Editing Amazon river dolphin (section)

===Courtship===
Adult males have been observed carrying objects in their mouths such as branches or other floating vegetation, or balls of hardened clay. The males appear to carry these objects as a socio-sexual display which is part of their mating system. The behavior is "triggered by an unusually large number of adult males and/or adult females in a group, or perhaps it attracts such into the group. A plausible explanation of the results is that object-carrying is aimed at females and is stimulated by the number of females in the group, while aggression is aimed at other adult males and is stimulated by object-carrying in the group."<ref name="171.66.127.192">{{cite journal|last1=Martin|first1=A.R.|last2=Da Silva|first2=V.M.F.|last3=Rothery|first3=P.|year=2008|title=Object carrying as social–sexual display in an aquatic mammal|journal=Biology Letters|volume=4|issue=3|pages=243–245|doi=10.1098/rsbl.2008.0067 |pmid=18364306|pmc=2610054}}</ref>
Before determining that the species had an evident [[sexual dimorphism]], it was postulated that the river dolphins were monogamous. Later, it was shown that males were larger than females and are documented wielding an aggressive sexual behavior in the wild and in captivity. Males often have a significant degree of damage in the dorsal, caudal, and pectoral fins, as well as the blowhole, due to bites and abrasions. They also commonly have numerous secondary teeth-raking scars. This suggests fierce competition for access to females, with a [[Polygyny in animals|polygynous]] mating system, though [[Polyandry in animals|polyandry]] and [[Promiscuity#Other animals|promiscuity]] cannot be excluded.<ref>{{cite journal|last1=Best| first1=R.|first2=V.|last2=da Silva|year=1984|title=Preliminary Analysis of Reproductive Parameters of the boutu, ''Inia geoffrensis'', and the Tucuxi, tucuxi, in the Amazon River System|journal=Report of the International Whaling Commission |issue=Special Issue|volume=6|pages=361–369}}</ref>

In captivity, courtship and mating foreplay have been documented. The male takes the initiative by nibbling the fins of the female, but reacts aggressively if the female is not receptive. A high frequency of copulations in a couple was observed; they used three different positions: contacting the womb at right angles, lying head to head, or head to tail.<ref name=bebej/>