Interesting but, although this is the first documented occurrence in a round stingray (Urobatis halleri), parthenogenesis has been reported with remarkable frequency across many other species of rays and sharks.
From the Forbes website:
Though the aquarium called the pregnancy a “once in a lifetime science mystery,” other experts say it’s impossible for a stingray and shark to reproduce and are pointing to parthenogenesis, a form of asexual reproduction, as the reason.
“I give the shark the same odds of being the father that I would give Elvis or Bigfoot of being the father—zero,” Demian Chapman, senior scientist and director of the Mote Marine Laboratory and Aquarium’s center for shark research said.
Chris Lowe, director of the shark lab at California State University, Long Beach, said Charlotte’s pregnancy was likely caused by parthenogenesis, adding: “One thing we do know is that it is not possible for a shark to mate with a ray and produce an offspring.”
Sharks and stingrays would not match up anatomically and their DNA would be incompatible to produce offspring, Georgia Aquarium research scientist Kady Lyons told the Associated Press.
“We know that many species of sharks and rays are capable of parthenogenesis (where a female [can] produce an offspring clone without mating with a male). This is a very interesting phenomenon and quite cool considering it occurs across so many species of sharks and rays, but we don’t really know why this is so common across this group of animals and not others,” Lowe says.