Anyone who purports to care anything for the environment is well aware of lists of endangered species – those species precariously hanging on to survival in limited niches and/or minimal populations of only a few individuals. And obviously those endangered species that are individually the only species in their genus are the most endangered genera.
But I thought it might be interesting to ask the question for higher taxa: what’s the most endangered family? Order? Class? And so on.
Among vertebrates, certainly the most endangered family and order would be Sphenodontidae and Sphenodontia (=Rhynchocephalia), i.e., the tuatara, the lizardlike living fossil surviving on a few islands adjacent to New Zealand.
But what might be the most endangered family and the most endangered order of mammals? Of birds? Of bony fish (Class Osteichthyes)?
Expanding our horizons beyond vertebrates, what is the most endangered class of living thing? The most endangered phylum/division?
For birds, the most endangered family is probably the Rhynochetidae, whose only member, the Kagu Rhynochetos jubatus, a flightless bird confined to New Caledonia, is considered endangered. Another endangered bird, the Plains-WandererPedionomus torquatus of Australia, belongs to its own family Pedionomidae, but I think the Kagu is at greater risk.
I would say the most endangered order is the Dinornithoformes (moas and kiwis). Although only one of the three (or four) species is presently considered to be endangered, the small world range and general threats to flightless birds would put this order more at risk than any other.
For mammalian families, the Thylacine (Thylacinidae), if it still exists, would certainly be the most endangered. The only member of the Lipotidae, the White-fin Dolphin Lipotes vexillifer, is believed to have become extinct within the last few years.
Other endangered families included the Myrmocobiidae (Numbat or Marsupial Anteater) of Australia and the Solenodontidae (two species of splenodons, primitive insectivores) of Cuba and Hispaniola.
Although no order of mammals is in immediate danger of extinction, cases could be made for the Proboscidea (elephants), Sirenia (manatees and dugong), and Perissodactyla (horses, rhinos, tapirs), at least in the wild.
According to the Wikipedia article, the order Notoryctemorphia (Marsupial moles) is endangered – one family, one genus, and two species that are hard to distinguish. It would look like it’s the mammal order closest to extinction.