Morph-osaurs: How shape-shifting dinosaurs deceived us
Morph-osaurs: How mould-shifting dinosaurs deceived us
28 July 2010 by Graham Lawton
Magazine exit 2771. Subscribe and save
For similar stories, visit the Dinosaurs Topic Guide
Read replete article
Continue reading page |1 |2
DINOSAURS were guise-shifters. Their skulls underwent extreme changes throughout their lives, growing larger, sprouting horns at that time reabsorbing them, and changing shape so radically that different stages mien to us like different species.
This discovery comes from a study of the iconic dinosaur triceratops and its obstruct relative torosaurus. Their skulls are markedly different but are actually from the actual same species, argue John Scannella and Jack Horner at the Museum of the Rockies in Bozeman, Montana.
Triceratops had three facial horns and a pointed, thick neck-frill with a saw-toothed edge. Torosaurus also had three horns, granting at different angles, and a much longer, thinner, smooth-edged decorate with ~s with two large holes in it. So it's not marvellous that Othniel Marsh, who discovered both in the late 1800s, considered them to have existence separate species.
Now Scannella and Horner say that triceratops is absolutely the juvenile form of torosaurus. As the animal aged, its horns changed frame and orientation and its frill became longer, thinner and less indented. Finally it became fenestrated, producing the classic torosaurus form (see diagram, right).
This extreme shape-shifting was possible because the bone conglomeration in the frill and horns stayed immature, spongy and riddled by blood vessels, never fully hardening into solid bone as happens in principally animals during early adulthood. The only modern animal known to vouchsafe anything similar is the cassowary, descended from the dinosaurs, which develops a extensive spongy crest when its skull is about 80 per cent full grown.
Shape-shifting continued throughout these dinosaurs' lives, Scannella says. "Even in the greatest part mature specimens that we've examined, there is evidence that the brain was still undergoing dramatic changes at the time of death."
Even in the ~ numerous mature skulls, there is evidence that they were undergoing dramatic changes
Scannella and Horner examined 29 triceratops skulls and nine torosaurus skulls, for the most part 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 diverse tree rings, they have shown clearly that the skulls come from animals of unlike ages, from juveniles to young adults. Torosaurus fossils are much rarer, 2 to 3 metres to a great extent and, crucially, only adult specimens have ever been found.
The duo declaration there is a clear transition from triceratops into torosaurus as the animals grow older. For example, the oldest specimens of triceratops show a eminent thinning of the bone where torosaurus has holes, suggesting they are in the series of measures of becoming fenestrated (Journal of Vertebrate Paleontology, vol 30, p 1157).
The finding has implications for the supposed defensive function of the triceratops' gathering. "If I was a triceratops I wouldn't want anything also damaging to happen to my frill, as it had numerous broad blood vessels running over the surface," says Scannella. "I don't imagine holding up a emaciated bony shield that can gush blood would be a very potent means of defence."
Instead it is likely that the headgear was a display to signal an individual's maturity to other members of the shape. Differences between the sexes is another possibility but less likely, says Scannella.
It was even now known that triceratops skulls changed throughout their development, but not that the last result was a torosaurus. Torosaurus will now be abolished as a description and specimens reassigned to Triceratops, says Horner.
Triceratops isn't the singly shape-shifter. Last year, Horner and Mark Goodwin of the University of California, Berkeley, claimed a part similar for another iconic Hell Creek dinosaur, the dome-headed pachycephalosaurus, by chance best known for headbutting jeeps in Jurassic Park 2.
Two resembling dinosaurs, classified as Dracorex and Stygimoloch, are also known from Hell Creek. Horner and Goodwin affirm that they are not separate species but juveniles of pachycephalosaurus (PLoS One, vol 4, p e7676). If with equal rea~n, this is an even more extreme case of shape-shifting than triceratops, with the animal growing horns and then re-absorbing them into its brain as it ages (see diagram).
Soft in the head
Horner says this makes it unpromising that pachycephalosaurus engaged in headbutting as it, too, retained spongy, rudimental bone throughout adulthood. As with the frill of triceratops, its cathedral was probably used for display.
On top of that, a dinosaur called Nanotyrannus has been tentatively reclassified for the re~on that a juvenile form of Tyrannosaurus rex.
Taken together, the "loss" of four group from the Hell Creek formation reveals that the dinosaurs that lived in that place up until 65 million years ago were not as diverse similar to previously thought. Triceratops and torosaurus have long been regarded as the continue survivors of the horned dinosaurs, a large group that appeared in the Jurassic and reached its exultation about 80 million years ago. Now it seems that only single in kind species made it through to the end of the Cretaceous. This could have existence evidence to support a disputed theory that dinosaur diversity was in marasmus long before an asteroid impact wiped them out.
Both Scannella and Horner recite it is possible that other dinosaur species from Hell Creek power of choosing turn out to be juvenile forms, and add that the like thing is probably true of dinosaurs from other locations and epochs. "Juvenile dinosaurs were not just miniature versions of adults - they looked extremely different and could easily be mistaken for distinct species," says Scannella.
Read abounding article
Continue reading page |1 |2
New Scientist
Not correct a website!
Subscribe to New Scientist and get:
New Scientist warehouse delivered to your door
Unlimited online access to articles from through 500 back issues
Subscribe Now and Save