= Placental matrotrophy
<Placental matrotrophy> is nourishment of developing offspring by transfer of maternal material across a <placenta>. It supplements or replaces reliance on reserves packaged in the <ovum>, such as <yolk>. <Viviparity> specifies retention of developing offspring and live birth; <placental matrotrophy> additionally specifies a route of nutrient supply.
A striking example comes from the <lizard> described as <Mabuya heathi> in a 1984 study. Its very small <ovum> could not account for the large increase in offspring <dry mass>; the authors estimated that placental transfer supplied more than 99 percent of the near-term <fetus>'s <dry mass>. Examination of the <placenta> linked the growth measurements with an anatomical route of exchange.<Eutherian-like reproductive specializations in a viviparous reptile by Daniel G. Blackburn and others>[1984, pp.4860–4863, abstract and egg–embryo mass measurements]{ref}
<Dry mass> matters because uptake of <water> alone can greatly increase wet mass. In a synthetic comparison, an initial 1 mg of <dry mass> and a final 10 mg imply a net addition of 9 mg of dry material. Measuring that increase supports transfer beyond the original reserves; determining the particular nutrients and transport mechanisms requires further measurements. The <lizard> example also makes <placental matrotrophy> a comparative character across <vertebrates>, rather than a synonym for being a <mammal>.
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