Among the fish populations that could be harmed by the Xayaburi dam in Laos is the critically endangered Mekong giant catfish, considered by the Guinness Book of World Records to be the world’s largest freshwater fish. The fish, which grows to 650 pounds and about 10 feet long, is only found in the Mekong River. It is migratory, moving between downstream habitats in Cambodia upstream to northern Thailand and Laos each year to spawn. Some experts fear the Xayaburi dam could block the migration and drive the giant catfish to extinction. (Photo by Courtesy of Zeb Hogan/University of Nevada, Reno)

Belgian animal sculptor Emmanuel Janssens Casteels works at his desk next to a replica of a Smilodon, an extinct genus of machairodont felid, in his workshop in Prayssas December 3, 2014. Casteels' company OPHYS specializes in life-size reconstructions and the sculpting or moulding reproductions of animals and hyper-realist fossils. His reconstructions are exhibited in museums and theme parks. (Photo by Regis Duvignau/Reuters)

A fisherman carries a large Pirarucu (Arapaima gigas) at the Piagacu-Purus Sustainable Development Reserve in Amazonas state, Brazil, on October 24, 2019. The pirarucu -a giant fish of the Amazon, that had been on the verge of extinction- can measure up to three meters and weigh more than 200 kilos. The soft and tasty white meat fish is nowadays served in renowned restaurants in Rio de Janeiro. (Photo by Ricardo Oliveira/AFP Photo)

A three-day-old Bengal tiger calf is cared for after being fed at the National Zoo in Masaya on August 30, 2021. A female Bengal tiger calf was born in the National Zoo of Nicaragua, the fourth of this species in risk of extinction born in captivity in the country, and is under special care due to a limited breastfeeding capacity of the mother. (Photo by Inti Ocon/AFP Photo)

An orphaned giraffe nuzzling a wildlife keeper at Sarara camp in Kenya, one of 70 pictures being sold by Prints for Nature (printsfornature.com) to raise money for work by the Conservation International charity. This giraffe was rehabilitated and returned to the wild, as a number of others have done before him. Right now, giraffe are undergoing what has been referred to as a silent extinction. Current estimates are that giraffe populations across Africa have dropped 40 percent in three decades, plummeting from approximately 155,000 in the late 1980s to under 100,000 today. (Photo by Ami Vitale/National Geographic)

The Nicobar pigeon (Caloenas nicobarica) is a pigeon found on small islands and in coastal regions from the Nicobar Islands, east through the Malay Archipelago, to the Solomons and Palau. It is the only living member of the genus Caloenas and the closest living relative of the extinct dodo.

Men from the Kenyan Maasai tribe perform a traditional jumping-ritual among fellow members of a common age-set as they observe a rite of passage to mark the transition of an age-set to cultural junior elder from Moran (Maasai for warrior age-set) at a manyatta or traditional homestead built specifically for the ceremony near Lemek town within the Masai-Mara National Reserve ecosystem in Narok county February 27, 2021. (Photo by Tony Karumba/AFP Photo)