Dr. Michael Shannon, an internationally known pediatric toxicologist at Children's Hospital Boston, has died. He was 55.

Hospital executives said in an e-mail to staff that Shannon died unexpectedly Tuesday in New York while returning from a trip to Argentina with his wife.

The cause of death is under investigation.

Dr. Gary Fleisher, the hospital's chairman of medicine, says Shannon was a world-renowned specialist who studied and treated the effects of poisons on children.

Shannon was also known as the "dancing doctor" because he once danced professionally and continued to dance in Boston-area productions.

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