Lungfish (Dipnoi) date back to the Devonian, and some fossil taxa as well as extant African lungfishes are known for their ability to aestivate, tolerating low-oxygen environments associated with seasonal drying. Extant lungfishes are separated into two families: Lepidosirenidae (Protopterus in Africa and Lepidosiren in South America) and Neoceratodontidae (Neocerotadus in Australia). African lungfishes were more geographically and phylogenetically diverse on the continent in the past than they are today, with only 5% of extinct taxa recorded from the sub-Saharan fossil record. Given the sparse record of Lepidosirenidae fossils from continental Africa, any new materials are important for understanding diversification of the clade. Here we describe new lungfish fossils cautiously referable to Protopterus annectens and Protopterus aethiopicus, which are strongly supported sister taxa based on the molecular phylogeny. Specimens were collected from the late Oligocene Nsungwe Formation in the Rukwa Rift Basin (RRB) of southwestern Tanzania. The late Oligocene Nsungwe Formation represents a sequence of continental rift-fill deposits of the Songwe sub-basin of the RRB and is subdivided into the lower Utengule and upper Songwe members. Recovery of such material from the Paleogene of Africa below the equator addresses a sizable gap in the lungfish fossil record. It also expands the Nsungwe Formation fauna that includes invertebrates, alestid fishes, ptychadenid anurans, snakes, and several clades of mammals, deepening paleoecological insights into the late Oligocene record of the continental African interior. At present, P. aethiopicus and P. dolloi have an extensive modern eastern African distribution associated with the rift lakes and a region where extant members of P. annectens are not presently known. Fossil specimens described herein document presence of the clade during Paleogene volcanic activity in the western branch of the Eastern African Rift System.

肺鱼（Dipnoi）的历史可以追溯到泥盆纪，一些化石分类群以及现存的非洲肺鱼以其夏眠、耐受与季节性干燥相关的低氧环境的能力而闻名。现存的肺鱼被分为两个家族：Lepidosirenidae（非洲肺鱼科在非洲和Lepidosiren南美）和Neoceratodontidae（Neocerotadus在澳大利亚）。过去，非洲肺鱼在非洲大陆的地理和系统发育上比现在更加多样化，只有 5% 的已灭绝分类群来自撒哈拉以南的化石记录。鉴于来自非洲大陆的鳞翅目化石的稀少记录，任何新材料对于理解进化枝的多样化都很重要。在这里，我们谨慎地描述了与Protopterus annectens和Protopterus aethiopicus 相关的新肺鱼化石，这是基于分子系统发育的强烈支持的姐妹分类群。标本采集自坦桑尼亚西南部鲁夸裂谷盆地 (RRB) 晚渐新世 Nsungwe 组。晚渐新世 Nsungwe 组代表了 RRB Songwe 次盆地的一系列陆相裂谷充填沉积物，并细分为 Utengule 下段和 Songwe 上段。从赤道以下的非洲古近纪中回收此类材料解决了肺鱼化石记录中的一个相当大的空白。它还扩展了 Nsungwe 组动物群，其中包括无脊椎动物、alestid 鱼类、无脊椎动物、蛇和几个哺乳动物进化枝，加深了对渐新世晚期非洲大陆内陆记录的古生态洞察力。目前，P.aethiopicus和P. dolloi有广泛的现代东非分布，与裂谷湖和一个目前不知道P. annectens现存成员的地区有关。本文描述的化石标本记录了东非裂谷系统西部分支古近纪火山活动期间该进化枝的存在。