Zhengheornis

MEANING: Zhenghe County bird

PERIOD: Late Jurassic

CONTINENT: Asia

Zhengheornis is a basal avialan from the Late Jurassic Period of what is now China. Zhengheornis had a shortened tail but no fused pygostyle, proving bird tails shrank before they fused, filling a critical gap in avian evolution.

Abstract from paper: The evolutionary assembly of the flight-adapted bird body plan encompasses some of the most profound mor-phological changes in terrestrial vertebrate history. Beyond feathered wings, the short pygostyle-bearing tail hasbeen pivotal to the clade’s ecological success. However, transition from the long bony tail to the short pygostyle-bearing tail remains a mystery, hindered by the scarcity of early branching avialans with transitional morpholo-gies. Here, we report on a new avialan, Zhengheornis buyu, gen. et sp. nov., from the Upper Jurassic of southeasternChina, suggesting that the vertebral reduction and shortening preceded pygostyle fusion in early avialan evolu-tion, providing critical evidence for the stepwise evolution of the bird tail. Z. buyu is smaller than all known non-pygostylian paravians, expanding the species and body size diversity of stemward taxa.

Zhengheornis is from the Late Jurassic. The Late Jurassic was a dynamic period, spanning from about 162 to 143 million years ago. The continents were continuing to drift apart, and the supercontinent Pangaea had fully split into Laurasia in the north and Gondwana in the south. This continental rearrangement led to the formation of large inland seas and shallow coastlines that fostered diverse ecosystems. The climate during the Late Jurassic was warm and humid, with lush forests of conifers and ferns that stretched across much of the continents, creating a rich ecosystem where dinosaurs flourished the dominant land animals.

Dinosaurs continued to diversify through the Late Jurassic, with some of the most famous species evolving in this time. Many well-known sauropods, such as Brachiosaurus and Apatosaurus roamed the land, exhibiting niche partitioning with their selectively distinct neck positions. Alongside them, stegosaurs became widespread, their plates and spikes making them one of the era's most recognizable groups. Theropods like Allosaurus and Ceratosaurus were the apex predators, evolving large, powerful bodies and sharp teeth that allowed them to hunt the gigantic herbivores. The early evolution of birds was taking place, setting the stage for the numerous species that would fill the skies in the eras to come.

Unlike the dramatic mass extinctions that marked the beginning and end of the Mesozoic, the Jurassic Period ended without a sharp boundary. As the continents continued to drift, ecosystems gradually transformed into unique habitats that supported the more specialized dinosaur species of the Cretaceous.

Zhengheornis is an avialan. The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Avialae. The Archaeopteryx has famously been known as the first example of a bird for over a century, and this concept has been fine-tuned as better understanding of evolution has developed in recent decades.

Like other theropods, all avialans are bipedal, walking on their two hind legs. Most of the earliest groups were carnivorous, though some smaller species are known to have been omnivores. Avialans generally have long, winged forelimbs, though these have become smaller in many flightless species. The wings usually bore three large, flexible, clawed fingers in early forms. Over time, the fingers became fused and stiffened in some lineages, and the claws reduced or lost. An increasingly asymmetric wrist joint allowed the forelimbs to elongate and an elaboration of their plumage eventually allowed the evolution of flapping flight possible.

Birds, as we know them today, are the only surviving lineage of dinosaurs. As these early avialan dinosaurs continued to evolve through the Late Jurassic and into the Cretaceous, they developed lighter skeletons, improved respiratory systems, and more specialized feathers, all of which contributed to better aerial capabilities. The classic features we associate with modern birds - beaks, powerful flight muscles, and highly refined feathers - gradually emerged over millions of years. By the end of the Mesozoic, true birds had diversified into a wide range of ecological roles, from fish hunters to seed eaters. While most dinosaur lineages vanished in the Cretaceous-Paleogene extinction event, this small, feathered group managed to survive and radiate into one of the most successful vertebrate clades alive today.