STL Science Center

STL Science Center

13 July 2013

Rakes for Hands, Giant Heads

Cast in Brussels, photo by Ghedo
Some inconceivable reason caused the curators of the Museum of Natural History in Brussels to take a rather nice cast of the rhabdodontid dinosaur Zalmoxes and give it rakes for hands and feet. A great deal of the skeleton of this genus, spread over two Romanian species and, potentially, a third Austrian species, is well known, but this does not include fore and hind feet. Despite this, enough is known of the rhabdodontid iguanodonts that a reasonably educated guess could have been easily made for the casting of this skeleton. Regardless, we can get a sense of the overall dimensions and lay out of the skeleton of these species by looking at this cast. The scapulae are rather slender and long, which is pretty interesting and the skull is a triangle of sturdy thick bones with a fairly nice dental battery found inside the mouth. The skull truly sets Zalmoxes apart from many other dinosaurs and as such, we will definitely be looking at that in a moment.

Attributed to Anky-Man
The skull, if not the skeleton, of Zalmoxes, is quite robust. Muscles would have create a fairly good bite force, but in all likelihood the main manner of getting energy out of its food would have been through a lot of grinding of the dental battery. The mouth, and it is always up in the air when discussing this, may have been enclosed in a flap of cheek to help in chewing plant matter. A cheek is instrumental in holding vegetation in the mouth during mastication; without a cheek your food would mostly end up falling out onto your favorite t-shirt unless you held it in there with your hands. The skull of Zalmoxes is very iguanodontid in overall shape and form, but it is small and, given the size, more robust than seems necessary for this dinosaur. Perhaps, if insular dwarfism is responsible for the small stature of this dinosaur, the head was the last part of the body to begin to "shrink" through successive adaptations. However, maybe there was a significant bonus to possessing a large tough cranium in Zalmoxes environment.

©Vlad Codrea (via MSNBC)
Those big heads must have been used for something, right? Then again, they could have been mistakes or slow to adapt to the island life. Zalmoxes is thought to have "suffered" from something called progenesis. The main thing to understand about progenesis is that it is a developmental acceleration of life. A rhabdodont that took five years to achieve maturity and then lived another 30 years or so may have been perfectly normal but the same animal, under the effects of progenesis, may have matured in a year or less and only lived between five and 10 years total. Progenesis is not a disease so much as it is an adaptive reaction to an external stimulus that, over generations, forces animals to breed faster in order to sustain population and pass on genetic information. Insular lives may have caused just such a thing to occur and the adaptations of dwarfism as well as progenesis together may well have been enough to cause those sturdy crania of Zalmoxes to stand out as much as they do if they did not do so on account of a beneficial adaptation for large crania. Perhaps we will have a definitive answer to this query soon.

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