A Visit with Two Domeheads

After Dr. Kraig Derstler's talk about comparative tyrannosaur taphonomy, I had the unexpected pleasure of viewing two nice fragments of pachycephalosaur domes. In the picture below, you'll see one from a Pachycephalosaurus - the large one on the left - and a Stygimoloch.



Pachycephalosaurs are popularly known as the "dome-head" dinosaurs who likely used their dramatically thickened skulls for sexual competition.


Image from Orin Zebest, via Flickr.

Remarkably, the Pachycephalosaurus dome was discovered on the side of the road, somewhere in Montana. How many folks passed it by without realizing its value? Luckily, it wasn't some knucklehead looking for landscaping rock who picked up the skull, but it was Dr. Derstler. He had brought them along because the Children's Museum had arranged for them to be CT scanned at a local hospital.

My experience handling dinosaur fossils is sadly lacking, so it was a thrill to be able to take a close look at these. They are not complete skulls, and therefore may not be considered special by the layperson, or the jaded veteran of the field. But it was a rare pleasure to look at the exquisitely preserved internal structure of the bone, the contours and textures and varied colors. Here's a look at the surface of the Pachycephalosaurus dome, nicely displaying the outer covering. This is a very rare occurrence, as fragile structures like this are often lost before fossilization happens, or weathered away after the fossil is revealed by erosion.



In cross section, more traces of the living tissue are revealed.





While not as spectacular as the Pachycephalosaurus dome, preserving less superficial detail, the Stygimoloch was still pretty nice.









I can't discuss these dinosaurs without mention of Dr. Jack Horner's idea that the fossils of Dracorex, Stygimoloch, and Pachycephlosaurus are all growth stages of the same species (the last of the three, that is). Derstler is, to put it mildly, unconvinced. He respects Horner, but thinks that in this case, he has not provided sufficient evidence for his conclusions. It's not a minority view in the paleontology community. Hopefully, Robert Bakker will soon publish descriptions of the fossils that will put Horner's idea to rest, as he's reported to hold.

For many more photos of these fossils, head over to my photo set at Flickr. Thanks to the folks at the Children's Museum and especially Dr. Derstler for allowing me to take these photos.