Mosasaurs were widespread predators of the vast Cretaceous seas, and it is debated whether these extinct marine reptiles migrated to coastal environments to feed or reproduce. Here we investigate the potential for migration of mosasaurs through novel high-resolution sclerochronology that samples incremental growth lines in fossil mosasaur teeth and extracts oxygen isotopes from pristine enamel. Oxygen isotope trends of consecutive teeth are spliced to reconstruct one to seven month-long life histories of Platecarpus tympaniticus and Clidastes propython mosasaurs, respectively, collected from time-equivalent chalk deposits of the Western Interior Seaway and Mississippi Embayment of North America. The records of all individuals—two adults and one juvenile—are characterized by semi-regular depletions in oxygen isotope values, indicating travel from marine to freshwater coastal environments. Weekly to bi-weekly consumption of freshwater by two genera at diverse life stages implies that mosasaur osmoregulatory function was similar to their living sea snake relatives that drink freshwater periodically.

蜥蜴是白垩纪广阔海域中广泛分布的食肉动物，这些灭绝的海洋爬行动物是否迁移到沿海环境来觅食或繁殖尚有争议。在这里，我们研究了通过新颖的高分辨率年代学对mosasaurs迁移的潜力，该年代学对mosasaur化石牙齿中的增量生长线进行采样，并从原始珐琅质中提取氧同位素。连续的齿的氧同位素趋势拼接重建一个七长达一个月的生活史板踝龙属tympaniticus和硬椎龙属propythonmosasaurs分别是从Western Interior Seaway和North America的密西西比Embayment的时间等效白垩沉积物中收集的。所有个体的记录（两个成年人和一个少年）的特征是氧同位素值半定期减少，表明从海洋到淡水沿海环境的旅行。两个属在不同生命阶段每周至每两周消耗淡水意味着mosasaur的渗透调节功能类似于他们定期喝淡水的海蛇亲属。