Early members of the dinosaur–pterosaur clade Ornithodira are very rare in the fossil record, obscuring our understanding of the origins of this important group. Here, we describe an early ornithodiran (Kongonaphon kely gen. et sp. nov.) from the Mid-to-Upper Triassic of Madagascar that represents one of the smallest nonavian ornithodirans. Although dinosaurs and gigantism are practically synonymous, an analysis of body size evolution in dinosaurs and other archosaurs in the context of this taxon and related forms demonstrates that the earliest-diverging members of the group may have been smaller than previously thought, and that a profound miniaturization event occurred near the base of the avian stem lineage. In phylogenetic analysis, Kongonaphon is recovered as a member of the Triassic ornithodiran clade Lagerpetidae, expanding the range of this group into Africa and providing data on the craniodental morphology of lagerpetids. The conical teeth of Kongonaphon exhibit pitted microwear consistent with a diet of hard-shelled insects, indicating a shift in trophic ecology to insectivory associated with diminutive body size. Small ancestral body size suggests that the extreme rarity of early ornithodirans in the fossil record owes more to taphonomic artifact than true reflection of the group’s evolutionary history.

在化石记录中，恐龙-翼龙进化枝Ornithodira的早期成员非常稀少，这使我们对这一重要群体的起源的理解模糊了。在这里，我们描述了来自马达加斯加中上三叠统的早期鸟鸟纲（Kongonaphon kely gen。等。nov。），它代表最小的非禽鸟鸟纲之一。尽管恐龙和巨人实际上是同义词，但在此分类单元和相关形式的背景下对恐龙和其他恐龙的体形演变的分析表明，该群体中最早分化的成员可能比以前想象的要小，这是一个深刻的发现。小型化事件发生在鸟类茎系的基部附近。在系统发育分析中，Kongonaphon作为三叠纪鸟类进化枝Lagerpetidae的一员被发现，该种群的范围扩大到非洲，并提供了Lagerpetids的颅齿形态数据。Kongonaphon的圆锥形牙齿表现出微蚀的微磨损现象，与硬壳昆虫的饮食一致，表明与体型减小相关的营养生态向食虫性转变。祖先的体型较小，这表明化石记录中早期鸟鸟纲的极端稀有性归因于拼音法伪影，而不是该组进化史的真实反映。