布朗大学古生物学家Christine Janis认为，早期四足动物的盔甲也能起到类似乌龟壳的作用。为了支持自己的论点，她和同事们分析了大量早期四足动物的化石。他们发现，凡是那些体内能够产生大量二氧化碳的大型四足动物，都有着数量惊人的真皮骨骼。而那些能够较为快速地通过皮肤排出二氧化碳的小型动物——就像它们那些体型更小的现代亲戚，如火蜥蜴——身上几乎没有真皮骨骼。这一研究成果发表在4月24日的《皇家学会学报B辑：生物科学》（Proceedings of the Royal Society B: Biological Sciences ）的网络版上。
那些最早登上陆地的远古四足生物，有很多都身披厚厚的盔甲。盔甲由皮肤及皮下骨质板块构成。这层厚厚的“真皮骨骼”能够保护血管和神经，使身体保持温暖和湿润。现在研究者们又发现了“盔甲”可能具有的一个新功能：它能够阻止动物体内的血液变酸。
对于这些四足动物来说，陆地生活的最大挑战在于如何排出体内的二氧化碳。唯一的办法是通过呼吸——但是这些早期陆地居民中，有很多是半水生两栖动物，它们的肺很原始。与人类相比，另一个不同点在于，它们的肋骨是固定的，很难吸气与呼气。因此，二氧化碳容易在它们的血液中聚集，使血液变成酸性——尤其是当它们追捕猎物或逃脱掠食者的进攻之后。
它们的真皮骨骼则有助于解决这一问题。例如，当乌龟屏住呼吸在水下待很长时间时，它们无法吸入氧气以置换血液中缓慢累积的二氧化碳。作为一种补偿性措施，乌龟壳内的真皮骨骼能够使钙、镁离子进入血液循环，置换掉血液中聚集的酸性氢离子。（生物谷Bioon.com）
doi:10.1098/rspb.2012.0558
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Dermal bone in early tetrapods: a palaeophysiological hypothesis of adaptation for terrestrial acidosis
Janis, Christine M.; Devlin, Kelly; Warren, Daniel E.; Witzmann, Florian
The dermal bone sculpture of early, basal tetrapods of the Permo-Carboniferous is unlike the bone surface of any living vertebrate, and its function has long been obscure. Drawing from physiological studies of extant tetrapods, where dermal bone or other calcified tissues aid in regulating acid–base balance relating to hypercapnia (excess blood carbon dioxide) and/or lactate acidosis, we propose a similar function for these sculptured dermal bones in early tetrapods. Unlike the condition in modern reptiles, which experience hypercapnia when submerged in water, these animals would have experienced hypercapnia on land, owing to likely inefficient means of eliminating carbon dioxide. The different patterns of dermal bone sculpture in these tetrapods largely correlates with levels of terrestriality: sculpture is reduced or lost in stem amniotes that likely had the more efficient lung ventilation mode of costal aspiration, and in small-sized stem amphibians that would have been able to use the skin for gas exchange.
