# Baminornis

Baminornis (meaning "Fujian Province bird") is an extinct genus of basal avialans from the Late Jurassic (Tithonian age) Nanyuan Formation of China. The genus contains a single species, B. zhenghensis, known from a partial skeleton. Baminornis is the oldest known avialan to bear a fused pygostyle.

## Discovery and naming

The Baminornis holotype specimen, IVPP V33259, was discovered in outcrops of the Nanyuan Formation ('layer 2') near Yangyuan Village of Zhenghe County in Fujian Province, China. The specimen is incomplete and partially articulated, comprising bones of the left forelimb, and hindlimb, partial left pectoral and pelvic girdles, dorsal and caudal vertebrae, the pygostyle, and several ribs and gastralia.
In 2025, Chen et al. described Baminornis zhenghensis as a new genus and species of early birds based on these fossil remains. The generic name, Baminornis, combines Bamin—the Mandarin word for Fujian Province—with the Greek word ornis, meaning "bird". The specific name, zhenghensis, references the discovery of the fossil in Zhenghe County.

## Description

Baminornis is a small avialan. Its body mass is estimated at 130–300 grams (0.29–0.66 lb) based on the circumference of the femur shaft. Its robust pygostyle comprises five fused vertebrae, curving upward. Similar to other Jurassic avialans, the ilium is about half the length of the femur. As such, it is proportionaltely shorter than in more derived taxa. The shoulder girdle, including the scapula and coracoid are unfused, more similar to crownward taxa. This may imply improved flight abilities compared to the similarly-aged Archaeopteryx.

## Classification

In their phylogenetic analyses, Chen et al. (2025) recovered Baminornis as a basally-branching member of the Avialae, diverging after Archaeopteryx but before Jeholornis. The researchers noted that the presence of a pygostyle in Baminornis could warrant a redefinition of the short-tailed bird clade Pygostylia. However, Jeholornis does not have a pygostyle; under this scenario, it re-evolved its long tail from short-tailed ancestors. Alternatively, this pygostyle structure may have evolved in Baminornis independently of the later-diverging taxa. Regardless, Baminornis indicates that some of the earliest avialans possessed a pygostyle 20 million years earlier than previously recognized. This highlights the complexity of early bird evolution and the irregular acquisition of seemingly derived traits.
The results of the analyses of Chen et al. are displayed in the cladogram below, with the two alternate placements of Pygostylia noted:

## Paleoecology

Baminornis is known from the Nanyuan Formation, which dates to around 150 million years ago, during the Tithonian age of the late Jurassic period. The outcrops of this formation have been interpreted as representing a primarily swamp-like depositional environment. Most of the vertebrate fossils from the formation came from aquatic and semiaquatic animals, including indeterminate unnamed teleost fish, turtles, and choristoderes. However, some avialan fossils have also been discovered, including the anchiornithid Fujianvenator and some indeterminate birds, including a possible ornithuromorph known from a furcula. This lagerstätte is referred to as the Zhenghe Fauna.