Wednesday, July 16, 2014

People Think Feathered Dinosaurs Don't Look Scary. They're Right.

This short article on io9 pretty well encapsulates an area of frustration for artists and scientists in the age of feathered theropods.
Ooh, I'm shakin' in my boots.
Photo by Simon Rumblelicensed.
The implication is, right from the title, that it's common knowledge most depictions of feathered T. rex are not cool. Feathered theropods are widely derided by the public because feathers make these scary reptilian monsters less scary. In a recent Facebook discussion, I took one of those "short pelt raptor" images to task for inaccuracy (you know, the kind that pays lip service to the idea of feathered theropods, but with the minimum possible change to the classic silhouette, with a cat-like short pelt rather than a bird-like poof of feathers engulfing the body). In my reply I kind of hypothesized that there's an evolutionary psychology* reason for our aversion to feathered theropods and our cat-like concessions to the idea.

As Andrea Cau has pointed out, paleoartists (myself included), consciously or not, often employ all kinds of subtle tricks to make feathered theropods look "cool". Leaving the face scaly and reptilian is a popular trick; his body might say "Big Bird", but his face tells you he means business. Face fully feathered? Introduce an eagle-like lowered "brow" or some kind of eyebrow analogue so his facial expression can look "mean". Make sure his mouth is open or he's prominently displaying his other weapons in a ninja-like fighting stance. And be sure if you make him colorful, use high contrast, red and black if possible, and light it so his face is in shadow--that way you know he's thinking evil thoughts. This might also allow you to add eye shine making the eyes look like demonic embers! (check back to the io9 article and see how many of these points that T. rex hits).

In the comments to the io9 article, there were the predictable bouts of resistance to the idea that T. rex could have had feathers at all. "It was too large! Large mammals don't have so much fur in hot climates!" The problem with comparisons to large mammals is that feathers are very different in structure from fur, and have very different insulating properties. Fur is mainly used to keep an animal warm, but thanks to the fact that feathers grown in adjustable, planar layers, and are better at trapping and regulating air flow, many large birds use their feathers to very effectively keep themselves cool by circulation while blocking the skin from absorbing direct sun. It may actually have been disadvantageous for a large animal to lose its feathers, especially if it lived in a hot sunny climate. The fully-feathered Yutyrannus was not significantly smaller than any but the largest T. rex. Most T. rex specimens fell short of the 6.8 tons estimated for the most gargantuan known adults like Sue, that is certainly not the species average size!

But, there was one comment that played right into my ego-psych hypothesis. The commenter basically stated that we know juvenile T. rex had feathers, but there's no reason to think adults kept them. Except even that premise is wrong. 
There is in fact zero direct evidence to support the hypothesis that T. rex juveniles had feathers, let alone that they had them and then lost them. It's simply easier for people to assume that a baby animal, which is supposed to be cute, had feathers, which we psychologically associate with cute animals. 

Are one of these things is not as scary as the other?
Illustrations by M. Martyniuk, all rights reserved.

It is actually less of a stretch (i.e. more parsimonious) to hypothesize that based on its phylogenetic bracket, T. rex had feathers and retained them throughout its life, than the hypothesis that T. rex was born with feathers, lost them because they became disadvantageous at some unspecified weight, then through some unknown developmental pathway replaced its feathers with the kind of thick, scaly skin it is usually depicted with and would need to protect itself from the sun/injury if it lacked feathers. But this convoluted thinking is easier for people to accept because T. rex is the king of all monsters, and monsters are by definition not cute.**

The sad fact is, T. rex may not have looked all that cool. I think John Conway and others have brought this up before. It, and many if not most other dinosaurs, may very well have looked really, really stupid to us. Nature doesn't care if an animal looks intimidating to a species that evolved 66 million years later in a completely different environmental context alongside a vastly different set of predators. Our brains are programmed to find mammalian and reptilian predators scary at least in part* because we evolved alongside these and our survival depended on it. We had no such pressure for most kinds of birds***, and maybe coincidentally, we find very few kinds of birds the least bit intimidating. We have to be told/shown that a cassowary is even capable of being dangerous, and people still constantly trot this out as a surprising fact, despite the fact that it has very few physical differences from a Velociraptor, other than being much larger

So, if your average Joe met a non-avialan theropod in real life, the reaction might be less like any of the raptor scenes in the original Jurassic Park and more like Newman vs. the cute, colorful, silly, hopping (read: bird-like) dilophosaur - bemusement leading to injury.

* I know evo psych is mostly made up of untestable just-so-storys. But it's still fun to think about.

** That's sarcasm. Tyrannosaurs were not monsters, they were plain old regular animals. A lesson people forget from the original Jurassic Park (probably because they're not actually depicted hat way in the movie, despite the fact that the characters talk about it).

***Raptors seem to be the exception. Probably because they preyed on early humans, and maybe also because of their mean-looking "eyebrows"?

Sunday, June 15, 2014

What Does T. rex Say?

T. rex holotype specimen. Photo by Scott Robert Anseimo, CC BY-SA 3.0.
It's an iconic scene in every dinosaur movie: the huge, conquering carnivorous theropod rears back and lets out a terrifying bellow. Sound effects artists spend huge amounts of time sampling vocalizations from various animals to create just the right mix to create an unfamiliar, otherworldly roar. And, of course, everybody knows that pterodactyls let out harsh, echoing, prehistoric sounding screeches.

But how close to reality are these sounds? Do we have any ways of using science to figure out what dinosaurs and other stem-birds may have sounded like? Do we have evidence that they made sounds at all?

Sunday, May 18, 2014

Review: Papo Archaeopteryx

Like many paleontology fans, I have a pretty big collection of little plastic dinosaur toys. Most of these I got when I was a kid and have held onto since, but every so often a nice looking model is released that is too cool to pass up. This new Archaeopteryx figurine from Papo was one of them.

Saturday, January 25, 2014

Oh, Hi, Bohaiornithids!

It's not often that we are introduced to a large new clade of stem-birds*, but a new paper by Wang et al. finds support for just such a thing among the enantiornithes. Named Bohaiornithidae, the family unites a few previously-known similar-looking opposite birds with two brand new species.

Phylogeny of Bohaiornithidae, modified after Wang et al. 2014.

Sunday, September 8, 2013

Iridescence in Simple Feathers - The Case of the Blue Troodon

Iridescent feathers in troodontids - possible? Image by Matt Martyniuk, all rights reserved.
(Supreme dino fans may recognize the pose even from this small clip...)
I've written a lot about the various ways feathers get their color in order to create some rough guidelines for paleoartists restoring feathered stem-birds. I recently had a quick discussion over at DeviantArt with one of the best currently-working paleoartists around, Emily Willoughby, over the plausibility of a blue Troodon. The illustration in question is here. Note that it has a few other anatomical issues that make it somewhat less than a fully accurate rendition, but is the coloration one of them? I wasn't sure, so I did a little extra digging to find out. As usual, this research is cursory and I welcome any additional input on research or details I may have overlooked.

Thursday, September 5, 2013

The Tale of the "Sail"

This version of the painting, "The Fin-Back Lizards" (background: Dimetrodon incisivus, foreground: Naosaurus claviger) by Charles R. Knight, appeared in H.F. Osborn's obituary for E.D. Cope, The Century Magazine (1897). Public domain.
Prehistoric tetrapods are fascinating to young and old alike in large part due to their often unusual features. We have duck-billed hadrosaurids, mammoths with huge curving tusks, horned and frilled ceratopsids, plate-backed stegosaurids, and, famously, a variety of prehistoric animals with sails on their backs, like the dimetrodonts.

Sails are often said to be present in other prehistoric animals, like ouranosaurs, spinosaurs, and arizonasaurs, but these are not the quintessential "sails" present in early synapsids like edaphosaurs and dimetrodonts. In the former, the neural spines of the vertebrae are very tall, but also broad and flat, as in normal vertebral columns. These probably anchored muscles, and at the very least supported a ridge of thick soft tissue, not just skin. In dimetrodonts and edaphosaurs*, on the other hand, the neural spines are not just tall, but thin, round, and strut-like. These aren't the kind of vertebrae that would be wrapped in muscle, and may have supported only a thin membrane of skin (I'm not aware of any actual direct evidence for a skin membrane sail, but correct me if I'm wrong).

During the late 1800s, the anatomy and relationships of the sail-backed synapsids was not yet well understood. In a situation weirdly parallel to the famous story about Brontosaurus, the first skeletons of what are now known as Edaphosaurus were found lacking skulls. A small herbivorous skull was actually found first, and given the name Edaphosaurus, but the connection to the sail-backed body was not made until later.  The whole saga of Naosaurus, as the headless body was named, was told by Brian Switek at Laelaps. In short, the headless body of Edaphosaurus was seen by E.D. Cope as being very similar to Dimetrodon, and Cope referred a skull to it which is know known to belong to the smooth-spined form rather than the knobby-spined form. When it was discovered that is was actually the small, herbivorous heads already named Edaphosaurus belonged to the headless body, the name Naosaurus was sunk.

Skull attributed to Naosaurus claviger (but now to Dimetrodon) from Cope 1888, public domain.

The thing that interested me most about revisiting this story was the whole history of the term "sail" itself. Why were these synapsids referred to as "sail-backs", a term that has since spread to any prehistoric animal with long neural spines?

Many people are aware of the early speculation that sail-backed synapsids used their sails to, well, sail. That is, to literally use their tall dorsal fins to catch the wind and move across water. Most people nowadays also think back on this idea as rather silly. The dorsal fin "sails" were, of course, parallel to the body, like the configuration of a sloop. However, unlike the speculative use of large crests as sails in some pterosaurs, which could at least move the head and neck to change the orientation of the supposed sail, poor dimetrodonts and edaphosaurs would be consigned to getting dragged more or less laterally across the surface of the water. At best, the undulating swimming motion of the torso would cell catch some wind, but the resulting constant change and undulating motion of the sail itself seems like it would make steering very difficult. (Nonetheless, I'm certain I've seen an artistic rendition of this behavior somewhere).

Switek says in his blog post the same thing I and everyone else tend to assume about Cope's sailing hypothesis, which is that Cope suspected "the long spines had a membrane stretched between them and could be used to catch the wind, just like a sail".

But, that's not quite right. It's true that Naosaurus translates as "ship lizard", named for Cope's sail-back hypothesis. But this hypothesis seems to have been specific to Cope's ship lizard, not to the (he thought) closely related Dimetrodon. In fact, if you read some of Cope's original descriptions, you find that the only feature he thought separated Naosaurus from Dimetrodon was the presence of transverse processes on the neural spines. Those are the little thorny side-projections present on the sides of the edaphosaur sail, contrary to the smooth, spike-like bony projections that make up that of dimetrodonts.

Cope thought that it was these side projections, which, while most were broken at the base, he estimated would could be up to half the length of the main neural spine in some specimens, that actually anchored the membranes of the sail! Cope pictured edaphosaurs with a series of membranous sails perpendicular to the torso, not parallel to it, similar to the configuration of the rigging of a large sailing ship rather than a sloop. As Cope said,

"In a full-sized individual, the longest cross-arms, which are the lowest in position, have an expanse of two hundred and sixty millimeters, or ten and a quarter inches, while the spine has about the height of five hundred millimeters (19.75 inches), the body being 60 mm. long. The animal must have presented an extraordinary appearance. Perhaps the yard-arms were connected by membrane with the neural spine or mast, thus serving the animal as a sail, with which he navigated the waters of the Permian lakes." (Cope 1888, p. 294).

While many prehistoric animals are described as having sails, it's interesting to keep in mind that this term seems to first have come about based on a hypothesized structure that was very different from the comparatively "normal" dorsal fins and ridges we're used to seeing today. Cope himself seems to have given up on the idea by the time he was supervising Charles Knight in a restoration of Naosaurus,** which other than the Dimetrodon-like skull, appears relatively normal by modern standards. Still, a proper reconstruction of a truly mast-sailed edaphosaur would be a nice challenge for paleoartists...

*Interestingly, most phylogenetic analyses nowadays suggest that these two types of sail-backed synapsids do not form a natural group with each other. So either the sails evolved convergently, or they are a trait of the common ancestor of the two types of animal. Which would mean our own ancestors were sail-backs!
**Knight later revised his Naosaurus painting, removing the transverse processes altogether and giving it an actual Dimetrodon skull, modifying it into simply a restoration of a Dimetrodon.

* Cope, E. D. (1888). Systematic Catalogue of the Species of Vertebrata Found in the Beds of the Permian Epoch in North America with Notes and DescriptionsTransactions of the American Philosophical Society16(2), 285-297.
* Osborn, H. F. (1897). A Great NaturalistCentury Magazine, November.

Sunday, September 1, 2013

You're Doing It Wrong : Dino Foot Scales

Above: Our subject matter.
It's often said by those who support a strict phylogenetics-based system of naming life that it's only by restricting well-known names from neontology (the study of modern organisms) to crown groups can we avoid making unjustified assumptions about members of stem-groups.

These kinds of unjustified assumptions have been rampant in the history of studying stem-birds. Archaeopteryx has traditionally been depicted, incorrectly, with a reversed hallux, and occasionally even with beak-like structures, simply because it's a "bird", and those are features all birds have. Except Archaeopteryx is not a true "bird", it's a stem-bird, more closely related to birds than to any other living animal group, but not a member of the group that includes all modern birds. It's fair to assume that an extinct member of the duck lineage, like Vegavis, had a bill, but that's not necessarily so for, say, Patagopteryx, despite the fact that it is usually referred to as a "bird".

Modern bird feet, by Philip Henry Gosse, 1849, public domain. Note overlapping scutes on
the top surfaces, and pebbly, polygonal reticulae on the bottom surfaces.

Most paleoartists have absorbed these kinds of warnings, and do a good job of avoiding obvious errors based on typology, the assumption that all species in a certain "type" share "key characteristics." But there are some typological memes in the bird lineage that are more pernicious, possibly because their actual evolution is something most artists don't think about very much.

Take, for example, the bird-like scutes that are almost universally illustrated covering the tarsus (upper foot/lower hind limb) of dinosaurs. Is there any evidence that these were actually present in any given group of non-theropod stem birds? Well... no. Not that I'm aware of (if you know differently, please comment!).

Sinosauropteryx prima with tarsal scutes.
Image by Matt Martyniuk,  licensed.
I'm not sure when this meme began, and if it's related to the Dinosaur Renaissance when the link between birds and dinosaurs was re-established. Looking at some Charles Knight paintings, such as his famous "Leaping Lealaps", it appears that the feet of his theropods were scaled based on modern lizards (more on the differences between lizard scales and other types of "scales" below). Bakker's influential early restoration of Deinonychus does not include any obvious scutes on the feet or tarsus. Mark Hallet, on the other hand, did include what look like oblong bird-like scutes on his theropods. At any rate, it's hard to deny that "bird feet" are typical of almost all modern reconstructions of dinosaurs, including my own, and are not limited to theropods. Bird-feet are often restored on ornithischians and even pterosaurs.

Of course, like many paleo-memes that developed during the 1980s, the main idea seems to be using this as a flourish to make otherwise scaly dinosaurs seem more bird-like. And thanks to skin impressions, we know that many dinosaurs had scales, right?