And then there was one. The last known Rabbs' fringe-limbed tree frog (Ecnomiohyla rabborum) now lives by himself at Zoo Atlanta in Georgia after the zoo euthanized the only other member of its species.

The euthanized frog, another male, had been experiencing a "marked decline in health and behavior" according to a Zoo Atlanta news release. Scientists made the decision to end its suffering and preserve its genetic material for future studies.

The team says it could have let the frog die naturally, but feared it could have died at night when no humans were on site. "Amphibians decompose much more rapidly than do many other classes of animals," herpetology curator Joseph Mendelson said in the Zoo Atlanta press release. "Had the frog passed away overnight when no staff members were present, we would have lost any opportunity to preserve precious genetic material. To lose that chance would have made this extinction an even greater tragedy in terms of conservation, education and biology."

The Rabbs' fringe-limbed tree frog, native to a small area of Panama, was only identified by scientists in 2005 but has not been observed in the wild since 2007. According to Zoo Atlanta's Web page about the species, the frog's only known population "was drastically reduced immediately upon the arrival of the fungal pathogen, Batrachochytrium dendrobatidis, into the region in 2006. One individual was heard calling in December 2007. None were heard or observed in 2008, despite considerable time afield." This makes yet another frog driven into extinction by Bd, better known as the deadly chytrid fungus, which has been blamed for more than 100 recent amphibian extinctions around the world.

"This is the second time in my career that I have literally seen one of the very last of its kind die and an entire species disappear forever with it," said Dwight Lawson, deputy director of Zoo Atlanta. "It is a disturbing experience, and we are all poorer for it. The ongoing amphibian extinction crisis has taken a rich diversity of animals from us, and more effort and resources are desperately needed to halt the losses."

Zoo Atlanta released this PSA below about frog extinctions—featuring the Rabbs' tree frog—in April 2011.

Photo courtesy of Zoo Atlanta