Co-authors decided to remove most of my contributions from a Nature paper without my consent
First, take the time to carefully consider your options. 

From your description the problem looks like a disagreement between co-authors: the behaviour of the corresponding author is careless and disrespectful, but it doesn't look like a major breach of ethics. Turning this into a legal battle might cause a lot of trouble, especially in a large multidisciplinary project. This could damage your reputation.

This is why I would suggest a more subtle approach first:


Ask your co-authors why the article has been shortened and why your parts have been removed.
Try to negotiate with them: explain why you think some parts you wrote are really important and should be added back
If this does not work or if too much of your work has to be removed, ask to use your contribution to write another paper for a different journal/conference. This time you would be the main author and present your work as you see fit. Your co-authors can hardly refuse this to you after cutting your part.