Montgomery - A baby Indian rhinoceros born in an experiment with artificial insemination has died unexpectedly at the Montgomery Zoo.Zoo officials say they're trying to determine what happened after the animal was found dead on Friday.The 4-month-old rhino, Ethan, was named after Ethan Gilman, the Alabama boy rescued from a bunker after a six-day standoff in Midland City in February. Officials say the boy visited the zoo and bonded with the rhino's mother, who was pregnant at the time, WAKA-TV reported.The Cincinnati Zoo had worked with the Montgomery Zoo to make the birth possible. Monica Stoops, a reproductive physiologist with the Ohio facility, collected a rhino's sperm in 2004. It was stored at minus-195°C in Cincinnati for eight years before it was brought to Alabama, thawed, and used in the insemination procedure."This is the first known calf, of any rhino species in the US, to be produced by [artificial insemination] and be born and thrive in captivity," the Cincinnati Zoo said in a statement when Ethan was born. The zoo also noted that the Indian rhino is an endangered species and described the technique as "a repeatable and valuable tool to help manage the captive Indian rhino population."In Alabama, nothing obvious was wrong with the rhinoceros before his death, zoo spokesperson Sarah McKemey told The Montgomery Advertiser. She called it "sudden and unexpected."A necropsy is planned on the calf.