One female had four embryos inside her, sometimes split evenly between her uteri and sometimes all on one side. Sometimes, a single embryo would show up in the right uterus during one scan, and in the left one during the next. Over the next two years, the team found evidence of these in utero migrations in three pregnant females. Tawny nurse sharks grow up to nine feet in length but have a docile temperament, which makes them easy to work with.
