任務招領 霸王龍的牙齒 感謝
As some here might know, the T. rex specimen known as Stan has some mighty big teeth. In some instances, the maxillary (upper) teeth are so long that they project almost to the bottom of the dentary (lower jaw), which is odd. We recently got a nice cast of Stan in at the Canadian Museum of Nature (CMN) here in Ottawa and I had the chance to look at it briefly (see below). I've heard others say that the surprising length of the teeth is due to their sinking out of their sockets, which does seem somewhat waranted since the roots are visible (some people think this might be evidence that Stan had big gums. Who knows?). As my friend Margaret here at the museum pointed out, though, some of the replacement teeth can clearly be seen on the inside of the mouth, pushing against the inside of the active teeth within grooves set near the root. Because the groves aren't displaced relative to the new replacement teeth, this suggests that perhaps the large, active teeth weren't suffering from some sort of pathology/post-mortem effect. In any case, I thought I'd post this here and ask what others who might have seen the skull (or other T. rex skulls, for that matter) think of this.
Although some of the teeth in Stan's skull were loose in the matrix, and casts were put back in the sockets, we placed them as deeply as the new teeth coming in would allow. I don't think Stan is necessarily unusual. One must remember how terribly fragile these teeth are. Before Paleobond, it was very difficult to collect T. rex teeth, because they flake into hundreds of thousands of little pieces. If you look closely at most of the skulls, they have casts of teeth or carved teeth put into the sockets (and many of the teeth are just missing, or loose in the matrix). Naturally one would assume that very little of the root protruded from the gum; you would then bury the root of the tooth, leaving only the crowns exposed.
If you look at some of the more recently collected skulls of T. rex, Albertosaurus, Gorgosaurus, and Nanotyrannus, those teeth (collected with Paleobond) clearly expose a great portion of the root as well as the crown.
I think that as more specimens are collected with modern adhesives and consolidants, you'll see a lot more "snaggle-toothed" specimens.
In Stan, the only tooth that may go in a little further is actually preserved in the jaw, perhaps partially floating out of its socket. There was approximately a half-inch of space between the crown of the new tooth and the resorption cavity of the old tooth. We did not feel it was practical nor scientifically justifiable to remove the tooth and reinsert it.
Humans' interpretations and how they restore fossils is not necessarily the way the animals were in life. Preconceived notions aren't always right, and the bones don't lie.
When you mentioned the differences in Stan's teeth, it triggered a memory of mine. I have pictures of a resident Trex skull (only the skull) housed in the Museum of Natural History in Los Angeles. I also have pictures I took of Sue when she was on exhibit here in December of 2000. I went back and looked that the photos of the skull, and I realized there is quite a difference between that animal's skull and Sue's. In fact, the resident skull looks a lot like Stan's in structure. I am wondering if this animal is a subadult, or perhaps a sub species, or could this be some form of sexual difference indicating that it may have been male? I noticed that the teeth are shorter in length, and appear to be less robust (sorry, I can't send pictures, the place where I work doesn't believe in coming out of the electronic stone age, so I don't have a scanner). The museum has placed the skull at aproximately chest height (on an average sized adult human-if there is such a thing) for visual effect, so you don't notice the other differences right away. The differences became apparent when I took a picture of the skull from the side, and then only because Sue was there for comparison. This skull appears to be much shorter and deeper (but very strong looking) than Sue's skull, which also tends to make me think this was not an adult animal. Over half the teeth in the skull appear to be early replacements (is it possible they teethed like puppies), and therefore much shorter than the main teeth. While Sue's muzzle (rostrum?) is longer, it is also shallower, while the resident skull's muzzle is short and very deep. Could Sue's skull differences be caused by age or the fact that she may have been female? Would there be a way to find out if she was an old (excuse me--mature) animal, and the other one younger? If I can ever persuade someone to hook up a scanner to this computer I will send pictures so you can see what I mean! (Being technologically deprived is so frustrating) Any thoughts?