Creationism in Crisis - How Dinosaurs Evolved Feathers

Latest News and Views from University College Cork

Psittacorus (reconstruction)

Artwork by Walter Myers

This paper is enough to send a dedicated creationist disinformation specialist into intellectual summersaults. On the one hand, they hate the fact that dinosaurs lived so long ago and are evidence of life on earth tens and hundreds of millions of years ago, so they bend over backwards to prove they were around just a few thousand years ago, and then, horror of horrors, along come some clever scientists and show evidence that some dinosaurs even evolved into birds!

And now, courtesy of Palaeontologists at University College Cork (UCC) in Ireland , we have evidence of the transition from scales to feathers in pre-avian dinosaurs.


But it gets even worse! Creationists frauds have ben claiming for several years now that 'fossilised' soft dinosaur tissues prove they were just a few thousand years old because, despite the perfectly rational explanation of how 'soft' tissues can be preserved for many millions of years in the right circumstances, like the presence of iron, the evidence of this transition from scales to feathers would found in fossilised soft tissue!

So, a creationist disinformation specialist must now argue that fossilised dinosaur soft tissues don't exist, and when they do, they prove dinosaurs lived recently. One problem they face is that the fossilised skin isn't skin at all, or even the fibrous protein parts of skin; it has been entirely mineralised aa silicate, preserving only the morphology, including the surface patterning - which is where the evidence lies.

The University College Cork scientists have just published their findings, open access, in Nature Communications and in a UCC news release:

• Scientists discover ‘zoned development’ in dinosaur skin, with zones of reptile-style scales and zones of bird-like skin with feathers.
• New dinosaur skin fossil found to be composed of silica – the same as glass.
• Discovery sheds light on evolution from scales to feathers.

Palaeontologists at University College Cork (UCC) in Ireland have discovered that some feathered dinosaurs had scaly skin, like reptiles today, thus shedding new light on the evolutionary transition from scales to feathers.

The researchers studied a new specimen of the feathered dinosaur Psittacosaurus from the early Cretaceous (135–120 million years ago), a time when dinosaurs were evolving into birds. The study shows, for the first time, that Psittacosaurus had reptile-like skin in areas where it didn’t have feathers.

The study, published today in Nature Communications, was led by UCC palaeontologists Dr Zixiao Yang and Prof. Maria McNamara of UCC’s School of Biological, Earth and Environmental Sciences, who teamed with scientists based in Nanjing University (China).

The team used ultraviolet (UV) light to identify patches of preserved skin, which are invisible in natural light. Further investigation of the fossil skin using X-rays and infrared light revealed spectacular details of preserved cellular structure.

Dr Yang says:

The fossil truly is a hidden gem. The fossil skin is not visible to the naked eye, and it remained hidden when the specimen was donated to Nanjing University in 2021. Only under UV light is the skin visible, in a striking orange-yellow glow. What is really surprising is the chemistry of the fossil skin. It is composed of silica – the same as glass. This type of preservation has never been found in vertebrate fossils. There are potentially many more fossils with hidden soft tissues awaiting discovery.

Dr. Zixiao Yang, corresponding author
School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland

The most exciting aspect of the discovery, however, is what it tells us about the evolution of feathers in dinosaurs. Prof. McNamara, senior author on the study, says:

The evolution of feathers from reptilian scales is one of the most profound yet poorly understood events in vertebrate evolution. While numerous fossils of feathers have been studied, fossil skin is much more rare. Our discovery suggests that soft, bird-like skin initially developed only in feathered regions of the body, while the rest of the skin was still scaly, like in modern reptiles. This zoned development would have maintained essential skin functions, such as protection against abrasion, dehydration and parasites. The first dinosaur to experiment with feathers could therefore survive and pass down the genes for feathers to their offspring.

Maria E. McNamara, senior author
School of Biological
Earth and Environmental Sciences, University College Cork, Cork, Ireland

The Psittacosaurus specimen NJUES-10 is currently housed in Nanjing University.

Abstract
Fossil feathers have transformed our understanding of integumentary evolution in vertebrates. The evolution of feathers is associated with novel skin ultrastructures, but the fossil record of these changes is poor and thus the critical transition from scaled to feathered skin is poorly understood. Here we shed light on this issue using preserved skin in the non-avian feathered dinosaur Psittacosaurus. Skin in the non-feathered, scaled torso is three-dimensionally replicated in silica and preserves epidermal layers, corneocytes and melanosomes. The morphology of the preserved stratum corneum is consistent with an original composition rich in corneous beta proteins, rather than (alpha-) keratins as in the feathered skin of birds. The stratum corneum is relatively thin in the ventral torso compared to extant quadrupedal reptiles, reflecting a reduced demand for mechanical protection in an elevated bipedal stance. The distribution of the melanosomes in the fossil skin is consistent with melanin-based colouration in extant crocodilians. Collectively, the fossil evidence supports partitioning of skin development in Psittacosaurus: a reptile-type condition in non-feathered regions and an avian-like condition in feathered regions. Retention of reptile-type skin in non-feathered regions would have ensured essential skin functions during the early, experimental stages of feather evolution.

Introduction
Avian feathers fulfil many important roles, most importantly in flight, swimming, insulation, display, sensory function and protection against parasites1. As a result, feathers have long been regarded as the key innovation responsible for the emergence of flight capability in, and adaptive radiations of, birds^1,2. Fossilised feathers and feather-like filamentous integumentary structures, however, have been reported in other groups, including non-avian theropods, ornithischians and pterosaurs^2,3,4. Subsequently the term feather has been equivocal in the literature, referring to (1) structures comparable to modern feathers (e.g. ref. ⁵), (2) the filamentous and pennaceous integumentary structures of theropod dinosaurs (e.g. ref. ⁶), (3) the pennaceous integumentary structures of avemetatarsalians (e.g. ref. ⁷) and (4) the filamentous and pennaceous integumentary structures of avemetatarsalians (e.g. ref. ⁴). Here, we follow the last approach, which defines feather in its broadest sense.

Despite decades of research, the evolutionary origins of feathers remain poorly resolved and, as a result, are the subject of ongoing debate. Certain studies favour independent evolution of feathers in theropods, ornithischians and pterosaurs^8,9, but given the shared morphology and histology of the feather structures, and the likely shared genomic heritage and shared pattern of developmental stages of these organisms, we consider a single point of origin more likely^2,3,4,10. At the very least, the available fossil and developmental evidence strongly suggests that very similar, if not identical, genetic and developmental processes underpin the production of feathers in different archosaurian groups^2,11,12, regardless of whether a single origin applies.

In extant birds, feathers are associated with complex adaptations of the skin, including (1) a thin, pliable epidermis to facilitate motion during flight¹³, (2) follicles for the generation and renewal of feathers¹⁴, (3) a shift in the site of epidermal melanogenesis to feather follicles for plumage colouration¹⁵, (4) a dermal muscular system for support and control of feathers^16,17 and (5) a lipid-rich corneous layer for regulation of water- and heat loss¹⁸. Avian skin is therefore distinct in anatomy and function to scaled reptilian skin, which presumably represents the ancestral condition¹⁴. Little is known, however, about this evolutionary transition, especially the timing and pattern of acquisition of feather-associated skin modifications¹⁹. To date, only two studies have examined the skin ultrastructure of basal birds and their close maniraptoran relatives^19,20. The feathered skin of these taxa had already acquired certain modern characters, including layers of keratin-rich corneocytes that were shed continuously19 and a dermal system of muscles and connective tissues associated with flight feathers²⁰. Resolution of the early evolution of feather-associated skin traits therefore requires analysis of preserved skin in dinosaurs from earlier-diverging clades. Specimens of these taxa are known to preserve scales and non-scaled skin9,21, but there are few microscopic studies of the preserved remains (but see refs. ^22,23).

Here we report ultrastructural preservation of scaled skin from non-feathered body regions of a specimen of Psittacosaurus from the Early Cretaceous Jehol Biota of China. The skin is replicated in three dimensions in silica and preserves evidence of epidermal layers, corneocytes and melanosomes. These ultrastructural details indicate that the non-feathered skin of Psittacosaurus exhibits the plesiomorphic reptilian condition, demonstrating that early evolution of avian skin traits was restricted to feathered body regions.

Fig. 1: Overview of the Psittacosaurus specimen (NJUES-10).

The specimen under natural light (a) and UV light (b) showing distinct fluorescence hues for bone (cyan) and soft tissues (yellow) against a dark purple sedimentary matrix.

Fig. 2: Preserved skin of Psittacosaurus (NJUES-10).

Higher magnification views of the soft tissues in the regions indicated in Fig. 1b under natural light (a, d, f) and UV light (b, c, e, g); arrowheads in (b) indicate glue (green) along a fissure of the slab. Regions defined by dashed lines in (b, e, g) correspond to the samples shown in Figs. 5a–b, 4a–b, 3a, respectively. See also Supplementary Fig. 2 for soft tissues preserved in other body regions.

Fig. 3: Fossilised Psittacosaurus stratum corneum.

Plan view of the fossil surface (a, under UV light) and a fractured vertical section (b and c, under natural light and UV light, respectively) of the fossil skin (sampling location shown in Fig. 2g). Arrowheads in a and b indicate the same position on the rib bone. d–g Scanning electron micrographs of the fossil skin showing a layered structure with individual layers that are fragmented laterally. Close-up of the region indicated in g (h) with interpretive drawing (i) highlighting a single sublayer (dark grey in i) with tapering lateral tips; light grey shading in i denotes over- and underlying sublayers and dashed lines denote fractures.

Fig. 4: A polished vertical section through the fossil skin showing both upper and lower skin layers.

A fossil skin sample (sampling location shown in Fig. 2e) under natural light (a) and UV light (b); dashed lines indicate the approximate position of the polished section. c–g Scanning electron micrographs of the (uncoated) polished section showing the upper and lower fossil skin layers and the underlying sediment. Dashed lines in (e) denote the boundaries among the two fossil skin layers and the underlying sediment; note the isopachous cement surrounding sublayer fragments in (g). h Interpretive drawing of (e), showing fossil corneocytes (c) with fractures (f) and isopachous cement (i), and a dissolved pyrite framboid (p); stippled fill for the lower skin layer denotes melanosomes. See also Supplementary Figs. 6–8 for variations in melanosome distribution.

Fig. 5: A polished vertical sections through the fossil skin covered by sediment.

A fossil skin sample (sampling location shown in Fig. 2b) under natural light (a) and UV light (b); dashed lines indicate the approximate position of the polished section in (c). Note that in (b) the fossil skin (bright yellow) is mostly covered by sediment (purple). c–e Scanning electron micrographs of an (uncoated) polished section showing the fossil skin sandwiched between layers of sediment; dashed lines in (e) denote the boundaries among the upper and lower fossil skin layers and the underlying sediment. f Interpretive drawing of (e), showing fossil corneocytes (c) with fractures (f) and isopachous cement (i); stippled fill for the lower skin layer denotes melanosomes. g, h Close-up of the lower skin layer showing mouldic melanosomes. See also Supplementary Figs. 6–8 for variations in melanosome distribution.

Fig. 6: Elemental composition of the fossil skin.

Scanning electron micrograph (first panel) and EDS maps of a resin-embedded vertical section through the fossil skin (approximately the region shown in Fig. 4e). Dashed line in the scanning electron micrograph denotes the boundary between the fossil skin (upper layer) and the underlying sediment.

Yang, Z., Jiang, B., Xu, J. et al.
Cellular structure of dinosaur scales reveals retention of reptile-type skin during the evolutionary transition to feathers.
Nat Commun 15, 4063 (2024). https://doi.org/10.1038/s41467-024-48400-3

Copyright: © 2024The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

No serious palaeontologist sets out thinking, "How can I make creationists look like childish, scientifically illiterate fools?", they just look at the evidence and report it in peer-reviewed science journals. It's the evidence they discover and report that make creationists look like childish, scientifically illiterate fools; that, and the fact that they are, by and large, childish, scientifically illiterate fools, led by cynical frauds for money and far-right political aims, using religion for the excuses it traditionally provides.

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