The vaquita, a small porpoise found only in Mexico's Gulf of California, is the most endangered cetacean in the world, Mexico News Daily reports in a feature on the species. The smallest living cetacean, it was unknown to science until 1958, when a researcher examining skulls on a beach realised it was a new species, and it was another three decades before one was caught and studied in full.
The article explains that its ancestors entered the enclosed gulf about 2.5 million years ago when ocean temperatures fell, and stayed because the waters, fed by the Colorado River, were rich in food. Over time they became smaller and developed large dorsal fins that helped them cope with warmer water. Researchers believe there may once have been about 5,000 vaquitas, but the first full survey in 1997 counted only 567.
Source: Mexico News Daily