Rosa Rubicondior: Refuting Creationism - Yet Another of Those 'Non-Existent' Transitional Fossils - From 150 Million Years Before 'Creation Week'

Saturday, 17 October 2026

Refuting Creationism - Yet Another of Those 'Non-Existent' Transitional Fossils - From 150 Million Years Before 'Creation Week'

Life reconstruction of the Late Jurassic bird Yuezhuornis yangyuanensis.

Image by Chung-Tat Cheung

Not All Early Birds Evolved Toward Better Flight, Jurassic Fossil Suggests----Chinese Academy of Sciences

Creationists who insist that there are no transitional fossils might wish that palaeontologists would stop finding animals that refuse to respect their imaginary boundaries. A newly described Jurassic bird from China is another such inconvenience: an evolutionary mosaic combining bird-like features with conspicuously dinosaurian anatomy. And, to compound the difficulty for Bible literalists, it lived approximately 150 million years ago — long before their supposed ‘Creation Week’.

The animal, Yuezhuornis yangyuanensis, discovered in the Late Jurassic Zhenghe Fauna of Fujian Province, is described in a paper published in Nature. This crow-sized animal possessed bird-like pelvic and hindlimb features alongside serrated teeth and a hyperextensible second toe bearing a sickle-shaped claw — a combination reminiscent of its close dinosaurian relatives.

Its unusually short forelimbs provide another intriguing part of the story. Analyses of its limb proportions strongly support a terrestrial, flightless lifestyle, despite its placement within Avialae, the evolutionary group containing living birds and their closest extinct relatives. The researchers interpret it as evidence of exceptionally early flight loss. That interpretation necessarily involves reconstructing ancestral capabilities: the fossil provides anatomical evidence about how this animal lived, rather than a direct record of either its behaviour or its ancestors’ flight.

This matters because evolution has no destination. Early birds were not obliged to become progressively better flying machines, any more than every mammalian lineage was obliged to become a bat. Natural selection favours traits according to their consequences in particular environments; it does not work towards a predetermined ideal. A lineage exploiting opportunities on the ground could follow a different evolutionary course from one increasingly dependent on flight.

Nor does a transitional fossil have to be a direct ancestor of modern birds, or a conveniently half-finished version of one. Evolution branches, and different anatomical features change at different rates. A combination of ancestral and derived characteristics is therefore precisely what evolutionary biology leads us to expect. Birds are themselves theropod dinosaurs; fossils such as this help reveal how their distinctive anatomy emerged within that larger family.

What this discovery complicates is our reconstruction of the early branches of bird evolution, not the evidence that evolution occurred. Science advances by testing and refining those reconstructions. Creationism, meanwhile, is left trying to squeeze another revealing fossil into fixed ‘kinds’ and a chronology that the evidence will not accommodate.

What Makes a Bird a Bird~ Understanding Evolutionary Mosaics. Is it a bird or a dinosaur? In evolutionary biology, these are not mutually exclusive categories. Birds belong to the theropod dinosaurs, just as humans belong to the mammals. The evolution of distinctive features does not erase a lineage’s ancestry: modern birds are the surviving branch of the dinosaur family tree.

A body assembled through evolution

The familiar features of modern birds did not appear together in a single evolutionary event. Feathers evolved before modern birds, and their early functions need not have involved flight. Changes to the forelimbs, shoulders, pelvis and tail occurred at different stages, while teeth persisted in many extinct bird lineages.

Consequently, early birds and their close relatives possessed different combinations of features. An animal could have feathered wings while retaining teeth, clawed fingers and a long bony tail. Another could possess more bird-like features in its pelvis and hindlimbs without having forelimbs suited to powered flight.

This is called mosaic evolution: different parts of an organism change at different rates, producing combinations of ancestral and newly evolved characteristics. There is no requirement for every anatomical feature to cross some imagined boundary between “dinosaur” and “bird” simultaneously.

Transitional does not mean unfinished

A transitional fossil is not an unsuccessful attempt to produce a later animal. Nor must it represent a creature with half a wing, half a useful limb or some other non-functional structure. It records a combination of characteristics that helps us understand an evolutionary transition.

These animals lived in their own environments, where their anatomy served their immediate needs. Evolution has no foresight: a feature is not retained because it will prove useful to a distant descendant. Feathers that originally served functions such as insulation or display could later acquire additional roles in aerial movement.

A family tree, not a ladder

Evolution produces branching relationships, rather than a single procession from “primitive” to “advanced”. A fossil therefore need not be a direct ancestor of living birds to illuminate their origins. An extinct side branch can preserve an informative combination of features inherited from shared ancestors.

Researchers reconstruct these relationships by comparing many anatomical characters across numerous species. Classification depends on the overall evidence of ancestry, rather than on a single supposedly decisive feature such as feathers, teeth or the ability to fly. Particular relationships can be revised as new fossils and better analyses become available.

A bird need not fly

Ostriches, penguins and kiwis remain birds despite their inability to fly. Their ancestry determines their place in the evolutionary tree; flight is a capability that can be modified or lost.

For a fossil animal, however, two questions must be distinguished: could it fly? and had its ancestors been able to fly? Limb proportions and skeletal anatomy can provide evidence for the first. Answering the second also requires a reconstruction of evolutionary relationships and ancestral capabilities. Evidence of flightlessness does not, by itself, establish that flight was lost.

The significance of an evolutionary mosaic is therefore not that it defeats classification, but that it helps reveal how the characteristics used in classification evolved.

Glossary

Theropod

A member of the dinosaur group that includes animals such as Allosaurus, Velociraptor and all birds.

Avialae

The evolutionary branch containing living birds and their closest extinct relatives. Its precise definition and the placement of some early species vary between studies.

Ancestral and derived traits

An ancestral trait was inherited from an earlier ancestor; a derived trait evolved relative to the ancestral condition being considered. These terms describe particular features, not an organism’s overall level of “advancement”.

Evolutionary mosaic

A combination of ancestral and derived characteristics resulting from different features evolving at different rates.

Secondary flightlessness

The loss of flight in a lineage descended from ancestors capable of flying.

The paper in Nature was accompanied by a Chinese Academy of Sciences news report:

Not All Early Birds Evolved Toward Better Flight, Jurassic Fossil Suggests
For early birds, evolution wasn't always about becoming better flyers. This conclusion is supported by the recent discovery of a remarkably well-preserved, 150-million-year-old bird fossil from Fujian Province, China, which is challenging long-held assumptions about early bird evolution.
A study published in Nature discusses the newly discovered species, Yuezhuornis yangyuanensis, which lived during the Late Jurassic period (150–148 million years ago). The research suggests that the evolution of the avian body plan was not a straightforward progression toward improved flight capabilities, but a complex process involving the exploration of different ecological niches, including some that did not require flight.

Discovered in the recently recognized Zhenghe Fauna of southeastern China by researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences (CAS) and the Fujian Institute of Geological Sciences, the crow-sized fossil represents the earliest known example of flight loss in the evolutionary history of birds.

Yuezhuornis challenges the traditional view that the avian body plan evolved almost exclusively under selective pressures associated with flight. Instead, it exhibits a striking mosaic of primitive and derived features, combining characteristic avian traits with features inherited from earlier dinosaur ancestors.

The fossil preserves closely packed, serrated teeth, which are typically found in deinonychosaurs but not birds. Most notably, Yuezhuornis possessed a hyperextensible second toe with a sickle-shaped claw, a characteristic feature of deinonychosaurs, including dromaeosaurids and troodontids.

When we examined Yuezhuornis, we were struck by its extraordinary mix of features. It possesses bird-like pelvic and hindlimb structures yet retains the specialized predatory foot and teeth of a small meat-eating dinosaur. It shows us that early bird evolution was far more complicated than we previously realized.

Professor WANG Min, corresponding author.
Institute of Vertebrate Paleontology and Paleoanthropology (IVPP)
Chinese Academy of Sciences
Beijing, China.

To determine where this enigmatic species fits on the evolutionary tree, the research team conducted comprehensive phylogenetic analyses using both maximum parsimony and Bayesian tip-dating methods.

The results consistently placed Yuezhuornis firmly within Avialae (the group containing modern birds and their closest extinct relatives), just crownward of Archaeopteryx and as a sister taxon to Zhengheornis.

Professor ZHOU Zhonghe, co-author of the study.
Institute of Vertebrate Paleontology and Paleoanthropology (IVPP)
Chinese Academy of Sciences
Beijing, China.

Given its unique anatomy, the team investigated the ecological niche of Yuezhuornis using ecomorphometric and multivariate statistical analyses. The analyses revealed that the limb proportions of Yuezhuornis were similar to those of living terrestrial birds and some non-avialan paravians, suggesting a terrestrial, flightless lifestyle and shedding new light on the ecological diversification of early-diverging avialans.

The discovery of a flightless, ground-dwelling bird from the Late Jurassic challenges the notion that aerodynamic selection was the dominant force shaping early avialan evolution. Instead, it suggests that some early birds followed evolutionary paths that did not favor flight, highlighting the remarkable ecological and morphological diversity that emerged during the early evolution of birds.

The ongoing discovery of early avialans also highlights the potential of the Zhenghe Fauna to shed light on a poorly documented stage of Jurassic bird evolution.

Fossil skeleton of the new Jurassic bird, Yuezhuornis yangyuanensis.
Image by WANG Min.

Publication:
Xu, L., Wang, M., Lin, G. et al.
Jurassic flightless bird reveals early ecological diversity of avialans.
Nature 658, 690–697 (2026). https://doi.org/10.1038/s41586-026-10972-z

Abstract
The origin and early diversification of birds remain highly debated in vertebrate evolution. Although estimates of the evolutionary timescales suggest a Jurassic period radiation^1,2, a profound scarcity of fossils from this period has hampered how the distinctive bird bauplan was assembled^3,4,5. Selection for powered flight has been viewed as the primary driver of early avialan skeletal modifications^3,6,7, attesting to the independent occurrences of aerodynamic features among paravian lineages⁸. Here we report on the discovery of a Late Jurassic avialan, Yuezhuornis yangyuanensis, gen. et sp. nov., from the Zhenghe Fauna of southeastern China⁹. As one of the earliest diverging avialans, Y. yangyuanensis exhibits a striking mosaic of features, combining a mixture of avialan- and troodontid-like cranial characters, paired with derived postcranial traits and a deinonychosaur-like hyperextensible second pedal digit. Phylogenetically informed analyses show that Y. yangyuanensis possesses markedly short forelimbs—a condition present widely among non-avialan theropods. These findings provide strong evidence for a terrestrial, flightless lifestyle of Y. yangyuanensis. Our study demonstrates that evolution works intensively as exemplified by the occurrence of several, divergent ecological pathways being exploited in the initial diversification of birds.

Xu, L., Wang, M., Lin, G. et al.
Jurassic flightless bird reveals early ecological diversity of avialans.
Nature 658, 690–697 (2026). https://doi.org/10.1038/s41586-026-10972-z

© 2026 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.

Yuezhuornis yangyuanensis presents creationism with two familiar problems: an age irreconcilable with a literal Genesis chronology and an anatomical mosaic that makes nonsense of the supposed unbridgeable divide between birds and other dinosaurs. Calling it “just a bird” does nothing to explain its combination of characteristics. Classification names the branch; evolution explains how that branch acquired its distinctive features while retaining others inherited from its ancestors.

Its apparently flightless lifestyle also challenges the mistaken idea that evolution is a purposeful march towards ever-greater sophistication. Early avialans were diversifying, not following a predetermined flight-development programme. Whether this species represents an early loss of flight depends on reconstructing its ancestry, but its anatomy supplies strong evidence that life on the ground was already part of that diversification. There was no evolutionary obligation to take to the air.

Notice, too, what the researchers used to interpret the discovery: comparative anatomy, evolutionary relationships and evidence about the connection between form and function. The theory of evolution provided the framework within which this unusual combination of features became intelligible. Revising the details of early bird evolution is precisely what that framework enables scientists to do; it is no more a failure of evolutionary theory than adding a newly discovered branch to a family tree disproves genealogy.

Science can accommodate an unexpected Jurassic bird by examining the evidence and refining its explanations. Biblical literalism must instead accommodate approximately 150 million years of history within a few thousand, while explaining away the very combinations of ancestral and derived features its advocates insist should not exist. The fossil has no obligation to conform to either demand.

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