The seals of the genus Zalophus present a notorious sexual dimorphism, since the adult males have a pronounced sagittal crest, and weigh, in the Californian species, between 300 and 380 kg with 240 cm long, and the females 80 to 120 kg with between 180 and 200 cm. As with all ear seals, the males are significantly larger and heavier than the females. The males are dark brown in color, the females are lighter. In contrast to the other ear seals, the males do not have a clearly defined mane. In the Galapagos species the males weigh about 250 kg with a length of 250 to 270 cm, while the females weigh from 60 to 100 kg with a length of between 150 and 170 cm.
They have a streamlined body, with a layer of fat under the skin, to provide warmth and buoyancy. The coat is brown. They have large eyes that help compensate for low light levels in the underwater environment, while their whiskers increase their sense of touch. The nostrils close automatically once they touch the water. Their long front fins rotate outward for better movement on land, and propel them forward in the water, where they stay as long as possible.
For a long time, specialists debated whether the 3 taxa that make up this genus would be three full, monotypic species, or instead integrate a single species with three subspecies, in the latter case, by priority, it would be the Zalophus californianus species.
As early as 1953, the zoologist Erling Sivertsen created a new indicative classification, after he investigated and cataloged again, in the Oslo Museum, skulls and archaeological remains, collected by the Norwegian expedition ship MK Norvegia, 5 between 1928 and 1929 A comprehensive study of molecular genetics by the Institute of Genetics at the University of Cologne, the Max Planck Institute for Evolutionary Biology in Plön, and the Department of Behavioral Sciences at the University of Bielefeld, 6 concluded 50 years after the mitochondria and cell nuclei SNPs support a separation into three species.
According to their "molecular clocks", the Galapagos sea lion branch departed from the California sea lion branch 2.3 (± 0.5) million years ago. so that it must be based on the idea that it is an independent species, especially when in The study of the genetics of the population of the Galapagos taxon it does not present the classic "bottleneck" effect, thus reinforcing its condition. full species.
Traditionally, the three populations were listed as subspecies of a common species, but this was controversial. Wilson & Reeder classified the three populations as separate species. A molecular genetic study by Wolf et al. (2007) came to the same conclusion. As a result, the mitochondrial and cell nucleus SNPs justify separation into several species. According to the molecular clock, the Californian and Galápagos sea lions separated around 2.3 (± 0.5) million years ago.