Updated: Oct 11, 2022
So did dinosaurs really have feathers? The answer is, well, yes...and no!
This isn't something I can imagine is a new revelation by now. The question 'did dinosaurs have feathers?' has long been theorised, then discovered and then connected to their descendants, the birds.
A few home truths
But that still hasn't stopped it from being a hot topic of debate since it was first suggested, namely because (I believe) the outdated versions of dinosaurs is what has captured the imagination of the masses and what so many cling to in order not to 'ruin' their childhood memories. I get it! I fell in love with dinosaurs from a very young age and I have very clear memory from when I was six years old in which I scoffed at one of my dinosaur books which depicted a Velociraptor with a slight mohawk of feathers, even though the book said that was what scientists thought it had. I didn't want what I'd fallen in love with to change. Little did I know that irrefutable evidence would turn up that Velociraptor had much more than a mohawk of feathers:
Of course I love the idea of feathered dinosaurs these days. If anything I think it makes them easier to imagine being real. But I digress, the fact of the matter is (without a nicer way of putting it) that science doesn't really care what you or I think. It doesn't care what fond memories you have from childhood, or what you think looks cool or scarier. It just deals in facts and evidence.
Sorry if that sounded harsh, but that band aid had to be ripped off...
Feathers vs scales
"But dinosaurs are reptiles and reptiles don't have feathers!" I hear you say. Well, firstly birds are actually scientifically classed under the reptile umbrella. In fact, dinosaurs are still alive today as birds are scientifically classed as dinosaurs. Secondly, the thing about feathers is that they are not mutually exclusive to birds, nor are scales to other reptiles. In fact, feathers are derived scales, they have simply evolved into more of a net structure than a solid mass. You'll even find scales that have reverted back from feathers on birds' feet. There are also different feather types, ranging from flight feathers to downy 'fuzz'. This is what gives a furry appearance on many dinosaur depictions.
Here's the real kicker of this post: some dinosaurs had feathers, some dinosaurs definitely did not and others...well who knows? Feathers are an ancestral trait in dinosaurs, much like hair in mammals. Even blue whales and dolphins have one or two tiny hairs on their bodies. By this logic, it's possible that ALL dinosaurs had feathers, but there are enough exceptions to that rule to call it into question. So which dinosaurs had feathers? Let's find out...
Let's get the biggest one out of the way first. Theropods (the two legged dinosaurs) are a very large group of dinosaurs and for some we have proof of feathers. Some, like birds, we've seen with our own eyes, others, such as dromaeosaurs (the group that includes what people typically think of when they hear the word 'raptor', like Velociraptor, Utahraptor or Deinonychus) have shown fossil evidence, such as integument impressions on the surrounding rocks, or quill knobs observed in the bone itself.
On the opposite end you also have theropods that almost definitely had not a single feather on their body. Take Carnotaurus sastrei, for example, who's yielded many skin impressions from all over the body showing a fully scaly dinosaur. By proxy, this could also mean that most other abelisaurids were fully scaly. But....
Then there is the group in between (i.e. most non-avian theropod dinosaurs) in which we can only really guess. Take the Tyrannosaurs, for example: feathers are ancestral especially to this group, as one of its most basal members, Dilong paradoxus, was found with evidence of feathers. Logic would suggest, therefore, that all members of the group inherited the trait and examples such as Yutyrannus huali (which literally translates to beautiful feathered tyrant) support that logic.
But then we look at the main man himself, Tyrannosaurus rex, who was the subject of the feather debate for years but was recently found to have been almost completely covered in scales! Now, ancestral traits are hard to shake off and the Tyrannosaurus rex skin impressions didn't show the WHOLE body, but its distribution was across enough bits of the body to suggest that it was mostly scaly.
If you ask me, it still could have had feathers, but they may have been very small quills maybe running along its back and almost not noticeable (much like hair on the aforementioned whales and dolphins). So don't worry, Tyrannosaurus rex is not a big fluff-ball and was mostly scaly. In summary, theropods have shown the most variety in integument with regards to fossil evidence, so we would have to take each species as it comes and with a ...maybe?
Sauropods (the long neck dinosaurs) are another widely discussed topic in terms of appearance. There could (and just might) be an entire blog post dedicated to this topic alone, trunks, neck flaps and all! But this is just about did dinosaurs have feathers. In short, sauropods were dinosaurs that were most likely almost completely scaly. Many skin impressions and even preserved skin have been found from various groups, suggesting a lack of feathers. So, though it's a minor possibility that they also had some minor quills or other tiny feather integument, it's not likely.
Ceratopsians (the horn-faced dinosaurs), are an interesting group. You may have seen the odd interpretation with these tail quills:
This has, again, been found to have been an ancestral trait. A little dinosaur named Psittacosaurus osborn yielded an amazing find. A specimen was found to not only have some melanin cells intact (meaning it is now known what colour the dinosaur was), but also tail bristles:
It is thanks to this feature that paleontologists have speculated that all ceratopsians have this trait due to the fact that Psittacosaurus is in fact a basal ceratopsian. This isn't to say they all had this feature for definite, however, it does seem likely the feature was present in some shape or form. Apart from this, all evidence and skin impressions seem to show they were otherwise scaly.
When it comes to whether or not the group that included the 'duck-bill' dinosaurs, it is another case of 'no direct evidence, but seems likely'. A basal ornithipod named Kulindadromeus showed evidence of a feathery 'fuzz' covering scaly plates. Very strange integument indeed, however, it was a basal ornithipod, meaning all features seen on it were likely to have been passed on to all other ornithipods to some extent or another.
Having said that, we do have many other skin impressions from this group as well as even a mummified hadrosaur! These impressions, from various parts of the body, have shown only scales thus far...
Here is another group that has yielded a 'mummified' dinosaur! A nodosaur (which is a type of ankylosaur) known as Borealopelta markmitchelli, was discovered in 2011 in which almost the entirety of its armour was preserved.
As you can see, the armour preserved shows no feather covering, which makes sense. Ankylosaurs are famous for their armour, being nature's most efficient tank. The highly dense armour (which even extended to their eyelids!) left little room for any feathers. The plates themselves were actually osteoderms, a type of bone that actually grows in the skin and are seen in today's crocodilians. Since the bone was growing through so much of the skin, it wouldn't have any room to grow feathers as well as that. This is one we can almost definitely say 'no' to!
The group known as stegosauria from the Jurassic are very close relatives of the ankylosaurs, with them both belonging to the clade of thyreophora. While stegosaurs are not direct ancestors of ankylosaurs, they most certainly are descended from the same armoured group as ankylosaurs. None of these groups have shown any evidence of feathers, nor would it make sense for them to due to the presence of the osteoderms. Skin impressions have also been found in a wide enough range of placements from the bodies to confidently say that they were scaly.
There isn't a huge amount on pachycephalosaurs integument, with the skin impressions being mostly from the head region, showing scales and horn ornamentation. From what we can tell, there's nothing to say they had feathers, however, they were very close relatives of the ceratopsians, so it is completely feasible for them to have had quill-like structures somewhere along their bodies.
Ok, not classified as what a dinosaur is, but they are very close relatives who are synonymous with dinosauria. Not only that, but their integument definitely means they're worth mentioning. Almost all pterosaurs have shown evidence of a fuzz covering their bodies and most of their head. The filaments that make up this fuzz are known as pycnofibers. Pycnofibers look, at a glance, like mammalian hair, however, they are actually made of the same material as feathers. This is interesting because pterosaurs diverged away from the dinosaurian group, but are not part of it, meaning they share a common ancestor.
So did dinosaurs have feathers? The conclusion...
So, there you have it! Some dinosaurs were definitely feathered without any shadow of a doubt, such as certain theropods. However, others were most definitely not, like the ankylosaurs. Given this variety, it's safer to not assume feathers or scales for any dinosaur without direct evidence, as we simply don't know how weird and wonderful these animals were.
However, we mustn't forget the pterosaurs in all of this. As stated above, they diverged away from dinosaurs and share a common ancestor with them, having shown clear evidence for their own type of feathers. From this, we can draw two possible conclusions: that they both evolved these structures separate of each other (something known as convergent evolution) and the dinosaurs that lacked feathers simply never evolved them and kept the scales, or that they both inherited basal feathers from their common ancestor, the dinosaurs that lacked feathers actually reverted BACK to scales and feathers are much more ancient than we once thought.