – although this might be starting to change.

Despite the early ideas about them being ungulates, the evolutionary relationships of dinoceratans have become much more murky over the last century or so. Due to different elements of their anatomy being highly convergent with various other mammals it’s easy to find “false positives” in morphological comparisons, and they’ve been proposed as being connected to a wide variety of groups including “condylarths“, “insectivores“, rodents, and cimolestans. But some mid-2010s research suggests they were in fact ungulates after all, closely related to early South American forms like Carodnia – a lineage whose own evolutionary relationships are murky, but may have close affinities with modern horses, rhinos, and tapirs.

We now know Uintatherium anceps lived across the Western and South Central USA during the mid-Eocene, about 46-40 million years ago, at a time when warm wet climates extended up into the Arctic and lush tropical-style rainforests covered much of the continent.

It was similar in size and build to a modern white rhino, about 4m long (13′) and stood around 1.7m tall at the shoulder (5’7″). It had three distinctive pairs of “horns” on its forehead, snout, and nose, that were similar in structure to the ossicones of giraffids, probably covered in skin and hair rather than keratin. Its elongated canine teeth were protected by bony flanges on its lower jaw, and seem to have been a sexually dimorphic feature that was much more prominent in males.

It also had an oddly concave skull, with its forehead dipping inwards, and an unusually tiny braincase for its size. It probably wasn’t a particularly intelligent animal, but it didn’t really need to be – as one of the first types of herbivorous mammal to get truly huge in the early Cenozoic, a fully-grown Uintatherium probably had no natural predators at all.

Retro vs Modern #15: Dimetrodon limbatus

With its prominent sailback Dimetrodon is one of the most iconic prehistoric animals – and one that still frequently gets mistaken for a dinosaur, despite being closer related to modern mammals.


1870s-1980s

The first known Dimetrodon fossil was an upper jaw fragment found in Canada in the 1840s, but at the time this specimen was thought to represent a dinosaur. It wasn’t until the late 1870s that species like Dimetrodon limbatus (initially called Clepsydrops limbatus) from the Midwestern and Southern United States were recognized as belonging to a much older and different group of animals given the name “pelycosaurs“.

While some paleontologists did propose pelycosaurs as being ancestral to mammals quite early on, for several decades the prevailing view was actually that they were an ancient branch of rhynchocephalian reptiles closer related to modern tuataras. From the 1910s onwards pelycosaurs were finally linked back to mammals, with their similarities to the therapsids placing them as early members of the synapsid lineage – although all these early mammal-relatives were still considered to be derived from reptiles, and “mammal-like reptile” became a commonly-used term for them. 

As a result reconstructions of Dimetrodon during this time period usually depicted a highly reptilian and heavily scaled lizard-like animal, with a sprawling belly-dragging pose, protruding crocodilian-like teeth, and a highly shrink-wrapped sail on its back modeled on those of some modern lizards. Some earlier images also showed a short stumpy tail, since Dimetrodon‘s longer tail proportions weren’t confirmed until the 1920s.


2020s

During the late 20th century new classification techniques led to the messy concept of “reptiles” being properly redefined as sauropsids, and synapsids being recognized as an entirely separate non-reptilian lineage of amniotes. Along with new studies and discoveries this has resulted in our understanding of Dimetrodon changing a lot in the last few decades, moving away from a heavily reptilian interpretation and instead letting it be its own weird “protomammal” thing. 

We now know there were at least a dozen different species of Dimetrodon living during the early-to-mid Permian, about 295-272 million years ago. Most of them are known from North America, but an additional species discovered in Germany suggests this genus ranged further across Pangaea than previously thought.

Dimetrodon limbatus was one of the larger species, about 3m long (10′), and like other members of the genus it had a tall narrow skull with high-set eyes and two distinct types of teeth in its jaws. The structure of its nasal cavities suggest it had a good sense of smell, and like the related synapsid Ophiacodon it may have had a closer to “warm-blooded” metabolism than previously thought.

It would have had a very poor sense of hearing, however, and probably didn’t even have any visible ears on its head. It may have been functionally deaf to air-borne sounds entirely, only able to detect vibrations by pressing its lower jaw to the ground.

No skin impressions are known for Dimetrodon. Scaly reptile-like skin has been found on varanopids, a group traditionally classified as very early synapsids – but some recent studies have suggested they were actually part of the true reptile lineage, so their extensive scaliness probably doesn’t apply to synapsids like Dimetrodon after all. There is some possible evidence of rows of square or rectangular scale-like scutes on the underside of the belly and tail in pelycosaur-grade synapsids, but otherwise the next-closest known synapsid skin comes from the distantly-related therapsid Estemmenosuchus, which seems to have had smooth glandular skin similar to a hairless mammal.

The characteristic back sail, formed by highly elongated neural spines on the vertebrae, is now thought to have been covered in a different pattern of soft tissue than older reconstructions depicted. The texture of the bone along the spines’ length shows that at the base they were deeply embedded in the back musculature, then further up they were covered by skin webbing, but then at the tips they may actually have been unwebbed and free-standing, giving a much spinier profile.

While the sail was traditionally assumed to be used for temperature regulation, more recently this has started to seem less likely. The sail doesn’t seem to have been quite as well-supplied with blood vessels as previously thought, and there’s a lack of direct correlation between sail size and body size in different Dimetrodon species and age classes. Instead this structure may actually have been used for visual communication and display, and could therefore have been quite flashy and brightly-colored.

Fossilized trackways also suggest that Dimetrodon didn’t move with a low lizard-like sprawling gait but instead with something more like a crocodilian “high walk”, with its limbs much closer to upright. It was probably a fairly active terrestrial predator and would have eaten a wide variety of other smaller Permian animals, with its teeth having been found in association with the remains of the amphibians Eryops and Diplocaulus and the freshwater shark Xenacanthus.

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.