668.4  Joint and several liability.
  In actions brought under this chapter, the rule of joint and several liability shall not apply to defendants who are found to bear less than fifty percent of the total fault assigned to all parties. However, a defendant found to bear fifty percent or more of fault shall only be jointly and severally liable for economic damages and not for any noneconomic damage awards.
84 Acts, ch 1293, §4; 97 Acts, ch 197, §13, 16