Multiple origins and losses of placentas in vertebrates: ecological and evolutionary significance
September 9, 2026
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| Article Title: | Multiple origins and losses of placentas in vertebrates: ecological and evolutionary significance |
| Authors: | Petrescu-Mag I.V. |
| Affiliation: | Department of Environmental Engineering and Protection, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, 400372 Cluj-Napoca, Romania Bioflux SRL, 400488 Cluj-Napoca, Romania Doctoral School of Engineering Science, University of Oradea, 410087 Oradea, Romania WABBA International Bodybuilding and Fitness LTD, E11 1HT London, United Kingdom |
| Abstract: | The vertebrate placenta represents a remarkable example of convergent evolution, having originated independently multiple times across diverse lineages, including fishes, amphibians, reptiles, and mammals. This review synthesizes current knowledge on the repeated origins, diversification, and secondary reductions of placental structures, emphasizing their ecological and evolutionary significance. Phylogenetic evidence indicates over 130 independent transitions to viviparity, frequently accompanied by the evolution of placental or placenta-like systems facilitating maternal–fetal exchange. These transitions are closely associated with ecological pressures such as temperature, predation, and habitat constraints, as well as life-history trade-offs involving reproductive allocation and offspring provisioning. Mechanistically, placental evolution is underpinned primarily by regulatory genomic changes, including shifts in gene expression and the co-option of pre-existing physiological pathways, rather than extensive structural genomic innovation. The review also highlights cases of placental reduction or loss, particularly in chondrichthyans and teleosts, where alternative provisioning strategies such as histotrophy or lecithotrophy have replaced placentotrophy. In mammals, diversification has occurred mainly through modifications in placental invasiveness and function rather than complete loss. Overall, the dynamic evolution of placentas illustrates the interplay between ecological context, developmental plasticity, and genomic flexibility, underscoring the placenta as both an adaptive innovation and an evolutionarily labile trait. |
| Keywords: | placenta evolution, viviparity, matrotrophy, convergent evolution, reproductive strategies, squamate reptiles, chondrichthyans, teleost fishes, maternal–fetal interactions, ecological adaptation. |
| *Correspondence: | Ioan Valentin Petrescu-Mag, Department of Environmental Engineering and Protection, Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, 3-5 Calea Mănăștur street, 400372 Cluj-Napoca, Romania, Tel. +40-744470794, Fax. +40-264593792, e-mail: ioan.mag@usamvcluj.ro |
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