Ben Shoemate's Notebook

Prepare to have your mind blown.

Certain dinosaurs—physically disparate enough that we've always thought of them as different species—may actually be the same animal at different stages of its life cycle. Also: Those big, protective-looking bone formations surrounding some dinos' heads and necks probably weren't all that useful as a defense against predators.

Case in point, triceratops. Or, maybe we should be calling it torosaurus now, I'm not sure. See, according to research done by scientists at Montana's Museum of the Rockies, the familiar triceratops is really just the juvenile form of the more-elaborately be-frilled and be-horned torosaurus.

This extreme shape-shifting was possible because the bone tissue in the frill and horns stayed immature, spongy and riddled with blood vessels, never fully hardening into solid bone as happens in most animals during early adulthood. The only modern animal known to do anything similar is the cassowary, descended from the dinosaurs, which develops a large spongy crest when its skull is about 80 per cent fully grown.

Scannella and Horner examined 29 triceratops skulls and nine torosaurus skulls, mostly from the late-Cretaceous Hell Creek formation in Montana. The triceratops skulls were between 0.5 and 2 metres long. By counting growth lines in the bones, not unlike tree rings, they have shown clearly that the skulls come from animals of different ages, from juveniles to young adults. Torosaurus fossils are much rarer, 2 to 3 metres long and, crucially, only adult specimens have ever been found. The duo say there is a clear transition from triceratops into torosaurus as the animals grow older. For example, the oldest specimens of triceratops show a marked thinning of the bone where torosaurus has holes, suggesting they are in the process of becoming fenestrated.

There are other species this might apply to, as well. Some with even bigger shifts in appearance.

While this is a Big Hairy Deal for dinosaur science, it also elicits a little bit of a "duh" moment when you go back and look at the animals in question. What you should really be getting out of this story is an illustration of how difficult it is to study a creature that's been extinct for millions of years.

After all—as my husband pointed out—nobody would be shocked to learn that a baby chick, an adult chicken, and plate of parmigiana were all the same animal. But that's because we've experienced chickens. Were an alien to drop in on Earth for one afternoon, they might be just as amazed at the life cycle of poultry as we are now at the triceratops/torosaurus'. Paleontologists are tasked with reconstructing the lives of animals nobody has ever seen alive. And that creates a world where the obvious just isn't.

New Scientist: Morph-o-saurs: How shape-shifting dinosaurs deceived us

(Via John Taylor Williams)

One topic which generated a lot of discussion at the Gravity and Cosmology meeting was the void model of the Universe. The basic argument is simple: the dark energy is an ugly addition to our cosmological standard model, with 70% of the energy density of the Universe some mysterious substance with weird properties. From a theoretical perspective, dark energy has the wrong density by many, many orders of magnitude, and worse, we may never be able to study it directly in the laboratory. Now suppose I told you I had a model which explained all of the observations, was based on general relativity, and appealed to no mysterious dark energy component (but still has dark matter, unfortunately). Sounds tempting, right? This is precisely what John Moffat, Chris Clarkson, Antonio Enea Romano, Chul-Moon Yoo, and others were advocating at the workshop (Kenji Tomita has also done a lot of work on this; the model has been around for decades). There’s one important caveat, however. The void model throws out the homogeneity and isotropy assumption. The Universe is now spherically symmetric, with a big hole in the middle. Even worse, we happen to be very, very close to the center of the hole.

As I discussed in a previous post, John Moffat argues that we shouldn’t be any more disturbed by this model than the standard model, because they’re both anti-Copernican: the void model in space, the standard model in time. As I discuss in that post, I’m not sure I completely agree with this. The fine tuning for the average void model is fairly involved. First, the matter density must be carefully set, as a function of radius, to agree with observation of the luminosity-distance relation. Then we have to be set down within roughly 1 Mpc of the center of the spherical void (which is at least a few Gpc on a side). If we were at a random spot in the Universe, there’s a probability of much less than 1 in 10 billion that we’d end up sufficiently close to the center of a void (assuming such voids existed). On the other hand, the standard Lambda CDM model of cosmology requires fine-tuning of the cosmological constant to a tiny, but non-zero number. To some this is unbearably ugly. But, at the end of the day, it’s just one additional, arbitrary number.

All this being said, what’s great about void models is that they aren’t just a philosophical alternative to the standard model. This is physics. There are measurements that can be done to differentiate (and possibly falsify) these models. Stebbins & Caldwell have come up with one particularly interesting approach, exploiting the fact that “random” observers in a void model see a different sky (and hence, a different CMB) from the one we do in our privileged position. It is surprising that a model so radically different from our standard model is still viable (although under pressure). Tests over the next few years are expected to distinguish these models, and we’ll know definitively whether we are at the center of the Universe.