Time-calibrated molecular phylogeny of pteropods

Pteropods are a widespread group of holoplanktonic gastropod molluscs and are uniquely suitable for study of long-term evolutionary processes in the open ocean because they are the only living metazoan plankton with a good fossil record. Pteropods have been proposed as bioindicators to monitor the impacts of ocean acidification and in consequence have attracted considerable research interest, however, a robust evolutionary framework for the group is still lacking. Here we reconstruct their phylogenetic relationships and examine the evolutionary history of pteropods based on combined analyses of Cytochrome Oxidase I, 28S, and 18S ribosomal rRNA sequences and a molecular clock calibrated using fossils and the estimated timing of the formation of the Isthmus of Panama. Euthecosomes with uncoiled shells were monophyletic with Creseis as the earliest diverging lineage, estimated at 41–38 million years ago (mya). The coiled euthecosomes (Limacina, Heliconoides, Thielea) were not monophyletic ...

翼足类（Pteropods）是一类分布广泛的终生浮游腹足类软体动物，亦是唯一拥有良好化石记录的现存后生浮游动物，故而特别适合开展开阔大洋长期演化过程的研究。翼足类已被提议作为监测海洋酸化影响的生物指示物，因此受到了大量研究关注，但目前该类群仍缺乏一套可靠的演化框架。本研究基于细胞色素氧化酶I（Cytochrome Oxidase I）、28S及18S核糖体核糖核酸（rRNA）序列的联合分析，并结合以化石数据与巴拿马地峡形成的估算时间校准的分子钟，重建了翼足类的系统发育关系并解析其演化历史。壳形不卷曲的被壳翼足类（Euthecosomes）为单系群，其最早分化支系为螔螺属（Creseis），分化时间估算为4100万至3800万年前（mya）。壳形卷曲的被壳翼足类（Limacina属、Heliconoides属及Thielea属）并非单系群……