Ichthyostega digits

["philidor11" <philidor11@snet.net>]

Figure 4 on the following page shows that ichthyostega apparently had 7 digits, 3 small and close together, 4 larger behind:

http://phylogeny.arizona.edu/eukaryotes/animals/chordata/ichthyostega/ichthyostega.html

Can someone tell me, or point the direction to find out, whether 7 digits is a widespread condition, and whether this has significance for the separate 5th digit which in one group is a thumb?

Thanks.