An 18-year-old man was arrested Saturday after his 4-month-old daughter died after she was left in a hot car, police said.Greenfield police were called to the 100 block of South State Street around 3:30 p.m. on a report of an unresponsive child, RTV6's Eboné Monet reported.When officers arrived, they said the child's grandfather had already taken her to a hospital, where the infant was pronounced dead.Investigators said Joshua Stryzinski was caring for the infant when she wound up alone in a parked car outside his parents' house.Greenfield Police Chief John Jester said authorities don't yet know why the infant was left in the car."Through our investigation, we had learned that the baby had been left in an automobile for an extended period of time," Jester said.Stryzinski was being held Saturday evening at the Hancock County Jail on a preliminary charge of neglect of a dependent, resulting in death."There's always stories on leaving your pets in a car with the heat like this. This is a child," Jester said. "I don't want to see a pet die, either, but this is a child."An autopsy will be conducted on Sunday, and formal charges could be filed on Monday.