It’s a spiel that I run quite frequently in a conversation – “What’s a dinosaur?” It also seems rather contrarian to what people have been taught in primary school, when everything extinct was labelled as a “dinosaur.” People seem to recognize why mammoths and giant ground sloths (hinthint for upcoming restorations) aren’t dinosaurs. It’s pretty easy. Dinosaurs are reptiles and most cenozoic megafauna were mammals.
But when it comes to the reptiles that lived together in the Mesozoic – what should we call a dinosaur? The answer is actually rather simple.
Dinosaurs are defined – in phylogenetic terms – as every animal that is descended from the most recent common ancestor between Triceratops and modern birds.
I made a quick mockup of what this looks like. The figure above is a phylogenetic tree with several representatives of major dinosaur groups. The large branch to the left consists of ornithischians, and the right branch consists of saurischians. These are the two sides of the “dinosaur” coin. Triceratops is commonly thought to be the most advanced (“advanced” = recent/”newest”, in our nomenclature) ornithischian, having evolved just around the time of the K-T extinction that wiped out non-avian dinosaurs. Some even claim it may have been the final dinosaur population to finally keel over during said extinction event. Modern birds are the most advanced saurischian dinosaurs, and they have survived to the present.
The most recent common ancestor is an animal that existed sometime in the Lower Triassic (~250 MYA). We don’t know what it is. We may never know what it is. All we know is that it existed, and from that animal (rather, population thereof) came dinosaurs as we know them. The split between ornithischians and saurischians happened not long after.
The animals further above – the Pteranodon and Mosasaurus – are representative of other reptile groups that existed during the Mesozoic. Pteranodon is more closely related to dinosaurs than Mosasaurus, as it falls under “archosauria.” We’ll discuss more about the relationship between archosaurs sometime in the future.
Typically, when kids (or adults acting like kids) pretend to be a dinosaur, they kind of hunch over and open their mouths wide and make guttural roars and slobber everywhere. Another thing they do is position their hands like this:
And that’s your typical “rawr I’m a dinosaur” stance, right?
Of course I’m here to crush dreams and ruin childhoods – it’s part of the mission statement. Dinosaurs actually never held their hands this way. Ever. Never ever. Their wrists would’ve had to break in order to achieve such a pose (or flap their wings, but we’ll get to that later). The easiest way to look at this is if we observe your run-of-the-mill theropod.
Placing your hands and feet in a pose that has your palms and soles facing the ground is called pronation. The stereotypical human emulation of a dinosaur features both pronated hands and feet. In dinosaurs that are emulating…well…themselves, only their feet are pronated. Their hands are non-pronated, meaning that they’re pretty much always ready to clap (tyrannosaurs and abelisaurs, with their tiny arms, are not part of the “able-bodied clapper” club).
The reason behind dinosaurs never evolving the ability to pronate their hands is unknown. With bipedal dinosaurs, it’s simply not necessary due to their preference to handle objects with their mouths and would use their hands to rake/slash. The really interesting thing, though, is that quadrupedal dinosaurs are also feature non-pronated hands!
Let’s look at Scott Hartman’s Triceratopsskeletal.
Dinosaurs walked in a digitigrade stance – meaning that they stood on their toes while a fleshy “sole” made of fat and other soft tissues made up the rest of the hand/foot for support (although it’s possible that some dinosaurs may have adopted a plantigrade stance – with their true soles against the ground – on occasion). This is true of the front and hind legs. We’ve established that dinosaur hind feet were naturally pronated, but what of the front?
Observing the Triceratops, we can see the arrangement of the fingers on the skeleton and my hastily-made top-down view of what the foot would look like if you cut through the leg. I’ve pointed out what would be the “palm” in animals with pronated hands, like humans, and notice how it’s still positioned to face the other hand and NOT the ground! Dinosaurs just didn’t have pronated hands, and evolution seemed to accomodate for this strange exclusion over their natural history.
That is, until the birds came along.
You should know by now, after a fairly long time of this being hammered down by paleontologists, that birds are dinosaurs – having split off from small theropods around the mid-Jurassic and possibly continued to branch off other ancestors through the remainder of the Mesozoic. You should also know, by just observation, that when birds fly, they hold out their wings – facing down.
One must wonder: “Wait. Charles. You just said that dinosaurs couldn’t pronate their hands!”
Yes. I know.
But look at how a bird flies. The only way the…”hands” pronate is with a fully-extended front limb to the sides. When a bird flaps, it then brings its arms inward and down, and the wings face one another once again. This movement of the entire arm to its maximum extension, laterally, is the only way that birds and some dinosaurs have been able to achieve pronation – not in the way that mainstream media and people imitating dinosaurs have depicted. More detail about musculature and wrist positioning is available, but I’m not a complete expert on such topics.
So – TL;DR
Dinosaurs can’t pronate their hands the way people think.
Quadrupedal dinosaurs still don’t have pronated hands – they walk on their toes.
The only way for dinosaurs to achieve a pronated hand posture is if they could stretch out their arms a sufficient distance to twist the wrist – and a limited amount had the musculature to do so.
Paleontology is an ever-changing field, as are all other areas of science. thepaintpaddock was conceived upon that notion. As technology and our wealth of knowledge increases, we’ll do away with outdated ideas.
Such is the case – twice, even – with Brontosaurus.
Discovered and named by Othinel Charles Marsh in 1879, Brontosaurus is one of the many dinosaurs uncovered during the “fossil wars” of the late nineteenth century (I’ll be sure to write up on that sometime soon, it’s interesting stuff). A number of the genera named and described during this period of time have since been either synonymized (as in “this animal and this other animal are actually the same thing”) or are remaining in limbo. Sometimes the material is too fragmentary to even confidently call it a dinosaur!
Dinosaurs were still very poorly understood in the time of Marsh and his peers. Though it was clear that these were hulking reptiles that have long since expired, there wasn’t much prior material to go on. In the name of good spirits, it was “make do with what you’ve got.” What Marsh had was a partial skeleton that lacked a skull, which was and still is the tell-all for paleontologists in distinguishing genera.
Deeming the animal too similar to a contemporary sauropod – Apatosaurus – the lack of available material led to the synonymization of the two genera. Brontosaurus excelsus and other Brontosaurus species were re-labelled as Apatosaurus excelsus and so on. What happened in the ensuing decades was a pure cluster%^&. “Apatosaurus excelsus” (and onlyexcelsus) still didn’t have a skull. Material eventually found to have belonged to Brachiosaurus and Camarasaurus were tried and failed to be assigned to this headache of an animal.
Light contentions from paleontologists were scattered about the remainder of the twentieth century in regards to the validity of Apatosaurus excelsus, though the consensus remained that Brontosaurus was never a separate genus…until 2015.
An extensive study of the entire sauropod family was conducted by Tschopp et al. last year, which found that the skeletal remains between the type species of Apatosaurus (sp. ajax) and A. excelsus to be too divergent to be from the same genus. In taxonomy and biology, a type species describes the “baseline” for the genus. Think of it as the anatomical qualifications to be that genus. A. excelsus had too many bones that did not match with A. ajax in terms of traits such as proportion, creating a reclassification of A. excelsus to…
Funny how that works, isn’t it?
Brontosaurus‘s fall and rise relied on the keen eye of scientists from the era of the Bone Wars and the twenty-first century. Both conclusions were made using the available material and observation techniques. That’s why, in science, being “right” is typically only a temporary victory.
Brontosaurus is discovered in the late-1800s.
There isn’t a skull. Back then, skulls were the primary (and are still the easiest) way to distinguish between dinosaurs. Scientists consider the skeletons between Brontosaurus and Apatosaurus are too similar to be separate, and synonymize all Brontosaurus species as Apatosaurus.
Fast-forward to 2015.
We know enough about dinosaurs to notice fine differences in bone structure. The bones between A. ajax (the type species) and A. excelsus are too different to be from the same genus.
A. excelsus is re-separated as Brontosaurus.
Until next time!
Note: Brontosaurus excelsus still doesn’t have a skull. We guess it looked pretty similar to Apatosaurus‘s, though. Yay for our MVP – phylogenetic bracketing!
She’s a beauty, isn’t she? The Spinosaurus restoration above is loosely based on a Goliath heron (most notably the rust-orange neck and head).
So, I promised a full blog post on Spinosaurus, and here it is. Known for stomping onto the big screen some-fifteen years ago, the villain of Jurassic Park III was, supposedly, a spinosaur. Boasting a huge body, amphibious tendencies, and usable arms, it served a replacement for the tested-and-true Tyrannosaurus. It even managed to kill a sub-adult bull rex in a short-lived battle, resulting in the spinosaur snapping the rex’s neck (we’ll talk about hand pronation and how that MK-finishing move can’t apply later).
Spinosaurus might’ve become a superstar in 2001, but we’ve known about this animal for a very long time. Discovered, described, and cataloged in the midst of the World Wars, the originally-found remains were destroyed in Germany. The largely-fragmentary findings afterward have been augmented by phylogenetic bracketing. A crocodilian snout, hook-like claws, and its pure mass have always given paleontologists a hint to its diet and lifestyle.
In 2014, a study on the morphology of Spinosaurus was launched by Ibrahim et al. The most surprising finding from the study was the size of Spinosaurus‘s hind limbs – they were laughably small. So small, in fact, that it was proposed that it might’ve lacked the ability to walk on land altogether. A follow-up by a different party in 2015 found the proportions to be too exaggerated, but the debate between Spinosaurus‘s bipedal locomotion (or lack thereof) continues to this day.
What we took away from this, as agreed by the scientific community, is that Spinosaurus displays numerous traits that point to a semi-aquatic lifestyle. Its hind limbs, though functional, were still much shorter when compared to other theropods. It had nostrils placed closer to the top of the skull. Oxygen isotopes in the teeth, when compared to other animals in the area, more closely resemble that of semi-aquatic animals than land-dwelling theropods.
The continuing research on Spinosaurus is a testament to the ever-changing face of paleontology. From bipedal, to ?, to ???, the more we understand about an animal, the more questions we make for ourselves. I just hope that the changes could slow down just a little so I can have a stable restoration on-hand.
Okay, well, allow me to explain myself. It was World Penguin Day not too long ago and I got the lovely idea to create a semi-fluffy Spinosaurus…with penguin color patterns. It doesn’t make too much sense to have king/emperor penguin yellow hues around the neck, but it certainly does look striking, doesn’t it?
Spinosaurus was a large theropod – possibly the biggest ever known – that spent most of its time in the water. Its hind limbs, laughably tiny (its legs were to it as arms were to T. rex) made it…awkward on land, at best. I restored it with webbed feet and a weird pseudo-fin on its tail to enhance its swimming power. The extremely tall vertebrae along the back formed a strange “M” shape instead of a semi-circle. It was also likely not thin. The bones wouldn’t have been visible in life, giving the structure more of a hump-like appearance.
I’ll make a short essay on the voyage of Spinosaurus from weird Dimetrodon-a-saurus to the amphibious monstrosity it is today (upon completion of a more serious restoration).
Before we begin, I’d like to point out a fun fact: Tyrannosaurus rex is often abbreviated as T. rex (and more often erroneously written as “T-rex”) and is one of two organisms, the other being Escherichia coli…E. coli, that are commonly known to laymen by their scientific abbreviations. One of the largest killers in history and one of the smallest, respectively.
If you’re reading this, you should have a rudimentary understanding of what a Tyrannosaurus is. T. rex was a large theropod dinosaur that lived in the later years of the Cretaceous, right up until the K-T extinction event some 66 million years ago. They pushed thirteen meters in length, four meters in height (at the hip), and probably maxed out at around 6,000 kilograms. Estimates on weight depend on who you talk to and the body composition configuration you’re most comfortable with. The 1.5-meter skull was capable of exerting 12,000 PSI. To put that in perspective, a big dog can put down 300 PSI with its jaws. The saltwater crocodile holds the trophy for the strongest bite force of all extant organisms at a whopping 7,000 PSI…which is still only a little bit more than half of T. rex‘s.
I appreciate Tyrannosaurus as arguably one of the most well-studied prehistoric animals…ever, really. Its only contender is none other than Triceratops, whose scattered remains rest buried all over the American midwest alongside that of Tyrannosaurus. If we owe the extensive studies done on rexes on their popularity as the dinosaur is another argument for another day, but we cannot ignore the amount of information we know about them.
Approximate average size
Some indication of sexual dimorphism
Growth trends & aging
…and we can’t ignore the amount of information that we can only infer or straight-up don’t have.
Locomotion extrema (i.e. max speed, whether it could sprint, etc.)
Sounds/colors/other soft tissue-dependent traits
How paleontologists attempt to skirt around some of the more…nuanced aspects of Tyrannosaurus‘ (and really any other extinct animal) biology is through something called phylogenetic bracketing. Consider the figure below.
Tyrannosaurus belongs in a subdivision of theropods called Coelurosaurs – which includes tyrannosaurs, dromaeosaurs, ornithomimids, extant birds, and so on. Phylogenetic bracketing is simply looking at the traits of relatives and ancestors of an organism to create a well-informed guess to fill in missing details (until we find direct evidence that either contradicts or supports standing inferences). From the list of unknowns above, we can only really derive conclusions about one detail: Integument.
Integument is, bluntly, body covering. Skin, scales, feathers, scutes, you name it. For decades, dinosaurs had been assumed to be scaly. That’s not exactly an incorrect assumption. From their discovery until the late twentieth century, evidence for any other covering besides scales was minimal if not nonexistent. The link between Archaeopteryx, birds, and dinosaurs was not yet fully understood, though we did know there was a relationship. It wasn’t until small maniraptors preserved in similar substrates as Archaeopteryx (i.e. Microraptor & co.) did paleontologists realize how common feathers were in theropods.
But Tyrannosaurus, the size of a school bus, along with other gargantuan predators of the Mesozoic, were kept completely scaled in life restorations. Once more, this wasn’t an erroneous assumption. So far, only small theropods had been found with hints of feather preservation – until the freak that is Yutyrannus was discovered in 2012. A tyrannosaur of a similar size to Tyrannosaurus (really only about ~3m of a difference), Yutyrannus is the largest dinosaur to have been preserved with direct evidence of bearing feathers. A dinosaur of comparable size to Tyrannosaurus – which belonged in the same family group, as well – wearing a coat of fluff? What does this mean for our favorite movie star?
With this new information, along with prior assumptions made from Dilong, T. rex being completely scaly is likely a thing of the past. Bear in mind that the quantity and placement of feathers on Tyrannosaurus will remain unknown until more direct evidence is found.
But, uh, I’ve only slightly opened this can of worms about phylogenetic bracketing and integument. Crocodilians have primitive feather production genes. Birds have feather production genes (duh). Birds and crocodilians,are archosaurs, meaning they share a common ancestor that gave rise to crocodilians, dinosaurs, and extant birds.
This common ancestor needed to have the feather production gene for this to happen.
All dinosaurs might’ve been able to grow feathers.