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Albertonykus's avatar

No More Feathered Terror Birds

I'm so tired of people giving terror birds feathers! There's no evidence they did! We should draw them with scales until it's proven they had feathers, because scales are clearly the default for anything that doesn't have feathers! There's no evidence they had eyeballs instead of empty sockets either, but I draw them with eyeballs because I enjoy contradicting myself! Besides, they lived on tropical grasslands and were so big they'd clearly overheat if they had feathers! Okay, I acknowledge the fact that every member of the oviraptorosaur + paravian clade that we have integument of has feathers, but I think terror birds deviated from their ancestors for... no good reason, really! They just look silly with them; they look so much scarier being scaly and reptilian, and the appearance of living things is clearly dictated by how scary or mean I think they look! Furthermore, all feathered dinos lived in Asia, and terror birds were from the Americas, so that means they didn't have feathers! Right?
If you check out the Wikipedia talk pages of any well-known deinonychosaur (Velociraptor, Deinonychus, and Utahraptor for most part), you'll invariably find some variation of the above. And most of them aren't even that intelligent.
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You can say though, that phorusrhacids were more likely to be feathered than non-avians, because terror birds are more closely related to modern birds than dromaeosaurs are. And we have more evidence that all modern birds are feathered, than we do all dinosaurs being like that.

The further back you go down the evolutionary tree, the less likely dinosaurs were to have feathers, if feathers are a derived trait.

I accept dromaeosaurs being feathered, but you can't just equivocate them with terror birds, evolutionarily speaking.
Albertonykus's avatar
That might be a reasonable assumption to make if we only knew of feathers in modern birds and had no relevant information regarding other dinosaurs. However, in this case we do know that extensive, bird-like plumage originated long before modern birds did. It's not a simple sliding scale in which the likelihood of feathers decreases at a uniform rate the further you get from modern birds.

At least in the group Pennaraptora (which includes both dromaeosaurids and modern birds), feathers are always found whenever we have direct evidence of skin covering. If any members of this group were unfeathered, they must have lost feathers from a feathered ancestor. There's nothing inherently impossible about that, but so far we have no evidence of it occurring in pennaraptors, and most speculative reasons for why they might have done so would apply equally well to dromaeosaurids and to phorusrhacids (or to other large, flightless birds such as dromornithids). We have no reason to think that dromaeosaurids were more likely to lose their feathers than terror birds were.

You are correct in the sense that we have a much larger sample size for modern birds than we do for other dinosaurs, but in science we work with what we've got, and as far as we can tell it's probably not a coincidence that we always find feathers in pennaraptors (especially when we also have evidence for largely scaly skin in other groups of dinosaurs).
A sliding scale is a reasonable assumption, given that evidence for feathers becomes more iffy the farther back you go, and the fact that more primitive feathered dinosaurs had simpler feathers, to the point that basal ornithischians have only been found with quills on certain parts of their bodies (implying that feathers and feather coverage didn't evolve in one fell swoop, and took time to evolve). Of course this isn't the only plausible assumption, but without further evidence, it's a reasonable one.

Also, the more derived a lineage becomes, the harder it is to re-evolve basal characteristics, due to phylogenetic inertia. It's not impossible, and has happened before, but it's less likely.
Albertonykus's avatar
It is not true that ornithischians have "only been found with quills on certain parts of their bodies". That is the case in Psittacosaurus, which is only one of three ornithischians known to have filamentous integument. The extent of filament coverage in Tianyulong is unknown beyond the fact that it had quills (though allegedly, there are undescribed specimens that show a quite extensive coat). Kulindadromeus, on the other hand, has a variety of filamentous structures (including branching filaments, not just simple quills) covering much of its body besides the tail, hands, and feet. That alone shows that there is not a simple sliding scale relationship between phylogenetic proximity to modern birds and feather coverage; if that were the case, we'd probably expect filamentous integument to be at most highly localized in all ornithischians. Instead, we find that at least some were quite heavily filamented, likely more extensively so than in some theropods (e.g.: Carnotaurus).

I agree that there's probably a general trend towards decreasing variability of feather coverage as we get closer to modern birds, but I see little reason to assume that the origin of Neornithes (modern birds) was a "magic threshold" where the likelihood of losing all feathers became negligible. Even if the likelihood of neornithines losing feathers was notably less than that of their immediate ancestors, it's at least as likely, given the information we have, that that threshold to negligibility had already been crossed long before their origin.

I'll grant that phorusrhacids are not a perfect parallel to dromaeosaurids. Very few analogies are perfect. However, most of the arguments I've seen trying to justify depicting dromaeosaurids without feathers are not based on phylogenetic inertia, but are equally applicable to extinct flightless birds for which we lack direct evidence of their integument.
About the "Sliding Scale", I didn't mean it the way you mentioned. I meant that the farther back you go, the lower the probability any given dinosaur will be feathered, and the lower the feather coverage in general. The relationship isn't completely linear, but the general trend exists.  Which you seem to be okay with now. I was wrong though, about no basal ornithischian having complete protofeather coverage.

By the way, Carnotaurus comes from a fairly basal theropod lineage, where no feathers have been found, which again, supports that trend.

I wasn't trying to imply that neornithines were a magic cut-off point, sorry if it came off that way. Only that they, being more derived than non-avians, are less likely to lose their feathers. Thus birds are less likely to lose their feathers than dromaeosaurs. Although it was probably wrong of me to nitpick on dromaeosaurs specifically, since even if they were more likely to lose feathers, that chance is still tiny, as you mentioned. Though it's not insignificant for earlier dinosaur lineages, many of which have not been found with feathers.
Albertonykus's avatar
That's fair regarding the sliding scale. Yes, Carnotaurus fits the trend when compared to other theropods, but not when compared to the fuzzy ornithischians (at least under the simplistic model I'd assumed). And indeed, it appears likely that dinosaurs more distantly related to birds had high plasticity in the types of integument they expressed, but this satire is not about early dinosaurs.

I am still not convinced that birds must be less likely to lose feathers than dromaeosaurids. Phylogenetic inertia does not mean that traits are less likely to reverse with passing time; it is simply the concept that the evolution of organisms is constrained by what their ancestors had. If anything, inertia on its own would favor retention of feathers in dromaeosaurids given that they almost certainly had fully feathered ancestors.

It wouldn't surprise me if, on average, we'd statistically expect to see that later members of a lineage have a harder time breaking out of those constraints than earlier ones, because they've had more time to accumulate mutations that might render such a change difficult or fatal. However, we can't infer on that basis that, for example, neornithines have a harder time losing feathers than enantiornithines, which in turn had a harder time losing feathers than dromaeosaurids, and so on. In practice, constraints can become "locked in" at any point in the evolutionary history of a lineage (potentially even simultaneously with the origin of a given trait). For example, the consistent presence of seven neck vertebrae in mammals appears to have been fixed essentially as soon as it appeared in the mammal line (and the few known exceptions to this are among modern mammals, not among their earlier relatives that diverged shortly after gaining this trait). In the case of feathers, that point could have been Neornithes, or Pennaraptora, or any point in between, or possibly even earlier.

Is it possible that dromaeosaurids were more likely to lose feathers than terror birds? Yes, of course. But in the absence of evidence either way, I don't think that's an assumption we can make.
"It wouldn't surprise me if, on average, we'd statistically expect to see that later members of a lineage have a harder time breaking out of those constraints than earlier ones, because they've had more time to accumulate mutations that might render such a change difficult or fatal."

This is exactly what I've been trying to say. On average, we expect modern birds less likely to lose feathers than their ancestors. I never said that all birds must follow this trend, just that the trend will be there and birds, in general, should follow it.

This is also an example of phylogenetic inertia - as species mutate, their chances of "going back" decrease as more and more mutations pile up to change the organism.

"Is it possible that dromaeosaurids were more likely to lose feathers than terror birds? Yes, of course. But in the absence of evidence either way, I don't think that's an assumption we can make."

I also never said this assumption was certain - only that it was reasonable, given the evidence we have. And it is a reasonable assumption to hold.
Albertonykus's avatar
I said that speaking in general, looking at all traits across all organisms, we might reasonably expect constraints on modifying a given trait to become "locked in" after the origin of said trait. However, I dispute that such a tendency means that there must be a trend for descendants to continuously become less likely to modify said trait compared to their ancestors, or that we can extrapolate such a trend to the evolution of all traits even if it did exist. Theoretically, a single mutation could be enough to hinder the reversion of a trait and future mutations could well have little to no further effect on that, in which case you'd see a sharp dip in the likelihood of reversion followed by a plateau, with no progressive decrease in likelihood. I'm sure other patterns are at least potentially possible, too. In other words, I doubt that we can assume the model of trait evolution you are presenting to begin with. If you know of any peer-reviewed studies that demonstrate otherwise, please feel free to share.
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Nuclearzeon2's avatar
So what if their smaller seriema relatives have feathers? We have no evidence of feathers in phorusrhacids, therefore that means they were scaly!
ffejgao's avatar
"Now I'm concerned on a number of levels."
PCAwesomeness's avatar…

I get this is a joke. Just needed to put that there.
Give feathers to all theropods unless it's a Carnotauurs, people. Besides that does not keep them from wrecking the s&!t out of you.
PCAwesomeness's avatar
Or any ceratosaurian.

Also, agreed.
Monstatronnn's avatar
thisis the best 
Hybodus's avatar
This is quite funny. I wonder why so many people are not willing to accept that many non-avian dinosaurs had feathers... We may not have direct evidence for every genera but people should use some common sense.
forkhead12's avatar
Most Retarded looking thing ever. All small Therapod dinosaurs looked retarded without feathers even when people give them lizard hides they still look really pissy.
Mesozoic0906's avatar
The most annoying Anti-feather opinion I ever met:
Feather doesn't look cool, so don't draw it.

Albertonykus's avatar
Agreed. Nature doesn't care whether you think it's cool or not.
Gojira5000's avatar
Am I a horrible maniraptor fan or does this guy look somewhat threatening even without feathers?

It would be hideously inaccurate and somewhat laughable, but It's beak still holds up it's threat, though.

It could be a decent movie monster, though.

"Attack of The Feather Snatchers!", anyone? :P
Albertonykus's avatar
Nah, you're free to like whatever you want, as long as you realize what's accurate.

Though the concept that any of my drawings can look threatening is new to me.
RajaHarimau98's avatar
I could not favorite this enough. Whenever someone says something like, "Give me proof Utahraptor had feathers", I just say "Give me proof Smilodon had fur and terror birds had feathers". :)
Albertonykus's avatar
Exactly. XD Thanks!
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