Tarbosaurus is best known for being a close relative of Tyrannosaurus rex, but what is not so well known is that it is possible that it had a wattle! Or at least something very much like it. I couldn't find the original paper on the discovery, but there have been several mentions on various sources about the wattle.
Before we go into all that, first let's take a quick look at the genus.
A skeletal reconstruction of Tarbosaurus
Tarbosaurus grew up to 12 metres long (39 feet), and was nearly or just about comparable in size to its close relative, Tyrannosaurus. Its skull was more than 1.3 metres long (4.3 feet), and from fossil evidence, we know that it was adapted for withstanding great stress as it bit down. It lived around 70 million year ago, during the Late Cretaceous, and was found primarily in Mongolia. At the time, this area was a tropical, humid floodplain.
Now down to the interesting bit. There has been one case of a preserved structure on the dinosaur's chin that looks like a wattle.
This diagram shows where a wattle is and what it looks like. Tarbosaurus possibly had a similar wattle to this turkey.
Why would a 13 metre long predator need a wattle? Well, it could have been for several reasons.
Reason 1: Attracting a Mate
If we look at modern day birds, why do they have wattles? This is obviously excluding those which have been selectively bred to have a large wattle.
For the most part, modern birds use their wattles to impress a mate. The larger the wattle, the healthier it is and the higher its testosterone levels, indicating to the female how healthy he is.
It is possible that Tarbosaurus also used its wattle during a courtship ritual - possibly expanding it, or filling it with blood to make it go bright red.
Reason 2: Temperature Regulation
Chickens use their wattles to cool themselves down. They are filled with blood vessels, so as the blood is pumped into the wattle, it is cooled close to the skin, then pumped back into the body, now cooler. In its tropical, hot envioroment, it is possible that Tarbosaurus used a similar system. Edit: though obviously since it has a much larger body than a chicken, the system would not be so efficient and easy. However, maybe it could have been expanded when it needed to cool down, to increase the surface area? Of course, looking at elephants and the size of their ears (Asian elephants probably being a better comparison than African elephants, given the habitats), which they do use for cooling purposes, it does not seem so unlikely that Tarbosaurus did a similar thing.
But perhaps it wasn't a wattle at all, but instead a throat pouch, akin to that of a pelican?
A pelican displays its throat pouch- is it possible that Tarbosaurus had something similar?
The thought is an intruiging one, but to be honest, I am doubtful. Let's take a look at the reasons.
1: Catching Prey
Pelicans dip their heads into the water, scooping fish up in their pouch - but this method of food capture wouldn't be possible for the terrestrial Tarbosaurus, which most likely ate large animals like sauropods. It certainly wouldn't be scooping one of those up in a throat pouch!
2: Food Storage
However, maybe Tarbosaurus stored chunks of meat in its throat pouch for later. In the tropical climate and the dampness of the throat pouch, the meat would quickly fester, though - so if it did have a throat pouch and it used it for food storage, it wouldn't be able to keep food in there for very long. Besides, why would it need to store food for later? It's the dominant predator, it can just hang around and guard its meal until it's ready to eat again.
I think that Tarbosaurus had a wattle, not a throat pouch, and that it was brightly coloured, used for attracting a mate, as it is the most obvious reason. Its wattle was probably most obvious in adult males. Maybe it could be expanded to impress a potential mate, the size of the wattle showing the male's strength? And perhaps it was full of blood vessels, making the wattle a sort of self-cooling device too, though how efficient this would be with such a large animal compared to a small wattle, is debatable.
As a speculative touch, perhaps Tarbosaurus's face was colourfully carunculated and covered in fleshy folds, like the turkey? This would be another aspect to impress a mate - the size and vibrancy of the colour would indicate health. Also, if we look at modern-day birds which engage in face-biting behaviours, many of them have similarly carunculated faces. This is, as Duane Nash explains on his blog Antediluvian Salad, to protect its face and eyes. To quote him:
"What I am saying is that the convergence of a heavily adorned, wattled, dewlapped, caruncled, and combed cervical adornment in these three highly combative modern aves should not be glossed over. Usually interpreted as sexo-social signaling devices - and I am not disputing this adaptation - I think that they offer another, more functional usage. That is that in combat they offer up a convenient - and brightly colored - choice target to get bit upon. Why would a combative animal have such evolutionary pressure to offer up a choice morsel to get bit upon? Because losing a chunk of skin is preferable to losing an eyeball!! Feathers would be less than ideal because once plucked out little defense is left."
I strongly agree with him on this notion. And, to get to the meat of the story, theropod dinosaurs fought, and we know that they attacked each other's heads from the scars left on the skulls. They definitely would have benefitted from the carunculations Duane describes.
Therefore, maybe Tarbosaurus not only had a wattle, but a carunculated, warty face. If all of this was the case, then I would say that the wattle would probably be red - due to the large amount of blood vessels there, and also because it seems to be a fairly attractive colour to female birds, so perhaps it was the same for dinosaurs. I would have thought that the carunculated face was either the same colour, or a contrasting colour such as blue, or both. Red seems to be a dominant colour amongst carunculations on face-biting birds, drawing the enemy's attention to the skin instead of more vulnerable areas. It seems likely that if Tarbosaurus did have such carunculations, it had a similar colouration.
To finish off, I drew how I imagine Tarbosaurus could have looked:
The individual I have drawn here is a male, which is why it looks so flamboyant. His wattle is swollen and red, and his carunculated face is also red, although there is blue around his nose and lips. I am as to yet uncertain whether I agree on the 'theropods-had-lips' theory - I need to do more research before I will decide - but I decided to depict my Tarbosaurus with lips hiding his teeth. In some areas, his fat, carunculated lips hang down in lumps. I also drew a few bristle-like proto-feathers on his neck and sprinked over his eyebrows, nose, chin, and wattle.
Of course, I - nor anybody else - can be certain on this. Unfortunately soft tissue such as wattles are extremely rarely preserved - so turkey-Tarbosaurus could have been strutting around Mongolia, and we'll never find any more evidence of it. However, I really hope that we find more evidence of wattles, but even if we don't, it's good fun to speculate.
So, there's my theory on Tarbosaurus. That's all for now, and I hope that you enjoyed.