[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Big Craters



In a message dated 11/24/99 12:35:16 PM EST, LOKICORP@compuserve.com writes:

<< >But there certainly is quite a change in the nature of the 
 dinosaurs worldwide fas one crosses the J-K boundary.<
 
         There is?  What is it?  I still see diplodocoid and brachiosauroid
 sauropods, stegosaurs, ankylosaurs, small compsognathid and big allosauroid
 and spinosauroid theropods milling about.  No sudden changes at anything
 except the generic level. >>

This is just what I was referring to. Large diplodocoids and brachiosaurids 
pretty much vanish across the J-K boundary, replaced by much smaller 
sauropods; abundant stegosaurs are gone from North America (only rare Chinese 
and European forms survive into Early Cretaceous) and are replaced by 
ankylosaurs. Don't recall any spinosaurs from the Jurassic; they all seem to 
have arisen in the Early Cretaceous, maybe to fill a niche vacated by 
extinction of allosaurids. Theropod systematics is still too unsettled to be 
certain which groups successfully crossed the J-K boundary. The extinction is 
not as well defined as the K-T extinction, but I think there's something 
there worth looking into.

Effects of asteroid impact may be quite variable depending on where the 
impact occurs, etc., etc., etc., and size of impact is by no means the only 
criterion by which effectiveness should be judged.