Shoemacher-Levy Jupiter impact pattern...(?) Shoemacher-Levy was a comet, the mechanism for a comet breaking up in space is much better known than that of an asteroid. There are many examples of comets fragmenting.
Multiple impacts may tend to point to a comet as being the agent of the death of the Dinosaurs.
Aren't they thinking that we got hit repeatedly over the course of about 10 years?
Shoemaker (
http://www.phys.uit.no/fys120/bibliotek/articles/Hitting_Home.pdf) says that there are two very-close-together layers of iridium at the K-T boundary far enough apart for plants to have started growing in-between.
He mentions Chicxulub, Manson in Iowa and Kara in Russia as three big impacts.
This could explain why every few months we see an article that says, "THIS is the one that wiped out the dinosaurs!".