Disappearing Dinosaurs

Ok, so I know this is all a bit old news, but I have been away for an absolute age, and reading that your favourite dinosaur no longer exists instilled a kind of hurt inside me that is hard to shake.

I am, of course, talking about this (reasonably recent) study that reported that Triceratops was actually the juvenile form of Torosaurus, and which the media so gleefully interpreted as: “TRICERATOPS NEVER EXISTED!”.

I was saddened twofold.  Firstly I was saddened by the headline.  Is it true?  Could it be possible? Could those inimitable vertebrate palaeontologists, our standard bearers as the only kind of palaeontologist anyone has ever heard of, have got it wrong for all those years?  Are all those rickety wooden slot-together Trike models, and even my fabulous new rubbery reconstruction just a mockery of a ‘saur that never was?

And then I read the article.  I was saddened then, in a cynical, tired kind of way, by journalism.  I’m not going to get on my soapbox now, because this is about Triceratops (and later, Pachycephalosaurus), and I don’t want to steal their thunder.  But I was unsurprisedly disappointed by the misleading oversimplication or, if you want to be pessimistic, gross miserpresentation of the fact that Triceratops has some parents.

For anyone who has been living in a cave (presumably without Triceratops/Torosaurus fossils), or hasn’t the energy to read the original article, I will mention it briefly.  Triceratops was first described from a pair of brow horns from Colorado in 1887.  It is perhaps the most famous member of the Ceratopsidae, or horned dinosaurs, which also include the Styracosaurus with its extra spiky frill, and the Pachyrhinosaurus looking like it lost, badly, in a bar fight.  The new study, by John Scannella and Jack Horner, published in the Journal of Palaeontology on the 14th July, reports a hitherto unrecognised  relationship between Triceratops, and another Ceratopsid, Torosaurus.  Torosaurus was first named in 1891, and differs from trike in having a much larger frill with two holes through it.  It was previously thought to be a completely difference species of dinosaur but now, after comparitive anatomical study, it is likely that Torosaurus is the more mature form of Triceratops.  All trikes are, at most, sulky teenagers.  How is this possible?  Well, it is a pretty funky party trick of some of these dinosaurs that they can grow and reabsorb bone as they mature.  So trike’s growth spurt was not upwards or outwards, but frill-wards!

Reconstructions of the now synonomised Torosaurus, and Triceratops.

Alright, so I can sort of see where our eager journalists are getting the idea that Triceratops never existed.  If trike is only the juvenile form, then surely Torosaurus, our ‘grown-up’ should really take centre stage.  It is a very human viewpoint.  After all, if we were to choose a typical individual to represent the human race as a whole, morphologically speaking, we are unlikely to choose an ungainly, disproportioned toddler (I’m not just being mean about babies here – they really do have odd proportions.  All head and eyes and…).  Anyway, while the trashing of Triceratops might seem logical and curiously headline grabbing to most people, sadly it isn’t the scientific way of going about it.  Indeed, if any dinosaur never existed, it should be Torosaurus.  Bulky, mature, and probably very sensible Torosaurus had the misfortune of being described a whole two years later than Triceratops, and so in the eyes of science, the name is redundant now granddad has been proved to be the same as paradoxically older, younger Trike.  It is a pretty standard pop in taxonomy – combining synonyms (different names for the same beasties), you always keep the name that was coined first.  Poor Torosaurus.  Somehow “TOROSAURUS NEVER EXISTED!”  doesn’t have the same ring to it, seeing as most people have never even heard of the poor chap.  But if you ask me, I don’t know why we have to make a big deal out of trashing either of them.  True, the loss of a famous dinosaur is headline worthy, but is it not equally as headline worthy that these things REABSORB BONE?!  No? Thats just me then…

Changes in morphology as creatures grow up are not a rare thing, but do pose an extra problem to palaeontologists.  When we look at a fossil, be it a skeleton, or in even in my own case, a tiny microbial cell, it has been ravaged by time and the somewhat tedious chore of being buried under tonnes of rock for millions of years.  It is tricky enough to tell what it originally was, let alone who it might have been related to.  The study of ontogenetic changes in fossil organisms is a complex and varied field.  The ability of certain dinosaurs to grow bone on a whim, and then change it as easily as washing off a transfer tattoo, makes life particularly tricky for the palaeontologists charged with working out the family tree, as well as the evolutionary one.  Triceratops and Torosaurus are not the first dinosaurs lumped together as a happy family – as luck would have it, my very close second favourite dinosaur Pachycephalosaurus has also acquired some juvenile forms, once thought to be independent species.  The rather magnificently named Dracorex hogwartsia and Stygimoloch spinifer were proposed in 2007 by Jack Horner (of Triceratops trashing fame) to be juvenile forms of the more famous Pachycephalosaurus.  Dracorex has an incredibly rough and spiky skull, with no sign of the characteristic bony dome.  The adolescent Stygimoloch has started to grow a small dome, at the sacrifice of some of its spikes, which are reabsorbed.  The fully mature Pachycephalosaur has lost the majority of its spikes, limiting it to a collection of rather stumpy cones around the large bony dome that makes it so famous.

Skulls of related pachycephalosaurs: Dracorex hogwartsia, Stygimoloch spinifer and Pachycephalosaurus wyomingensis

So far from a tragic loss to science of some of its flagship dinosaurs, the super work they are doing at Montana State University and elsewhere, to make ontogenetic links between weird looking creatures, is more than just good science.  It is a fascinating insight into just what our extinct cousins were capable of.  I can’t help but think that all this bone growing and reabsorbing must have contributed to some substantial growing pains, and the Cretaceous was really just full of angsty grumpy teeanage ‘saurs.  Not so far removed from most colleges today!

Relevant Papers

  1. Scannella and Horner (2010) – Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): Synonymy Through Ontogeny. Journal of Vertebrate Palaeontology, 30, 1157-1168.
  2. Erik Stokstad (2007) – Society of Vertebrate Palaeontology Meeting: Did Horny Young Dinosaurs Cause Illusion of Separate Species? Science, 318, 1236

All images herein are original and © Leila Battison 2010.  High resolution versions of the individual illustrations can be found in Illustration

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