26 August 2010
Posted in DinoDigs
Most folks rarely give much of a thought to Torosaurus, except for the trivia answers to “Which animal has the longest skull of any land creature, ever?” But some people seem to feel inexplicably attached to this name, often and incorrectly translated as "bull lizard" (it's got big horns, and was ornery like a raging bull!). In reality it means "perforated lizard", in reference to the holes in its frill. These innocuously incomplete frill holes are at the center of the newest paleocontroversy, which has some scientists ready to erase the name Torosaurus from the dictionary altogether!
See also: Obsolete.
We’ve known for a while that dinosaurs can dramatically change as they grow up. Infant sauropods pack on over 100 pounds a day on their lifelong journey to become the world’s largest land animals. The crested trombone skull of Parasaurolophus [PA-rah-SORE-oh-loaf-us] wouldn’t begin to grow until it reached maturity, with the males being larger for producing deeper resonating sounds and attracting mates.
Pictured at Left: The Barry White of the Cretaceous Period.
According to the study, the skull of Triceratops exhibits a number of skull traits shared by Torosaurus, including thin parietal [pa-RITE-al] bones and elongated squamosal [skwah-MOSE-al] bones. In addition, microscope examinations of thin slices of bone from Triceratops and Torosaurus specimens reveal that individuals attributed to Torosaurus are more mature than any of the ones assigned to Triceratops. But the finding raises the question of why fossil hunters have recovered so few of the mature Torosaurus specimens-fewer than a dozen, compared to the many dozens of younger Triceratops.
There will be a test.
Compare the two skulls against each other again. In this image, we see the skull of Torosaurus latus next to the skull of our female Triceratops horridus (It's the full skeleton labeled “prorsus” in DinoDigs right now.) Distinct differences are visible between both skulls – the lack of serrated bumps around the frill, and the forward-curving cheek bones (called jugals) . There are also differences in the shape and curvature of the horns. The hypothesis put forth by Horner and the others claims that as the dinosaurs moved past the reproductive stage of life they no longer needed to fight for mates or defend the herd. Their skulls would reform, changing shape dramatically, leaving two large fenestra [FEN-ess-trah] or simply, holes, in the dinosaur’s skull.
Round up the usual suspects.
The green silhouette is Torosaurus, the blue silhouette is Triceratops. The eyes are a good place to line up the skulls, since most animals’ eyes stay the same size throughout their lives. Are there any parts of the dinosaur’s skull which match? Are their any parts which don’t match?
What if they’re right?
If the hypothesis ultimately proves correct, then the official name “Triceratops horridus” will be applied to any dinosaur previously called “Torosaurus.” It might stick about as well as the “Apatosaurus / Brontosaurus” change, because nobody says “Brontosaurus” anymore.
Nope. Nobody at all.
This also would suggest that there is less dinosaur biodiversity than originally thought—if there were only a handful of 3-horned ceratopsians, then they must have served a much larger role in their ecology. Every living animal today serves some role in their ecosystem, whether they are predators, prey, or partners. All the major ecological roles have been almost continuously occupied since at least the Cambrian Explosion roughly 542 million years ago. Although animals are generally highly specialized to their ecological roles, some animals share roles, and some evolutionary lineages can evolve from one ecological role to another. Torosaurus it seems, had a role too similar to Triceratops to be its own animal.
What if they’re wrong?
If the hypothesis ultimately proves incorrect, then Torosaurus latus will continue to be its own animal, just one that looks very similar to Triceratops (whose name I'm just Copy+Pasting at this point...), and the dozens of other ceratopsian dinosaurs. Scientists will need to find some juvenile Torosaurus remains that can solve that problem for us. We've already found infant Triceratops remans that do not have the fenestra in their frills.
And they're adorable.
It also calls into question the last few years of work by Dr. Jack Horner, who led this team on its previous efforts to combine the species’ “Stygimoloch” & “Dracorex hogwartsi” into juvenile forms of Pachycephalosaurus. and then again to lump Nanotyrannus as a kid-sized Tyrannosaurus. Both efforts failed scientifically, but made headlines publicly.
He can't see you if you don't move.
Most paleontologists invest great amounts of time and energy in the important areas of their field—expanding the breadth of knowledge about prehistoric animals and making discoveries that advance our understanding, not revise it. If future paleontologists look back and say that there was only one type of Lion, and it includes Panthers, Tigers, and their juvenile form: the housecat, we'd take issue with it. So why should that logic apply to animals that don't exist anymore?