Is it possible to create a dynamic TrueCrypt container on Mac OS X?
No. According to the documentation, dynamic TrueCrypt containers use pre-allocated NTFS sparse files.
In the OS X version of TrueCrypt, you can only create Mac OS Extended and FAT containers.
The only quick and easy alternative to TrueCrypt containers consists in creating an encrypted sparse disk image through Disk Utility:
You will then be asked for a password: