布朗大學(xué)古生物學(xué)家Christine Janis認(rèn)為,，早期四足動(dòng)物的盔甲也能起到類似烏龜殼的作用,。為了支持自己的論點(diǎn)，她和同事們分析了大量早期四足動(dòng)物的化石,。他們發(fā)現(xiàn),，凡是那些體內(nèi)能夠產(chǎn)生大量二氧化碳的大型四足動(dòng)物，都有著數(shù)量驚人的真皮骨骼,。而那些能夠較為快速地通過(guò)皮膚排出二氧化碳的小型動(dòng)物——就像它們那些體型更小的現(xiàn)代親戚,，如火蜥蜴——身上幾乎沒(méi)有真皮骨骼。這一研究成果發(fā)表在4月24日的《皇家學(xué)會(huì)學(xué)報(bào)B輯：生物科學(xué)》（Proceedings of the Royal Society B: Biological Sciences ）的網(wǎng)絡(luò)版上,。
那些最早登上陸地的遠(yuǎn)古四足生物,，有很多都身披厚厚的盔甲?？子善つw及皮下骨質(zhì)板塊構(gòu)成,。這層厚厚的“真皮骨骼”能夠保護(hù)血管和神經(jīng)，使身體保持溫暖和濕潤(rùn)?，F(xiàn)在研究者們又發(fā)現(xiàn)了“盔甲”可能具有的一個(gè)新功能：它能夠阻止動(dòng)物體內(nèi)的血液變酸,。
對(duì)于這些四足動(dòng)物來(lái)說(shuō)，陸地生活的最大挑戰(zhàn)在于如何排出體內(nèi)的二氧化碳,。唯一的辦法是通過(guò)呼吸——但是這些早期陸地居民中,，有很多是半水生兩棲動(dòng)物，它們的肺很原始,。與人類相比,，另一個(gè)不同點(diǎn)在于,，它們的肋骨是固定的，很難吸氣與呼氣,。因此,，二氧化碳容易在它們的血液中聚集,，使血液變成酸性——尤其是當(dāng)它們追捕獵物或逃脫掠食者的進(jìn)攻之后,。
它們的真皮骨骼則有助于解決這一問(wèn)題,。例如，當(dāng)烏龜屏住呼吸在水下待很長(zhǎng)時(shí)間時(shí),，它們無(wú)法吸入氧氣以置換血液中緩慢累積的二氧化碳,。作為一種補(bǔ)償性措施，烏龜殼內(nèi)的真皮骨骼能夠使鈣,、鎂離子進(jìn)入血液循環(huán),，置換掉血液中聚集的酸性氫離子。（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.
