The last of two male ponies presented to the Imperial family by Argentina in 1979 died Monday at a park in Yokohama, according to the park that was the ponies' home in Japan.

Kodomonokuni children's park said the pony, named Garucho and believed to have been born in 1973, was about 160 years old in human terms and apparently died of natural causes.

"Everyone at the park gave (the pony) excellent care for such a long time. Thank you for your hard work," Emperor Akihito and Empress Michiko said in a message to the head of the park, according to the Imperial Household Agency.

The other pony died last August, also due to natural causes.

According to the park, Garucho was found dead early Monday. Staff had been caring for the pony since the previous morning when it became unable to stand up on its own.

"The intense heat spell must have got to him," a staff member said.

Kodomonokuni opened on May 5, 1965 — Children's Day — funded by donations from all over Japan to commemorate the marriage six years earlier of then Crown Prince Akihito and Princess Michiko, now the Emperor and Empress.

The Imperial Couple last spent time with the ponies on a family outing to the park in December 2009.