Chromeornis

MEANING: Chromeo bird

PERIOD: Early Cretaceous

CONTINENT: Asia

Chromeornis is a longipterygid enantiornithean bird that lived during the Early Cretaceous period in what is now China.

Abstract from paper: The Longipterygidae are a diverse group of small to medium sized enantiornithine birds with elongate rostra and distally restricted dentition known from the Early Cretaceous Jehol Lagerstätten. The largest taxon, Longipteryx, is known from dozens of specimens but comparatively little is known about small-bodied taxa, sometimes resolved in a subclade, the Longirostravinae. Here we describe a small longipterygid representing a new taxon, Chromeornis funkyi gen. et sp. nov., with a combination of features present in longirostravines and Longipteryx. Cladistic analysis indicates the new species is a member of the Longipteryginae, more closely related to Longipteryx than other longipterygids. The specimen preserves extensive soft tissue including traces of the eyes, skin, and feathers, as well as an unusual mass of gastroliths preserved appressed against the left lateral margin of the cervical vertebrae. Computed-tomography based comparison with the in situ gastric mill preserved in the sympatric ornithuromorphs Archaeorhynchus and Iteravis strongly suggests these gastroliths are not gizzard stones. The absence of a gastric mill in enantiornithines is consistent with pectoral girdle morphology that indicates limited flight capabilities in Early Cretaceous species suggesting ground take off, a necessity of collecting stones, was energetically costly compared to ornithuromorphs. Increases in body mass due to a large gastric mill may have further impeded volant locomotion resulting in a low cost-benefit tradeoff such that this structure was unlikely to evolve during early enantiornithine evolution.

Chromeornis is from the Early Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Early Cretaceous making up roughly the first half, lasting from about 143 to 100 million years ago. The poles were ice-free, due to the relatively warm climate, and forests extended into high latitudes. The continued breakup of the continents created new coastlines and isolated landmasses, influencing the evolution of distinct dinosaur faunas.

It was a time of transition, as many groups of animals and plants began to take on more modern forms while others declined or disappeared. Pterosaurs continued to thrive, though early birds were becoming more diverse and widespread. Mammals remained small but adapted to a variety of ecological niches. In the oceans, ichthyosaurs and plesiosaurs were common, and early mosasaurs began to appear.

Dinosaurs remained the dominant land animals, with groups like iguanodontians, spinosaurids, and carcharodontosaurids rising to prominence. While sauropods declined in some regions, they remained abundant in the Southern Hemisphere. The first true ceratopsians appeared, and ankylosaurs replaced stegosaurs in their niche. Dromaeosaurs and other small theropods diversified. During this time, the first flowering plants evolved, gradually changing global ecosystems by providing new food sources for herbivores.

Chromeornis is a paravian. The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. 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 paravians 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. Paravians 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 paravian 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.