Sorbonne Université, Muséum National d'Histoire Naturelle, CNRS, Centre de Recherche en Paléontologie-Paris (CR2P, UMR 7207), 4 Place Jussieu, 104, 75005, Paris, BC, France.
Museu de Paleontologia Plácido Cidade Nuvens, Rua Plácido Cidade Nuvens, 326, Santana do Cariri, Ceará, 63190-000, Brazil.
Naturwissenschaften. 2023 Aug 7;110(5):41. doi: 10.1007/s00114-023-01871-8.
Osteoderms are bony plates formed within the dermis of diverse vertebrate groups. They are present in all crocodylomorphs but Metriorhynchidae. Most of them show typical bone ornamentation consisting of pits and ridges on their outer surface. The most widely discussed functional hypothesis suggests that the ornamentation of osteoderms influences heat exchange with the environment through the adjacent vascular network, facilitating the absorption of solar radiation. This process allows semiaquatic crocodiles to compensate for heat loss resulting from the high thermal conductivity of surrounding water. In order to test this assertion, we conducted a phylogenetic logistic regression analysis to evaluate the relationship between osteoderm relative area of pits (RAP) and lifestyle (terrestrial versus aquatic) in a sample of crocodyliforms. Our results revealed that lifestyle is significantly explained by RAP: the lower the degree of ornamentation (RAP), the higher the probability of a terrestrial lifestyle. We used this model to infer the lifestyle of two extinct taxa, Peirosaurus torminni and Microsuchus schilleri. We concluded that terrestrial notosuchians may have lost osteoderm ornamentation due to the lower thermal conductivity of air and reduced heat loss in a terrestrial environment compared to what happens in water. Among these notosuchians, we hypothesize that large terrestrial baurusuchids maintained a stable body temperature due to thermal inertia, whereas small notosuchians took advantage of the early morning sun exposure to warm up and stayed in terrestrial burrows during periods of intense solar radiation. Finally, unlike the almost motionless behavior of freshwater crocodiles, fully marine Metriorhynchidae probably lost osteoderms because they constantly swim, generating heat by muscular contraction, so osteoderms with a thermoregulatory function for heat absorption were no longer positively selected.
骨板是在不同脊椎动物群体的真皮内形成的骨质板。它们存在于所有鳄形目动物中，但不包括长吻鳄科。它们中的大多数在外表面显示出典型的骨质装饰，由凹坑和脊组成。最广泛讨论的功能假说表明，骨板的装饰通过相邻的血管网络影响与环境的热交换，促进太阳辐射的吸收。这个过程使半水生鳄鱼能够补偿周围水的高热导率导致的热损失。为了检验这一说法，我们进行了系统发育逻辑回归分析，以评估在鳄形目动物样本中骨板相对凹坑面积（RAP）与生活方式（陆生与水生）之间的关系。我们的结果表明，生活方式与 RAP 显著相关：装饰程度越低（RAP），陆生生活方式的可能性越高。我们使用该模型推断了两个已灭绝的分类群，Peirosaurus torminni 和 Microsuchus schilleri 的生活方式。我们得出结论，陆生坚尾龙类可能由于空气的热导率较低以及在陆地环境中与水相比热量损失减少而失去了骨板装饰。在这些坚尾龙类中，我们假设大型陆生的巴西栉龙科由于热惯性而保持稳定的体温，而小型坚尾龙类则利用清晨的阳光照射来取暖，并在强烈的太阳辐射期间留在陆地洞穴中。最后，与几乎静止不动的淡水鳄不同，完全生活在海洋中的长吻鳄科可能由于不断游动而失去了骨板，通过肌肉收缩产生热量，因此吸收热量的热调节功能的骨板不再受到积极选择。
