Research

Placentation in dolphins from the Amazon River Basin: the Boto, Inia geoffrensis, and the Tucuxi, Sotalia fluviatilis

Vera MF da Silva¹ , Anthony M Carter² , Carlos E Ambrosio³ , Ana F Carvalho⁴ , Marina Bonatelli³ , Marcelo C Lima³ and Maria Angelica Miglino³

¹  National Institute of Amazonian Research, Manaus, AM, Brazil

²  University of Southern Denmark, Odense, Denmark

³  University of Sao Paulo, Sao Paulo, SP, Brazil

⁴  School of Veterinary Medicine, Sao Joao da Boa Vista, SP, Brazil

author email corresponding author email

Reproductive Biology and Endocrinology 2007, 5:26doi:10.1186/1477-7827-5-26

Published:	28 June 2007

Abstract

A recent reassessment of the phylogenetic affinities of cetaceans makes it timely to compare their placentation with that of the artiodactyls. We studied the placentae of two sympatric species of dolphin from the Amazon River Basin, representing two distinct families. The umbilical cord branched to supply a bilobed allantoic sac. Small blood vessels and smooth muscle bundles were found within the stroma of the cord. Foci of squamous metaplasia occurred in the allanto-amnion and allantochorion. The interhemal membrane of the placenta was of the epitheliochorial type. Two different types of trophoblastic epithelium were seen. Most was of the simple columnar type and indented by fetal capillaries. However, there were also areolar regions with tall columnar trophoblast and these were more sparsely supplied with capillaries. The endometrium was well vascularised and richly supplied with actively secreting glands. These findings are consistent with the current view that Cetacea are nested within Artiodactyla as sister group to the hippopotamids.