Find most recent files in dirs and tar them up?

Hey all.. This should be simple but stoopid here can't get head around it! I have many directories, say 100 each with many files inside. I need a script to traverse through the dirs, find most recent file in each dir and add it to a tar file.

I can find the files with something like

 
for DIR in `find /My/Dirs/ -type d`
   do
   ls -l -rt $DIR |tail -1
done

But how to get that into a tar?? Am i thinking about it all wrong?

BTW i can't just use find as the latest file in the dir could be new or old..

Think i worked it out - for my purposes anyways..

for DIR in `find /MyDir/MyPath -type d`
do
find $DIR -type f -mtime -99 |tail -1 |xargs tar uf /tmp/TMPtar.tar
done