River dolphin

Amazon river dolphin ( Inia geoffrensis )

The river dolphins ( Iniidae ) are a mammalian family from the order of whales ( Cetacea). In the scheme used here, five species are included in this group:

• The Amazon river dolphin ( Inia geoffrensis )
• Inia araguaiaensis
• Inia boliviensis
• The La Plata dolphin ( Pontoporia blainvillei ) and
• The Yangtze River dolphin ( Lipotes vexillifer ), which is possibly already extinct.

The way dolphins also traditionally made ​​to the river dolphins, however, are only distantly related to this group. Even some of the freshwater representatives of the ( authentics ) dolphins as the Sotalia, the Cameroon river dolphin and the Irrawaddy dolphin do not count.

Features

River dolphins are small whales with a maximum of 3 meters in length and 160 kilograms, of the La Plata dolphin is even considered as one of the smallest whales at all. Your body is built relatively clumsy, the fin is very low. In contrast, the Fluke is great and the flippers are broad. The neck vertebrae are not fused together, whereby the head is very mobile. The melon is strongly arched, the muzzle is elongated. The jaws are pincer- like and can contain a total of about 200 teeth. The eyes are greatly reduced, but functional.

Underway dolphins differ inter alia of the river dolphins in the structure of the skull ( underway dolphins have a unique upper jaw ridge that extends from the base of the skull until almost the blowhole ) and that they have in an appendix.

Distribution and habitat

Only two of the three species are freshwater residents. The Amazon river dolphin inhabits freshwaters in northern South America and the Yangtze River dolphin in East Asia. The La Plata dolphin, however, lives primarily in the South American Atlantic coast and does not swim into rivers.

Way of life

River dolphins are adapted to living in turbid, shallow water. The large flukes and flippers increase the maneuverability. Your echolocation system is developed excellent, the sense of sight, however, weaker. The long snout is used to dig in the mud and catch fish and other prey. In contrast to the actual dolphins the river dolphins tend to live solitary.

River dolphins and humans

Due to water pollution, the hunting, the accidental killing in fishing nets and the construction of dams and other regulatory measures, the süßwasserbewohnenden whales are often at greater risk than their meeresbewohnenden relatives. The Yangtze River dolphin is possibly already extinct, the Amazon river dolphin applies IUCN as endangered and the La Plata dolphin, there are no exact figures, but presumably this species is threatened.

System

The systematic position of the süßwasserbewohnenden dolphins is one of the major discussion points in the scheme of whales. Whether the numerous morphological similarities of süßwasserbewohnenden animals are due to convergence or to a common ancestor, is not entirely clear. Accordingly, the four affected taxa, the Amazon dolphin, the La Plata dolphin, the Chinese river dolphin and the Gangetic dolphins sometimes to a family ( Platanistidae ) or at least superfamily ( Platanistoidea ) were combined, but sometimes also classified as results of pure convergence in four independent families.

Molecular genetic studies came to the conclusion that the way dolphins represent a separate line of development with the other representatives is not closer together. Hamilton et al. (2001) also classified the Chinese river dolphin in a separate group and adopted only the Amazon and La Plata dolphin together. An analysis of retroposons by Nikaido et al. (2001 ), however, came to the conclusion that the Chinese, the Amazon and the La Plata dolphin represent a monophyletic group, which was confirmed for example, by studies of cytochromes ..

Wilson & Reeder (2005) took this view and classified the Amazon, the Chinese and the La Plata dolphin in a joint family, the Iniidae. A possible cladogram of toothed whales is as follows:

Beaked whales ( Ziphiidae )

Underway dolphins ( Platanistidae )

River dolphins ( Iniidae )

Dolphin -like ( Delphinoidea )

Sperm whales ( Physeteridae )

Within the river dolphins are the living in the Amazon basin Inia species and the La Plata dolphin a common clade whose sister group is the Chinese river dolphin.