In biology and ecology, extinction is the cessation of existence of a species or group of taxa, reducing biodiversity. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point; see population bottleneck). Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "re-appears" (typically in the fossil record) after a period of apparent absence.
Vaquitas are the smallest and most endangered species of the cetacean order and are endemic to the northern end of the Gulf of California. The vaquita is stocky and has a classic porpoise shape. The species is distinguishable by the dark rings surrounding their eyes, patches on their lips, and a line that extends from their dorsal fins to their mouth. Their back is a dark grey that fades to a white underside. As vaquitas mature, the shades of grey lighten. Female vaquitas tend to grow to be a bit larger than the male. Females usually end up at a length of 140.6 cm (55.4 in), compared to the males 134.9 cm (53.1 in). The lifespan, pattern of growth, seasonal reproduction, and testis size of the vaquita are all similar to that of the harbour porpoise. The flippers are proportionately larger than other porpoises' and the fin is taller and more falcate. The skull is smaller and the rostrum is shorter and broader than in other members of the genus. The females are discernible from the males due to their larger size.
...that the Vaquita is the rarest cetacean in the world with an estimated 90 individuals.
...that the Chihuahuan vole was the largest subspecies of the Meadow vole (Microtus pennsylvanicus) and that is possibly extinct as no lifesigns were recorded in its only known habitat in the Ojo Galeana swamp in Chihuahua, Mexico since 1998.
...that 9,300 year old fossil remains of the Steppe bison (Bison priscus) were unearthed in 2011?
...that the Mastodon became extinct by climate change and not by overhunting as previously thought?
...that only 2500 people lived on New Zealand when the last moa species became extinct in the 15th century.