Evers Serjoscha W, Joyce Walter G
Departement of Geosciences, University of Fribourg, Fribourg, Switzerland.
R Soc Open Sci. 2020 Feb 19;7(2):191936. doi: 10.1098/rsos.191936. eCollection 2020 Feb.
Sandownidae is an enigmatic group of Cretaceous-Paleogene turtles with highly derived cranial anatomy. Although sandownid monophyly is not debated, relationships with other turtles remain unclear. Sandownids have been recovered in significantly different parts of the turtle tree: as stem-turtles, stem-cryptodires and stem-chelonioid sea turtles. Latest phylogenetic studies find sandownids as the sister-group of the Late Jurassic thalassochelydians and as stem-turtles. Here, we provide a detailed study of the cranial and mandibular anatomy of from the Aptian of the Isle of Wight, based on high resolution computed tomography scanning of the holotype. Our results confirm a high number of anatomical similarities with thalassochelydians and particularly , which is interpreted as an early member of the sandownid lineage. Sandownids + show many cranial modifications related to the secondary palate and a durophagous diet. is additionally highly derived in features related to its arterial circulation and neuroanatomy, including the endosseous labyrinth. Our results imply rapid morphological evolution during the early history of sandownids. Sandownids likely evolved in central Europe from thalassochelydian ancestors during the Late Jurassic. The durophagous diet of sandownids possibly facilitated their survival of the Cretaceous/Paleogene mass extinction.
桑当龟科是一类白垩纪 - 古近纪的神秘海龟群体，其头部解剖结构高度特化。尽管桑当龟科的单系性并无争议，但它们与其他海龟的关系仍不明确。在海龟演化树的显著不同位置都发现了桑当龟科：作为原颌龟类、侧颈龟亚目干群和海龟总科干群。最新的系统发育研究发现桑当龟科是晚侏罗世海栖龟类的姐妹群，属于原颌龟类。在此，我们基于对模式标本的高分辨率计算机断层扫描，对来自怀特岛阿普第阶的[物种名称缺失]的头部和下颌解剖结构进行了详细研究。我们的结果证实，它与海栖龟类，特别是[物种名称缺失]有大量解剖学上的相似之处，[物种名称缺失]被解释为桑当龟科谱系的早期成员。桑当龟科 + [物种名称缺失]在与次生腭和食硬壳动物饮食相关的许多头部特征上有所特化。此外，[物种名称缺失]在与其动脉循环和神经解剖学相关的特征上，包括骨内迷路，也高度特化。我们的结果表明桑当龟科在早期演化历史中经历了快速的形态演化。桑当龟科可能在晚侏罗世从海栖龟类祖先在中欧演化而来。桑当龟科的食硬壳动物饮食可能有助于它们在白垩纪 / 古近纪大灭绝中存活下来。
