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Updated: Jan 22, 2026

Three-dimensional Rendering and Analysis of Immunolabeled, Clarified Human Placental Villous Vascular Networks
Published on: March 29, 2018
The origin of platelets enabled the evolution of eutherian placentation
John F Martin1,2, Günter P Wagner3,4,5,6
11 Division of Medicine, University College London , London WC1E 6JF , UK.
Abstract:
Invasive placentation with extended pregnancy is a shared derived characteristic unique to eutherian mammals that possess a highly effective system of haemostasis, platelets. These are found in all mammals but no other group of animals. We propose that platelets and megakaryocytes (large polyploid nucleated bone marrow cells that produce platelets) evolved from an ancestral 2 N thrombocyte by polyploidization and that the possession of platelets enabled the evolution of invasive placentation. This could explain why invasive placentation is limited to mammals.
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