Thursday, 17 January 2013

The Feathered Elite



A recent post from the guys over at Love in the Time of Chasmosaurs brought to our attention the palaeoimagery of Alexander Lovegrove whose many fine works can be seen over at deviantART. Alex is obviously a big fan of tyrannosaurs and he depicts many taxa in various artistic situations. In the LITC post one image, in particular, caught my attention and that was the one above and featuring my beloved Daspletosaurus attacking a herd of chasmosaurs. Please note that the image is used with the artist’s permission.

The daspletosaur is depicted with a light covering of fuzz along the upper portion of the body running from the lacrimal horns to the tip of the tail. What makes this image stand out are the naked legs which Alex points out were influenced by an article by Andrea Cau who suggested that it was possible that large theropod dinosaurs that were fully covered in integument would probably be able to avoid substantial overheating issues.

Ostriches display bare legs such as these and, when the wing feathers are raised exposing the thigh, help with dissipating excess heat. Whether or not you want to subscribe to a hypothesis like this for dinosaurs, I liked the idea of Alex’s “chicken drum-stick” legs and this got me thinking about feathers and fuzz and what they would mean to theropods and particularly to tyrannosaurids proper as opposed to tyrannosauroids in general.   
  
So if we avoid the many heated discussions regarding feathers in theropods such as maniraptorans and whether they flew or climbed and, indeed, the origin of flight completely – then we have quite an interesting topic ahead of us. The fact that Yutyrannus has finally condemned the notion that big theropods could not have a feathery covering of some description makes for interesting speculation.

So how would big theropods have utilised a fuzzy or feathery covering? Well we can eradicate one notion straight away and that is that these animals flew – remember we are only dealing with large theropods here. When you think about it, even the smallest of theropods would have struggled to fly since they were not that advanced aerodynamically anyway.

Using fuzz or feathers as form of temperature control is another matter completely and there is enough information out there to fill an entire database. It would seem unlikely that whatever shape or form the integument took that it would not have been used in this way in some form or another. We are all aware of dinosaurs that lived in the Polar Regions and it would seem a reasonable assumption that even large theropods would have benefitted from a covering of feathers or similar to help them keep warm.

Downy feathers today help birds incubate their eggs and we all know that some smaller dinosaurs certainly incubated their eggs so it is possible that animals such as oviraptorosaurs and perhaps dromaeosaurids also had a downy insulation for this purpose. Perhaps it may have been a seasonal development – growing only for the nesting season before being moulted shortly afterwards. It would also seem reasonable to assume that feathers and fuzz would have been utilised as nesting material as well to help line a nest. Pure speculation on my part, of course, but it does seem a reasonable hypothesis. Of course, when you get to large theropods, then incubating eggs becomes somewhat difficult, probably impossible – especially when you weigh upwards of a couple of tons.

The biggest single use of feathers and fuzz in, not only theropods, but dinosaurs as a whole would be for intraspecific communication and signalling. This is undoubtedly the most important function for feathers within today’s extant bird populations and, by implication, must have been just as important to non- avian dinosaurs. Species recognition, courtship and intimidation are just a few of the distinct uses that large theropods would have utilised if they had displayed a feathery covering.



It seems likely that colour would have played a part as well since most dinosaurs likely had good colour vision. It’s interesting to think that some theropods may have become distinctly brightly coloured during courtship and rutting periods (did dinosaurs “rut”?) and the lacrimal horns of theropods are often portrayed as brilliantly coloured in restorations and, in tandem with a distinct plumage, could have made for a wondrous display.

Not that I am in favour of many of these gaudy technicoloured restorations that we see today – far from it. Of course, it is possible that many species may have been brightly coloured but I am just not buying it – it makes no sense. If I was a big 30 foot theropod on the lookout for prey then the last thing I would want to do is advertise my presence by strutting around in a gaudy multi-coloured plumage. No – I believe that that colours utilised would have been used much more subtly - only being brightened up during the aforementioned breeding season.

This brings us nicely to another possible use for integument – camouflage. For me this makes much more sense and the adaptability of feathers and fuzz to take on the colours of their surroundings would make for a stealthy and very effective predator. Herbivorous dinosaurs could have been as equally adapted. I am a big proponent of this anyway since fully scaled dinosaurs could have easily utilised the same technology lest we forget that both fuzz and feathers are derived scales. 
    
One use of feathers that is not often appreciated in extant birds is their ability to produce sound. Scientists are only now really coming to grips with this aspect of a bird’s communication and there are not that many documented cases. Birds such as Wilson’s`snipe, grouse, peacock and manakins all make sound with specialist feathers and one, the club-winged manakin, actually rubs feathers together almost like a violin to produce sounds to entice a mate. However, I do not believe that feathered theropods would have had feathers derived enough to make such sounds or, indeed, the dexterity to perform such an act – but it is an interesting concept.

Keeping with sound – is it possible that any theropods used facial fuzz or feathers to channel sound into their ears? The most obvious example of this today is the owl which surrounds its huge eyes with two almost circular depressions constructed by feathers which function like satellite dishes to collect sound and this enables the owl to hunt with astounding accuracy even in the blackest of nights. Whilst I do not believe that any large theropod evolved similar evolutionary traits I suggest that we do not completely dismiss this notion.

Certainly the small theropod Troodon formosus had large eye sockets which lead some palaeontologists to suggest it was nocturnal. It may have also displayed specialist feathers to help channel sound at night. Similarly the small ornithopod Leaellynasaura also had large eyes and endured long periods of perpetual dark in the Polar winter. It would seem very reasonable to consider that any feathered nocturnal dinosaur would evolve their feathers in whatever way was necessary to survive.  

Of course, something I have mentioned in previous posts is that if large theropods had a fuzzy or feathery covering then it would need to be kept in pretty good condition through regular maintenance and grooming otherwise it would soon be of little use. Birds do this today by preening and having both dust and water baths and it is an interesting scenario imagining a big tyrannosaurid trying to preen or rolling around on the ground for a dust bath. This is one of the things that has always caused me to doubt whether big tyrannosaurs were feathered – could an adult T.rex weighing anything from 5 to 7 tons have the dexterity to preen? Would it really have rolled on the ground for a dust bath? In my mind the answer is no but I am not daft enough to deny that it was possible. Only time will tell on this one.

Black Heron - image courtesy of Wikipedia


One final use of feathers as a hunting aid may seem a bit fanciful but, again, perhaps we should not completely dismiss the notion. The black heron uses a technique known as canopy feeding whereby it uses its wings to form an umbrella which in turn attracts fish under the canopy enabling the heron to strike at the fish. Can you imagine the giant fish eating theropod Spinosaurus fishing this way? What a sight that would have been!

So how would I perceive what a feathered tyrannosaurid may have looked like? I think most interpretations of the head have been reasonable and are very similar to Alex’s Daspletosaurus although I believe that even this might be slightly overdone. A big tyrannosaur with a fresh kill would likely go for the tasty innards first and opening up the torso of a big hadrosaur or ceratopsian would enable the predator to bury his head into the body cavity to remove the offal.

Vultures do this today and their entire head and neck are virtually feather free. This makes a lot of sense to me since congealed blood and other body fluids would soon make a mess of feathers and fuzz. So I would expect a tyrannosaurid to have a pretty bare head although I do not discount a few token feathers developing during courtship.

The small arms of tyrannosaurids continue to spark debate about whether they had some use or, indeed, were vestigial.  I believe that they did have a use and I currently hypothesise that they may have been used for courtship and/or the act of mating. It is entirely possible that these forelimbs may have been feathered and used for display or to send courtship signals. This may take a leap of faith in some circles but extant large animals often display surprising delicacy when it comes to mating and since tyrannosaurs were probably sexually dimorphic then it makes sense to have some form of technique, when approaching a larger prospective mate, that your intentions are honourable!

I would also tend to agree that the legs in tyrannosaurids would remain unfeathered although this is much harder to quantify. Certainly, at lower levels, it would make sense to keep the legs free of integument and then they would not catch on bushes and plants or impede the carnivores’ progress during a hunt.
As for the rest of the body and tail I like Alex’s interpretation of Daspletosaurus which displays a half-and-half coverage. This would seem to have a lot going for it in as much that there is enough bare skin to help control the body temperature should the animal get too hot whilst the upper coverage affords protection from the elements as well as help retaining body heat.

So all in all it would appear that there are significant advantages for a tyrannosaurid having some form of integument whether it is feathers, fuzz or a combination of both. But as is my way I remind you that Tyrannosauridae is still feather free for now but I now find myself actually looking forward to the day that a tyrannosaurid is found with feather impressions and if not – well that just means my scaly clade remains just as awesome as it ever did. Long live the Kings!

This has been doing the rounds on the social networks - made me laugh anyway!


3 comments:

Anonymous said...

"One final use of feathers as a hunting aid may seem a bit fanciful but, again, perhaps we should not completely dismiss the notion."

I'm surprised you didn't mention Fowler et al.'s RPR hypothesis.

"The black heron uses a technique known as canopy feeding whereby it uses its wings to form an umbrella which in turn attracts fish under the canopy enabling the heron to strike at the fish."

Makes me wonder if any unenlagiines used their wings in the same thing.

"Can you imagine the giant fish eating theropod Spinosaurus fishing this way? What a sight that would have been!"

Have you seen "Monsters Resurrected - Biggest Killer Dino" ( http://www.youtube.com/watch?v=fWe_pz_cv3g )? I ask b/c, in said doc, it's speculated that Spinosaurus used its sail in the same way.

-HD

Mark Wildman said...

We really need a complete vertebral column of Spinosaurus - or as near as complete as makes no difference. This would certainly help to ascertain the use of the sail but I am not convinced that it would be used as an aid to fish.

When you consider that Ouranosaurus was also sail backed and a contemporary of Spinosaurus, this then suggests to me that something else was going on here but I regret that I do not know the answer!

Anonymous said...

Don't get me wrong as I wasn't agreeing w/the speculation, just saying that it was speculated. Bakker put it best when he said, "Things that stick out of your head or stick out of your back are nearly always used first to intimidate...sexual rivals" ( http://www.youtube.com/watch?v=bptxfX9KNas ).

-HD

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