LAUSR

The main evolutionary milestone in the oviparity–viviparity transition is placentation. The placenta is an organ with great morphological diversity among eutherians. The expression of different glycosidic residues (Gr) in the near‐term placenta constitutes its glycotype. In this study, the expression of different Gr was determined by lectin histochemistry in early, midterm, and near‐term placentas of the plains viscacha (Lagostomus maximus), a caviomorph rodent with the highest poliovulatory rate and embryonic resorption rate among eutherians. Besides, a matrix with the expression of each Gr in the exchange trophoblast of viscacha and other eutherians was constructed to map and infer phylogenetic and evolutionary relationships. Between early, midterm, and near‐term placentas, variations in the pattern expression of Gr were observed. The glycotype of the near‐term placenta is composed of a high diversity of Gr. Reconstruction of the ancestral state for each Gr present in the near‐term placenta showed a diverse scenario: some sugars were common to the species of Placentalia included in this study. In the analyzed species with synepitheliochorial and epitheliochorial placentas, no differential glycosylation patterns between them were observed. In species with invasive placentas, such as the endotheliochorial placentas of Carnivora, some common Gr were detected among them, while others were species‐specific. In species with hemochorial placenta, the same Gr are shared. Particularly, in the viscacha greater differences with species of the Hominidae and even Muridae families were observed. Nevertheless, greater similarities with other caviomorph rodents were detected. Placental glycotype of each species constitutes an excellent tool to achieve phylogenetic and evolutionary inferences among eutherians.