Tag: theropod

Strange Symmetries #14: The Tooth About Baryonyx

Almost all toothed theropod dinosaurs had exactly four teeth on each of their premaxillary bones, the paired bones at the very tip of the upper snout.

A diagram of the various bones in the skull of Spinosaurus.
Spinosaurus skull by AS | Public domain

The semi-aquatic spinosaurids were an unusual exception to this with six or seven teeth per premaxilla – and one particular member of this lineage seems to have been just a little bit weirder.

Baryonyx walkeri lived during the early Cretaceous, around 130-125 million years ago, in what is now southeast England. About 9m long (~30′), it had distinctive enlarged curving claws on the first fingers of its hands, along with a long narrow snout with a “rosette” at the tip followed by a notch (a shape convergent with the jaws of modern pike conger eels).

And that premaxillary rosette had a strangely asymmetrical arrangement of teeth.

A closer view of the lineart for Baryonyx's premaxillary rosette. The six left teeth are indicated in pink, and the seven right teeth in dark green.

The left side had six teeth, and the right side had seven.

Why? We don’t know!

Baryonyx skull material is rare and fragmentary, so it’s unclear if this was actually a characteristic feature of the species or if the known asymmetric rosette just represents an unusual individual.

Natovenator

Halszkaraptorines were a group of small dromaeosaurids known only from the Late Cretaceous of Mongolia. They were odd little raptors with flattened snouts, long necks, and flipper-like arms – features that suggest they were specialized for swimming, making them the second known lineage of semi-aquatic non-avian dinosaurs after the spinosaurids.

This “duck-raptor” interpretation has been a little controversial since it was first proposed in 2017, but we’ve just gotten some more evidence for it in the form of an entirely new halszkaraptorine.

Natovenator polydontus lived in what is now the Gobi Desert in southern Mongolia, around 72 million years ago. The size of a small duck, about 45cm long (18″), it had jaws full of many needle-like teeth, a long flexible goose-like neck, and a streamlined body with a wide flattened ribcage convergently shaped like those of modern diving birds.

Although it had long strong legs, these don’t show much in the way of aquatic specializations and would have been used more for walking and running on land. Instead it may have used its flipper-like arms to propel itself through the water, like modern penguins or auks.

It probably had a lifestyle similar to modern mergansers, swimming and diving in lakes and rivers, and preying on fish, amphibians, and aquatic invertebrates.

It Came From The Wastebasket #17: Getting Ornithomimus In Order

The ostrich-like “bird-mimic” dinosaur Ornithomimus was named in 1890, based on some hand and foot bones from Late Cretaceous-aged fossil beds in Colorado, USA.

The first ornithomimid known to science, it was initially thought to be a ornithopod, but then a few years later more fossil material revealed it was actually a theropod – and then it spent some time classified as a “megalosaur” before ornithomimids were finally recognized as being coelurosaurs in the early 20th century.

And for nearly a century after its discovery it was treated as a wastebasket taxon for any similar-looking fossil material from North America and Asia, with around 17 different species named within the genus. One of these was split off into Struthiomimus in 1917, but it wasn’t until much later that the rest began to get sorted out.

A review of known Ornithomimus fossils in the early 1970s renamed a couple more species into the new genera Archaeornithomimus and Dromiceiomimus, and dismissed most of the remaining species as dubious or invalid. Just two valid species now remained: the original Ornithomimus velox from Colorado, and Ornithomimus edmontonicus from Alberta, Canada.

An illustration of Ornithomimus, an extinct feathered dinosaur. It has a a small beaked head atop a long slender neck, two wing-like arms with three clawed fingers, long ostrich-like legs, and a counterbalancing tail with longer feathers towards the tip.
Ornithomimus edmontonicus

Since then opinions have gone back and forth about some of the other Ornithomimus species. For a while Dromiceiomimus was merged back into Ornithomimus, but more recently it’s been found to have distinct limb proportions and was probably actually a separate genus after all. Another species that’s usually considered to be part of Struthiomimus is also sometimes instead classified as an Ornithomimus instead.

Really all of the North American ornithomimids are in need of a modern taxonomic revision – especially since Ornithomimus edmontonicus shows enough anatomical variation that it might actually represent a species complex of multiple very similar forms, which might get split apart in the future if anyone can figure out how to reliably distinguish them.

It Came From The Wastebasket #12: Coelurosaur Confusion

Historically Coelurosauria was the counterpart to the Carnosauria, with both of them representing two major lineages of theropod dinosaurs.

Created as a group in the early 20th century, coelurosaurs quickly became a dumping ground for all small-bodied theropods – including coelophysoids, compsognathids, ornithomimids, oviraptorosaurs, dromaeosaurids, and troodontids– and for a while this wastebasket taxon also included the large-bodied ceratosaurids and tyrannosauroids, before they were moved over into the carnosaurs.

But during the 1960s and 1970s this arrangement began to break down. A better understanding of groups like dromaeosaurs revealed a confusing mixture of traditional “carnosaur” and “coelurosaur” anatomical features, and paleontologists struggled to figure out where these sorts of theropods actually fit in.

The development of cladistic methods from the 1970s onwards led to efforts to clean up the coelurosaur wastebasket, trying to figure out a more accurate version of these animals’ evolutionary relationships. After briefly collapsing Coelurosauria down to just coelophysoids and “coelurids“, the growing recognition of modern birds as living theropod dinosaurs eventually resulted in the group being properly redefined in the 1980s as “birds, and all theropods closer related to them than to carnosaurs“.

An illustration showing four examples of coelurosaurs, theropod dinosaurs closely related to birds. One the left is Citipati, a bird-like feathery oviraptorosaur that has a cassowary-like crest on its head, a short beak, a long neck, feathered wings, long slender legs, and a short tail with a feather fan at the end. It's mostly colored black and white, with bright blue and yellow face markings and small eyespots on its wing and tail feathers. At the top is Albertosaurus, a tyrannosaur with short bony crests above its eyes, tiny two-fingered hands, long bird-like legs, and a long thick counterbalancing tail. It's colored with a blotchy striped pattern of yellow, red, and dark brown, with bright blue on the crests over its eyes. On the right is Yi, a small bird-like scansoriopterygid with a fluffy feathery coat, four long tail feathers, and large membranous wings supported by a bony extension from its wrist that make it look like a dino-bat or a wyvern. It's colored brownish-grey with a yellow snout and striped markings on its neck, wings, and tail feathers. At the bottom is Sinosauropteryx, a compsognathid with a typical theropod body plan – triangular head, S-shaped neck, three-clawed hands, bird-like legs, and a long tail – but it's covered in fluffy feathers which are especially bushy on its tail. it's colored ginger-and-white, with a black raccoon-like mask marking over its eyes and a stripey tail.
Clockwise from the left (not to scale): Citipati osmolskae, Albertosaurus sarcophagus, Yi qi, Sinosauropteryx prima

The coelophysoids were finally removed entirely, reclassified as a much earlier branch of theropods – but quite a few of the other groups from earlier concepts of Coelurosauria survived this reshuffling, with the compsognathids, ornithomimids, oviraptorosaurs, dromaeosaurs, and troodontids all proving themselves to have really been closely related the whole time. Meanwhile the tyrannosauroids were brought back in, along with the therizinosaurs, alvarezsauroids, and a whole bunch of paravian and avialan lineages.

(Megaraptorans might belong somewhere in the coelurosaurs, too – possibly being tyrannosauroids – but their classification is currently being disputed.)

It Came From The Wastebasket #07: Carnosaur Carnage

Carnosauria was originally named in the 1920s as a grouping for all of the large-bodied theropod dinosaurs known at the time.

For much of the 20th century it was used as a general wastebasket taxon collecting together all big carnivorous forms – including allosaurids, carcharodontosaurids, megalosaurids, spinosaurids, ceratosaurids, abelisauroids, and tyrannosaurids – and for a while it even included a species that later turned out to be closer related to crocodiles than to dinosaurs.

An illustration showing four different carnosaurs: Asfaltovenator, Torvosaurus, Giganotosaurus, and Baryonyx. They're all bipedal carnivorous dinosaurs with small three-clawed arms, bird-like legs, and long counterbalancing tails, but they vary in size, coloration, and most notably head shape. Asfaltovenator and Giganotosaurus have fairly typical boxy theropod heads, while Torvosaurus has a longer snout and Baryonyx has slender crocodile-like jaws.
From left to right: Asfaltovenator vialidadi, Torvosaurus tanneri, Giganotosaurus carolinii, & Baryonyx walkeri

But then cladistic analysis in the 1980s and 1990s revealed that some of these theropods weren’t actually closely related at all. Carnosaurs weren’t a natural lineage but instead were highly polyphyletic, with the physical similarities between them seeming to be more due to convergent evolution than direct shared ancestry.

Some carnosaurs were split off and reclassified as more “primitive” types of theropod, while the tyrannosaurs were placed much closer to birds with the coelurosaurs. The remaining “carnosaurs” were just the allosaurids, carcharodontosaurs, and their closest relatives, and some paleontologists now prefer to use the name Allosauroidea for this group to distance it from the previous wastebasket mess.

…But Carnosauria might not be done just yet.

A screenshot from "Phineas and Ferb", with the two main characters in a room lit up by an offscreen disco ball, with one grabbing the arm of the other. Text below them reads "Dude, we're getting the band back together!" Both of their heads have been photoshopped into those of Megalosaurus and Asfaltovenator.

The discovery of Asfaltovenator in 2019 complicated matters once again, with a mixture of anatomical features linking it to both the allosauroids and the megalosauroids (megalosaurids, spinosaurids, and their relatives) – suggesting that these two groups might actually have been closely related to each other in a single lineage after all.

This would potentially return Carnosauria back to something surprisingly close to its original definition, with the various megalosauroids now forming an evolutionary grade leading to the allosauroids.

It Came From The Wastebasket #05: The Trouble With Troodon

Troodontids were small bird-like theropod dinosaurs, lightly built with slender legs and sickle-shaped “raptor” claws on the second toes of their feet. They had fairly big brains proportional to their body size, rather like modern birds, and their large forward-facing eyes had good depth perception. Owl-like asymmetrical ears in some species gave them a very keen sense of hearing, suggesting they may have been nocturnal hunters using sound to pinpoint the location of small prey.

The original specimen of the namesake of the group, Troodon formosus, was a serrated tooth discovered in the 1850s, about 77 million years old and originating from the Late Cretaceous Judith River Formation fossil beds in Montana, USA. It was so little to work with that it was initially mistaken for a lizard tooth, then during the 20th century it was recognized as belonging to a dinosaur and spent time classified as a megalosaurid, then a pachycephalosaur, then finally as a small theropod similar to the Mongolian Saurornithoides.

In the late 1980s it was merged together with multiple other troodontids (including Stenonychosaurus of speculative “dinosauroid” fame), and since Troodon had been the first of all of them to be named it took priority as the genus name.

And then for a while every single Late Cretaceous troodontid specimen from North America was also lumped into Troodon, turning it into a wastebasket taxon.

An illustration of five troodontids standing in a circle facing each other. They're all very bird-like feathered dinosaurs with vaguely owl-like faces, reddish-orange and dark brown plumage, and white spots and bars on their longer wing and tail feathers. There are minor variations in their color shades and markings, but otherwise they all look incredibly similar to each other. The overall composition of the image is similar to that of the "Spider-man pointing at Spider-man" memes.

The problem was that all these troodontids came from locations separated by thousands of kilometers and millions of years of time, and it’s unlikely that they all actually represented just one single species. But they were only known from rare fragmentary remains, making distinguishing them from each other difficult, and the original Troodon tooth didn’t really have any distinctive features either – it turns out most troodontid teeth all look exactly the same!

It was becmoning increasingly dubious whether Troodon was even a valid name at all, and during the 2010s several paleontologists began trying to sort the mess out. The old names Pectinodon and Stenonychosaurus were revived, and some ‘Troodon’ fossils were also split off and given completely new names, becoming Albertavenator and Latenivenatrix*.

* Although Latenivenatrix might not actually be distinct enough from Stenonychosaurus to justify having a separate name.

As of 2022, Troodon itself is now in a sort of taxonomic limbo, with some paleontologists abandoning it as a dubious name while others are still arguing in favor of continuing to use it. The name could potentially be properly rescued if the original tooth can be clearly linked to better fossil material, letting Troodon take over priority again from one of the other better-established troodontids, or by defining a new type species similar to what happened with Iguanodon.

…But with how incredibly generic that tooth is, both of those options would be very difficult.

Rajasaurus

Abelisaurids were a group of theropod dinosaurs characterized by short snouts, bony ornamentation on their skulls, tiny stiff arms, and stocky legs. Known mostly from the southern continents of Gondwana, they were the dominant predators in these regions and are thought to have been specialized hunters of titanosaurian sauropods.

Rajasaurus narmadensis lived in what is now western India during the Late Cretaceous, about 67 million years ago. Around 7m long (23′), it had very rough-textured thickened bone on the top of its snout, along with a short rounded horn on its forehead that was probably used for display or headbutting behaviors.

India at this time was an isolated island continent located off the east coast of Africa, and Rajasaurus‘ ancestors probably island-hopped across from then-nearby Madagascar – where its closest known relative lived, the very similar-looking Majungasaurus.

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.