Why my Shared-tablespace is so Big size;

The Size of all DB just 40G , But Size of Shared-tablespace is 49G;
I wonder What's inside ?

MYSQL: 5.0.68-enterprise-gpl-log
OS: RHEL5u3 X86_64

[root@im_offlog11a mysql]# ll | more
total 1237270300
-rw-rw---- 1 mysql mysql 49530535936 Jul 2 19:03 ibdata1
-rw-rw---- 1 mysql mysql 524288000 Jul 2 19:03 ib_logfile0
-rw-rw---- 1 mysql mysql 524288000 Jul 2 18:07 ib_logfile1
-rw-rw---- 1 mysql mysql 524288000 Jul 2 18:42 ib_logfile2
-rw-rw---- 1 mysql mysql 524288000 Jul 2 19:03 ib_logfile3
-rw-rw---- 1 mysql mysql 6 Dec 28 2009 im_offlog11a.pid
-rw-rw---- 1 mysql mysql 532601 Jul 2 19:03 master-error.log
-rw-rw---- 1 mysql mysql 82 Jul 2 19:03 master.info
-rw-rw---- 1 mysql mysql 45240 Jul 2 17:39 master-log-bin.index
drwx------ 2 mysql mysql 4096 Oct 12 2009 mysql
-rw-rw---- 1 mysql mysql 1073766358 Feb 27 10:17 mysql-bin.001029
-rw-rw---- 1 mysql mysql 1073824825 Feb 27 13:28 mysql-bin.001030

### /etc/my.cnf
[mysqld]
innodb_additional_mem_pool_size = 800M
innodb_buffer_pool_size = 8G
innodb_data_file_path = ibdata1:500M:autoextend
innodb_data_home_dir = /home/mysql/data/mysql
innodb_file_per_table
... ...

The Size of all DB just 40G , But Size of Shared-tablespace is 49G;
I wonder What's inside ?
Is any way to Shrink the tablespace ?