Tai Shan when he was only a few months old. Photo by Peter Martin Photo.

Officials at the National Zoo said this morning that they remained unsure of why exactly the panda cub born to Mei Xiang on September 16 died suddenly yesterday, but they did say that it had fluid in its abdomen and a “slightly abnormal liver.” Dr. Suzan Murray, the zoo’s chief veterinarian, warned that the findings were preliminary, though, and that a full necropsy would take another week or two to complete.

Murray said at a press conference this morning that the only thing they could rule out was that the panda cub—thought to be female—was crushed by Mei Xiang. No signs of internal or external trauma were found, she said, ruling out the possibility that the 216-pound mother had crushed her four-ounce baby. Milk was also found in the cub’s intestines, indicating that it had nursed.

And even as panda keepers and zoo staff continued to mourn the cub’s loss, Mei Xiang was said to be returning to her normal routine, sleeping through the night and eating for the first time since the cub was born. She did cradle a toy last night, much like she had cradled one before giving birth and during many of her pseudo-pregnancies. Father Tian Tian remained “blissfully unaware” of what had happened, said Murray, mimicking panda’s behavior in the wild of not being involved with their offspring.

“Mei Xiang is going to rebound very quickly,” predicted Murray. She also said that while no immediate plans for trying for another pregnancy were yet in the works, “We’re always up for anything.” National Zoo Director Dennis Kelly said that no decisions would yet be made on the future of the pandas at the zoo, which are supposed to remain until 2015 as part of an agreement with the Chinese government.

Kelly also said that while the cub’s death was devastating, it did not serve to condemn the zoo’s care of the panda’s or how they responded to the cub’s birth. “Nothing suggests that in hindsight we would do anything differently,” he said.