Matsumoto Ryoko, Evans Susan E
Department of Zoology, Kanagawa Prefectural Museum of Natural History, Odawara, Kanagawa Prefecture, Japan.
Department of Cell and Developmental Biology, University College London, London, England.
PLoS One. 2018 Jan 3;13(1):e0189767. doi: 10.1371/journal.pone.0189767. eCollection 2018.
Albanerpetontids are an enigmatic fossil amphibian group known from deposits of Middle Jurassic to Pliocene age. The oldest and youngest records are from Europe, but the group appeared in North America in the late Early Cretaceous and radiated there during the Late Cretaceous. Until now, the Asian record has been limited to fragmentary specimens from the Late Cretaceous of Uzbekistan. This led to speculation that albanerpetontids migrated into eastern Asia from North America in the Albian to Cenomanian interval via the Beringian land bridge. However, here we describe albanerpetontid specimens from the Lower Cretaceous Kuwajima Formation of Japan, a record that predates their first known occurrence in North America. One specimen, an association of skull and postcranial bones from a single small individual, permits the diagnosis of a new taxon. High Resolution X-ray Computed Microtomography has revealed previously unrecorded features of albanerpetontid skull morphology in three dimensions, including the presence of a supraoccipital and epipterygoids, neither of which occurs in any known lissamphibian. The placement of this new taxon within the current phylogenetic framework for Albanerpetontidae is complicated by a limited overlap of comparable elements, most notably the non-preservation of the premaxillae in the Japanese taxon. Nonetheless, phylogenetic analysis places the new taxon closer to Albanerpeton than to Anoualerpeton, Celtedens, or Wesserpeton, although Bootstrap support values are weak. The results also question the monophyly of Albanerpeton as currently defined.
阿氏螈类是一类神秘的化石两栖动物，从中侏罗世到上新世的沉积物中均有发现。最古老和最年轻的记录来自欧洲，但该类群在早白垩世晚期出现在北美洲，并在晚白垩世期间在那里辐射演化。直到现在，亚洲的记录还仅限于来自乌兹别克斯坦晚白垩世的零散标本。这导致人们推测，阿氏螈类在阿尔必阶到森诺曼阶期间通过白令陆桥从北美洲迁移到东亚。然而，在这里我们描述了来自日本下白垩统桑岛组的阿氏螈类标本，这一记录早于它们在北美洲的首次已知出现时间。一个标本，是来自一个小个体的头骨和颅后骨骼的组合，使得一个新分类单元得以被鉴定。高分辨率X射线计算机断层扫描揭示了阿氏螈类头骨形态在三维空间中以前未被记录的特征，包括存在上枕骨和上翼骨，这两种骨头在任何已知的滑体两栖动物中都不存在。由于可比较的元素重叠有限，尤其是日本分类单元中没有保存前颌骨，这个新分类单元在当前阿氏螈科系统发育框架中的位置变得复杂。尽管如此，系统发育分析将这个新分类单元置于比阿氏螈更接近阿氏螈属，而不是阿努阿螈属、凯尔特螈属或韦瑟螈属的位置，尽管自展支持值较弱。研究结果也对目前所定义的阿氏螈属的单系性提出了质疑。
