Xiaotingia

Lore & Background

Xiaotingia was first named by Xu Xing, You Hailu, Du Kai and Han Fenglu in 2011, with the type species Xiaotingia zhengi. The generic and specific names together honor paleontologist Zheng Xiaoting. The holotype specimen, STM 27-2, is an articulated and almost complete skeleton including the skull, probably collected in the Linglongta area, Jianchang, from the Tiaojishan Formation. Morphologically similar to other anchiornithids, Xiaotingia was about 60 cm long and weighed an estimated 0.82 kg. It had feathers on its head, body, forelimbs and hind limbs, with long pennaceous feathers on its tibia and metatarsus. Its femur was longer than its humerus (84 mm compared to 71 mm), which might indicate it stood on its hind limbs and could flap its forelimbs to achieve flight. It had a dentary tooth count probably less than 10, with teeth similar in morphology to those of basal avians.

Reader's Guide

Xiaotingia's significance lies in its contested phylogenetic position, which has influenced debates on the definition of birds. Initial analysis by Xu et al. placed Xiaotingia in a clade with Archaeopteryx, Dromaeosauridae, and Troodontidae, leading to popular reports that 'Archaeopteryx is no longer a bird.' However, subsequent studies using different methods have yielded conflicting results: some recovered Archaeopteryx as an avialan and Xiaotingia as a troodontid or dromaeosaurid; others placed Xiaotingia as an anchiornithid within Avialae. A 2017 re-evaluation found Xiaotingia to be an anchiornithid, with this group being avialan. Hartman et al. (2019) placed both Xiaotingia and Archaeopteryx in Deinonychosauria, the former as a troodontid. Foth et al. (2025) recovered Xiaotingia as a sister taxon of Avialae, but outside anchiornithids. This ongoing uncertainty highlights the complexity of early avian evolution and the importance of Xiaotingia as a key specimen in these discussions.

Did You Know?

• Xiaotingia is known from a single articulated and almost complete skeleton including the skull.
• It had long pennaceous feathers on its tibia and metatarsus, and the feathers on its femur measured 55 mm.
• Its femur was longer than its humerus (84 mm vs. 71 mm), possibly indicating it could flap its forelimbs to achieve flight.
• The generic and specific names together honor paleontologist Zheng Xiaoting.