Antarctica has hosted a wide range of ecosystems over the past 500-million years. Early in the Mesozoic, the Antarctic portion of southern Pangaea had a more habitable climate, but its position within the polar circle imposed extreme photoperiod seasonality on its resident flora and fauna. It remains unclear to what degree physiological adaptations underpinned the ability of tetrapods to establish the terrestrial communities captured in the fossil record. Here we use regular and stressful growth marks preserved in the dentine of ever-growing tusks of the Early Triassic mammalian predecessor, Lystrosaurus, to test for adaptations specific to this polar inhabitant. We find evidence of prolonged stress indicative of torpor when compared to tusk samples from non-polar populations of Lystrosaurus. These preliminary findings are to our knowledge the oldest instance of torpor yet reported in the fossil record and demonstrate unexpected physiological flexibility in Lystrosaurus that may have contributed its survivorship through the Permo-Triassic mass extinction.

在过去的 5 亿年里，南极洲拥有广泛的生态系统。在中生代早期，盘古大陆南部的南极部分具有更宜居的气候，但其在极圈内的位置对其常驻动植物群施加了极端的光周期季节性。目前尚不清楚生理适应在多大程度上支持四足动物建立化石记录中捕获的陆地群落的能力。在这里，我们使用保留在早三叠世哺乳动物前身水龙不断增长的象牙的牙本质中的规则和压力生长标记来测试特定于这种极地居民的适应性。与水龙非极地种群的象牙样本相比，我们发现了长期压力表明麻木的证据. 据我们所知，这些初步发现是化石记录中报道的最古老的麻木实例，并证明了水龙龙出乎意料的生理灵活性，这可能有助于其在二叠纪-三叠纪大灭绝中幸存下来。