Wednesday, August 26, 2015

Palaeo-Study: What's with all these feathery theropods?

((Author's Note: As my debut post here, I'd like to make my own little series called Palaeo-Study; where I will discuss more serious topics that wouldn't fit into a Paleo Profile, but deserve their own posts. As such, this is not going to be a short post. Enjoy!

As many are likely aware, palaeontologists have considered birds to be direct descendants of the theropods for a very, very long time. This is, obviously, because of the taxon known as Archaeopteryx ("first wing"), which was first described in 1861 by Christian Erich Hermann von Meyer.

Archaeopteryx reconstruction showing what we know about the animal.
Credit for the image goes to Nobu Tamura.

This small dinosaur has caused a bit of a cladistic controversy for decades; palaeontologists have been split on if it was a true avian, albeit the most primitive of them, or if it was a highly bird-like maniraptoran. Currently, consensus seems to be on the former, though it remains under debate.
The genus has also played a pivotal role in solidifying the concept of evolution as the palaeontological consensus; as it has both features of more advanced true birds (pennaceous feathers and a mostly-feathered body) and traits of non-avian maniraptorans (teeth, clawed fingers).

However, for as pivotal as this genus is, this also means that it has caused a fair bit of controversy, especially for those who do not believe in abiogenesis or evolution as the origin of life. An animal with traits of two types that these people distinctly separate disrupts their faith; and they either say it's a bird and nothing more or, in more extreme cases, call it a hoax fossil (likely in reference to the actual hoax fossil that was called "Archaeoraptor"). There are multiple factors that separate the two, however;
  • Archaeopteryx was found in Germany, while "Archaeoraptor" was found in China, a location known for it's instances of bootleg or faked fossils.
  • Archaeopteryx is known from multiple well-preserved specimens that clearly could not have been Frankensteined together. "Archaeoraptor" was made of multiple, quite damaged specimens that looked as if they were patched together.
  • Archaeopteryx was Late Jurassic, while "Archaeoraptor" is just an assortment of Cretaceous animals stitched together.
As for other feathery theropods, ones that people often bemoan and ridicule are Velociraptor and Tyrannosaurus; both due to bias. Feathers get commonly associated with things like chickens, which are considered derpy, stupid meals on legs. Meanwhile, scales get associated with dragons, which are seen as awesome, powerful beasts. The comparisons are unfair, obviously; why compare a mild bird like a chicken to a powerful monster like a dragon?

Again, the answer is bias; people want to "show" how ridiculous feathers on dinosaurs are, and so say that it makes them look like giant chickens instead of badass prehistoric dragons. But this isn't the case; a fully feathered Tyrannosaurus running at you is always going to be just as scary as a scaly one doing the same, because while we may say we have a preference, the fact is that our instinct will tell us what to do regardless of the animal's integument. This is also why people find bears scary when one runs at them, but not when looking at photos; it's the fight-or-flight response in action.

A good example of this sort of mental conditioning is Jaws, and the impact it had on sharks in the public eye. Jaws was a masterful horror movie, but it inadvertently caused a wave of fear-mongering that has yet to subside, and caused many to vilify sharks. The same is, in some manner, true in this instance; people fear-monger that feathered dinosaurs look "stupid" and "not scary", and thus they aren't immediately profitable, so movies don't make them look cool and scary, rinse and repeat ad infinum

To put it another way...if it was actually happening to you, you wouldn't care about how feathered-up that T.rex was, you'd just want to get as far away from it as possible. Feathers are not inherently "less scary" than scales; it's just people are conditioned to think they are. Popular culture certainly doesn't help the image, either; when what Hollywood considers "good" is a good 5-10 years behind what we'd find acceptable, that poses a big problem to scientific accuracy (then again, nobody in Hollywood seems to give a brontosaur's backside about that anyways... :p). 

In terms of phylogeny, we know 100% that most all coelurosaurian theropods had some amount of feathering. How extensive it was varies, but all known coelurosaurs have feathers; this is undeniable fact. For example, we know Velociraptor had pennaceous feathers on it's arms (that is, arms with a central shaft, like birds) due to quill knobs left on the forearm of specimens, was but the size of an ocelot...and was, to be blunt, quite stupid and couldn't run fast at all; but of course, popular culture would have you think they were leathery, lightning-quick, man-sized superpredators smarter than whales, dolphins and some primates. And that's not even getting into the other issues that movie has.

All coelurosaurs, including tyrannosaurs, had feathers. This is not for debate, it's pretty much confirmed at this point. Technically, feathers may spread back into the base of Archosauria (or at least Avemetatarsalia), as modern alligators carry the base genetics for creating feathers in their DNA, just rendering them into scutes instead. This suggests feathers (or at least some kind of filamentous structure) are a basal archosaur trait, and that crocodylians shed them (turned off the gene) as they became more adapted to a semi-aquatic lifestyle, and likely closes the notion that the two structures are separate genes. In essence, crocodile scales....are really very primitive forms of feather.

So really, this could just mean all dinosaurs have the possibility of possessing feathers, as they would all have to have beta-keratin. If they did is uncertain, that they could is. And it's not like feathers are detrimental; after all, feathers give our fine dromaeosaur friend the power to run up walls and lets him pin his prey and eat it alive; surely, those can't be considered "weak" and "dumb" abilities?
So chin up about Velociraptor being enfluffled! It just makes it so that you literally have no escape from it other than shooting the darn thing.

Or running quickly.

Either way, it's more dangerous than the roid-rage super raptors we see in pop culture in terms of terrain adaptability. Not even the walls are safe!

Editors' note: It is important to remember that rarely anything in the field of Paleontology can be considered absolute. Velociraptor was almost certainly feathered, but the debate whether or not T. rex was remains controversial. For evidence in favor of scaled tyrannosaurs, refer to here (check under 'Yutyrannus the tyrannosaur?' and 'The Feather Scale Dichotomy')  -

Author's reply: While it's certainly plausible that more advanced tyrannosaurids did undergo some amount of feather reduction, the benefits of feathers in a thermophysical sense is too much to suggest that all or even most of their feathers became reticulae. The most accurate conservative depiction of the genus is the newly revamped design in use by the game Saurian, which can be seen here.

However, evidence is leaning towards a subtropical climate for Hell Creek, and an average temperature not that far from the Yixian's, which may suggest that either Hell Creek had a consistent cold period or that it was overall cooler than we've predicted. Even if it was subtropical, more feathers on the animal make it more effective at thermoregulation than an unfeathered animal. I may decide to make a post showing how common arguments for naked tyrannosaurs are flawed sometime in the near future.

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