The Stiff-Tailed Dinosaur Syndrome

by Carlos Augusto Chamarelli

Hello everyone, PK here, which means it’s time for some good old paleoartistic criticism and bashing of current ideas! So enjoy today’s topic: dinosaurs tails.

As everyone knows, for the longest time since their formal description in the mid-19th century, dinosaurs were thought to be tail-draggers in the same fashion as reptiles, because reptiles are lazy and so should be dinosaurs since they were reptiles. Or so it seemed, as it was about in the 70’s when the “dinosaur renaissance” came into scene, replacing the slow-moving and swamp-dwelling giant lizards for active, warm-blooded animals.

And considering the topic, the most important of all these changes is that they now had their tails off the ground, but then things sort of went downhill from there: artists started to depict their dinosaurs with increasingly elevated tails, to the point where, in the last 10 years or so, dinosaurs are always pictured as having their tails completely parallel to the ground and almost pointing upwards!

I, for one, am convinced that this idea was something paleoartists – both amateur and professionals – simply misunderstood. Namely – while dinosaurs may very well been able to maintain their tails parallel to the ground, they may not have done so at all the time.

There’s one important factor about dinosaurs that I have the slight feeling some artists overhead, or just plain ignore for a more dramatic effect, is that dinosaurs are animals just like the ones that live today, and as such, dinosaurs most certainly would get very tired sometimes. See, there is not a single animal in the world that maintains any of its limbs in a certain position for too long, and dinosaurs would be no exception: maintaining their tails elevated in a horizontal posture for so long would be exhaustive.

In other words, dinosaurs were able maintain their tails above the ground, but just enough; namely, they had droopy tails for the most part.

I went to brainstorm with RSN about this possibility, and he reminded me of an important detail: some dinosaurs were found with fossilized tendons on their tails. So naturally I had to research about that and what it would mean for the droopy-tail idea. One such evidence is found in the first ever Corythosaurus remains discovered by Barnum Brown in 1912, which is nice because for me ornithopods are the worst offenders of the rigid-tail idea. Now, please, take a look at this picture:

Picture of a giant helmeted duck.

Corythosaurus casuarius skeleton, by Barnum Brown, 1916.

Not only the creature’s skeleton was found almost complete, skin impressions are also present, but take a closer look at the tail; specifically the base, right above the ischium. Those distinct line markings you see were made by tendons which, supposedly, helped the animal maintain his tail in the same horizontal position as seen in this skeleton. But where exactly does this leave the idea that dinosaurs had droopy tails then? Go ahead, I’ll give you a few seconds…

You see it yet? Ok, I’ll make it more clear with this other picture:

Corythosaurus

Drawing of the fossil, by Barnum Brown, 1916.

Yes, as you can see, those tendons were present mainly at the very base of the tail. Not only that, but consider the caudal vertebrae also have a slight irregular shape when lined horizontally, but not so much if you curve it downwards – this also happens in other dinosaurs such as sauropods. In other words, the tendons only helped the Corythosaurus to maintain the first half or so of its tail elevated.

From what could be inquired from mummified hadrosaurid findings, duck-billed dinosaurs (as they are informally called) had a longer digestive system than other plant-eating dinosaurs. The elevated tail base means there is some more free room for processing the plant matter. Maybe not for much, but it was a very welcome addition.

But naturally dinosaurs didn’t had tails to digest plants. Tails are primarily used for balance, and in some animals it can also serve as a weapon, other might use them to call attention of mates or signalizing for each other in a group. Some animals, however, have no need for any of these, so what usually happen is that the tails have so little impact on its lifestyle that they quickly degenerate, resulting in stumps or completely disappearing. Just like what happened to us humans.

But dinosaurs had big tails – except for those who became birds and other not-quite-bird-yet small theropods such as Epidexipteryx – it’s one of their trademarks that make them so different from any other large animal today. But not all dinosaurs used their tails for balancing.

Epidexipteryx hui skeleton, discovered in 2008. Notice the shortened tail, compensated by the elongated feathers. Photo from National Geographic.

For example, armored dinosaurs such as ankylosaurids, nodosaurids and stegosaurids. With a low profile and sturdy legs, having a tail for balance isn’t needed, but they still had well formed tails for a single reason: they were mortal weapons. Stegosaurids had piercing spikes, nodosaurids had rows of sharp blades and ankylosaurids had a mass of bone at the tip that formed a fearsome weapon against predators.

Tail club of Euoplocephalus tutus, an ankylosaurid. Photo by Ghedoghedo, from Wikipedia, 2011.

Sauropods, at least the ones without extreme long neck lenghts, wouldn’t need such a long tail for counterbalancing; their torso might have been enough. These would then be free to be used as weapons since they couldn’t back-off predators with sheer size alone, and surely enough, some sauropods such as Diplodocus had elongated tails that ended in thin bones that could be used as whips, and the chinese Shunosaurus had a bone club similar to that of ankylosaurids. Both dinosaurs, while much larger than any living terrestrial animal, are visibly rather small for sauropod standards.

Skeletal reconstruction of the Spinophorosaurus nigerensis from Africa, which closely resembles the chinese Shunosaurus both in size and weaponry. Souce: Remes K, Ortega F, Fierro I, Joger U, Kosma R, et al. (2009).

On the same note, brachiosaurids had huge front legs which supported an extreme neck, but their tails were very small compared to other sauropods. So small in fact, they couldn’t be used for anything and one wouldn’t be surprised if their tails became stumps had they survived long enough.

Brachiosaurus brancai (now Giraffatitan brancai). Picture by Paul Olsen, 1988.

Now there are the odd ones: Ceratopsians. The larger ceratopsian that dominated North America in the late Cretaceous period landscape are known for their huge frills and huge horns and sturdy bodies… and for having rather pathetic-looking tails. These were relatively short and thin, and it’s hard to imagine that ceratopsians used them for counterbalancing their skull – which is in some way confusing since they might have been quite heavy even with the “windows” on the frills to decrease the weight.

And even odder ones: Pachycephalosaurids. These dinosaurs are known for their thick skulls which they used for head-butting contests (yes), but they are also known for the woven net of tendons at the tip of their tails. The total opposite of what usually happens.

So where do ornithopods such as Corythosaurus fall in all of this? My guess is that they used them for balance, but only when running on their hind legs. See, duck-billed dinosaurs had very small arms compared to his legs, with hoof-like hands, which is good evidence that they could walk on four legs as well as two legs.

A grazing Corythosaurus did not need their tails to be parallel to the ground; their arms would enable them to stand with a droopy tail. But on the sign of danger, things change: unsuitable to handle the stress that running on all four would cause, they would stand on two legs and run; the tail tendons then would enable the animal lift his tail to counterbalance its body while running. In this respect, the dinosaur would then function more like a theropod rather than a ceratopsian, per se. When away from danger, the tendons relax and the animal tail goes back to its droopy position. Corythosaurus would then look something like this (thanks RSN for the picture!):

Corythosaurus in relaxed position (above) and running from danger (below). Picture by Rafael Silva do Nascimento, 2011.

So there you have it. Dinosaurs had many uses for their tails, and just because they had tendons and warm blood it doesn’t mean they had steel rod for tails. While Corythosaurus is used as a starting point for the idea, keep in mind other dinosaurs also could have droopy tail, including the ones that used their tails for balance such as theropods.

So if you ever see a picture of a dinosaur, any kind of dinosaur, standing still or having a nice stroll, and said dinosaur is doing it while having their tails completely parallel to the ground, you’re allowed to shout “WRONG!”, because that dinosaur must be tired as heck of having his tail like that.

Hope everyone enjoyed reading my article; if you have any questions just comment and I’ll answer it.

Thanks for reading!

– – –

References:

Leonardo, the mummified dinosaur. Available on-line in: <www.youtube.com/watch?v=ihifMrV3-pY>. Acess on December 1st, 2011.

Paul, G. S. et al. 2010: The Princeton Field Guide to Dinosaurs. Princeton University Press.

Wikipedia. Corythosaurus. Available on-line in: <en.wikipedia.org/wiki/Corythosaurus>. Acess on December 1st, 2011.

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Filed under Paleoart, Paleontology

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