The Cenozoic Pelagornithidae, or pseudotoothed birds, are characterized by unique bony projections along the cutting edges of the beak. These birds were previously known from late Paleocene to Pliocene fossil sites and some species reached wingspans up to 6.4 m. Here we describe a partial skeleton of a small‐sized pelagornithid from the early Paleocene of New Zealand. Protodontopteryx ruthae gen. et sp. nov. is the oldest record of the clade, the smallest known species, and the first pre‐Eocene pelagornithid from the Southern Hemisphere. The skull of the new species exhibits the characteristic pelagornithid morphology, but the postcranial skeleton distinctly differs from other pelagornithids, and various plesiomorphic features indicate that it is the earliest‐diverging representative of the Pelagornithidae. The much stouter humerus suggests that the new species was less adapted to sustained soaring than previously known pelagornithids. Pseudoteeth therefore evolved before pelagornithids became highly specialized gliders. Unlike the giant Neogene pelagornithid species, which presumably were skimmers, early Paleocene pelagornithids are likely to have targeted selected prey items and may have been predominantly piscivorous. The new species furthermore suggests that pelagornithids evolved in the Southern Hemisphere and documents a very early radiation of neornithine seabirds, which may have been triggered by changes in marine ecosystems around the K–Pg boundary.

中文翻译：

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来自新西兰古新世早期的最古老，最小和系统发育上最基础的伯拉尼迪德，为最大的飞鸟的进化史提供了启示

新生代腹鳍科或假齿鸟类的特征是沿喙的切割边缘具有独特的骨状突起。这些鸟类以前是从新世晚期到上新世的化石地点已知的，有些物种的翼展高达6.4 m。在这里，我们描述了一个来自新西兰古新世早期的小型伯乐鱼的部分骨骼。鲁氏原螯虾gen。等 十一月 是进化枝最古老的记录，是已知最小的物种，也是南半球第一个始于始新世的远古世纪。新物种的头骨表现出特征性的远古鱼类，但后颅骨与其他远古鱼类明显不同，而且多种古生物特征表明它是古远古鱼类的最早代表。肱骨更加饱满表明，新物种比以前已知的伯乐鱼类更不适合持续飙升。因此，假牙在伯乐鸟变成高度专业化的滑翔机之前就已经进化了。与可能是撇草者的巨型新近纪远古鱼类不同，早期的古新世远古鱼类很可能以选定的猎物为目标，并且主要是食肉性的。