New Study Refutes the Idea of Protofeathers in the Pterosauria

A newly published study casts doubt on the idea that members of the Pterosauria had an integumentary covering of insulating protofeathers.  Professor David Martill (University of Portsmouth), in collaboration with fellow flying reptile expert Dr David Unwin (University of Leicester), have reviewed the evidence and they propose that these vertebrates essentially lacked a feathery covering or indeed pycnofibres.

This research contradicts and refutes an earlier study published in the academic journal “Nature Ecology and Evolution” in 2018.

To read our article about the 2018 paper: Are the Feathers About to Fly in the Pterosauria?

Pterosaurs Uncovered – Lacking an Integumentary Covering

Picture credit: Megan Jacobs (University of Portsmouth)

Feather-like Branching Filaments

Dr Unwin and Professor Martill have challenged the findings of a research paper that examined the fossilised remains of two anurognathid pterosaurs which concluded that some of the structures preserved in association with the fossil bones were pycnofibres with characteristic features of feathers including non-vaned grouped filaments and bilaterally branched filaments.  The 2018 paper implied that if pterosaurs as well as dinosaurs had feather-like body coverings, then this type of integumentary covering was deeply rooted in the Archosauria.  This would suggest that the common ancestor of both the Pterosauria and the Dinosauria evolved this type of body covering.

If this interpretation of the fossil evidence is correct, then the very first feather-like elements evolved at least eighty million years earlier than currently thought.  It would also suggest that all dinosaurs started out with feathers, or protofeathers but some groups, such as the Sauropoda, subsequently lost them again, the complete opposite of currently accepted theory.

Unwin and Martill challenge the interpretation of the material that featured in the 2018 paper.  The propose that tiny, hair-like filaments reported by Yang et al (2018), are not protofeathers at all but tough fibres which form part of the internal structure of the pterosaur’s wing membrane, and that the “branching” effect may simply be the result of these fibres decaying and unravelling.

Dr Unwin from the University of Leicester’s Centre for Palaeobiology Research commented:

“The idea of feathered pterosaurs goes back to the nineteenth century but the fossil evidence was then and still is, very weak.  Exceptional claims require exceptional evidence – we have the former, not the latter.”

Feather-like Filaments in Pterosaur Fossils

Picture credit: Yang, Jiang, McNamara et al

Considering Theories Related to the Pterosauria

Highlighting the difficulties of interpretating filament-like structures, Professor Martill commented that either way, palaeontologists have to take care when considering theories related to the Pterosauria, they have no extant equivalents so the reliance of fossil material is perhaps greater when compared to the Dinosauria with their close relatives the birds still very much with us.

Professor Martill observed:

“If they really did have feathers, how did that make them look and did they exhibit the same fantastic variety of colours exhibited by birds.  And if they didn’t have feathers, then how did they keep warm at night, what limits did this have on their geographic range, did they stay away from colder northern climes as most reptiles do today.  And how did they thermoregulate?  The clues are so cryptic, that we are still a long way from working out just how these amazing animals worked”.

The scientific paper: “No protofeathers on pterosaurs” by David M. Unwin and David M. Martill published in Nature Ecology and Evolution.

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Famous Feather Fossil – Probably Represents a Feather from Archaeopteryx

The feathers are flying when it comes to an iconic fossil, arguably one of the most significant in any vertebrate palaeontology collection – a single, carbonised feather from the Solnhofen area of southern Germany.

Described in 1861, this isolated feather specimen is regarded as the first fossil feather known to science.  Having been scientifically studied just two years after the publication of Charles Darwin’s “Origin of Species”, the “Urfeder” – first feather in German, a modern-looking bird feather preserved in lagoonal sediments laid down around 150 million years ago, sent shock waves around the scientific community when it was first described.

The Iconic Feather Fossil – Is this from the “Urvogel” (Archaeopteryx lithographica)?

The Application of Laser-Stimulated Fluorescence

Ever since its discovery, scientists have debated what sort of creature this single feather came from.  In February 2019, Everything Dinosaur reported on research conducted by a team of international scientists that applied a sophisticated imaging method called Laser-Stimulated Fluorescence (LSF) to reveal previously unseen details in a forensic examination of both the slab and the counter slab of the fossil feather.  The team, which included Dr Michael Pittman (University of Hong Kong), proposed that the feather did not come from the famous “first bird”, but instead from an unknown species of dinosaur that co-existed with Archaeopteryx.

To read our blog post from February 2019, that disputed the claim that this specimen represented a feather from an Archaeopteryx: Iconic Feather Did Not Belong to Archaeopteryx.

New Study Re-affirms the Archaeopteryx Link

This new research utilised images generated from an electron microscope of the single feather specimen along with detailed examinations of known Archaeopteryx fossils that displayed feather impressions.  The study published in “Scientific Reports” was led by Ryan Carney, an assistant professor of integrative biology at the University of South Florida.  The researchers analysed nine characteristics of the feather, particularly the long quill, which runs up the centre of the specimen (centreline).  This centreline is composed of two parts:

• Calamus – centreline below the skin (shown in red in the diagram below)
• Rachis – tubular extension of the calamus above the skin (shown in blue in the diagram below)

The New Study Suggests The Single Feather Fossil is Congruent with Archaeopteryx Feathers

Picture credit: Carney et al (Scientific Reports)

The photograph (above), shows (a) centrelines of the isolated fossil feather modified from Hermann von Meyer’s original 1861 description and (b) Laser-stimulated fluorescence image modified from the 2019 scientific paper.  In (a) and (b), the centerline comprises the calamus (red) and rachis (blue).  An alignment error made in the earlier (2019) research led to the orientation of the centreline of the fossil feather to be out of the expected range found in extant birds (c).  The final figure (d) has been modified from (c) and shows a more representative range of centreline morphologies associated with modern birds (areas shaded yellow in (c) and (d).

A Feather from the Left Wing of Probably Archaeopteryx

Based on this new research, the scientists conclude that the single feather represents a feather from the left wing called a primary covert.  Primary coverts are small contour feathers that overlay the main wing feathers.  As similar feather characteristics were identified in other Archaeopteryx fossil feathers Carney et al conclude that the 1861 specimen probably does represent a feather lost by the famous “Urvogel” (Archaeopteryx lithographica).

Ryan Carney commented:

“There’s been debate for the past 159 years as to whether or not this feather belongs to the same species as the Archaeopteryx skeletons, as well as where on the body it came from and its original colour.  Through scientific detective work that combined new techniques with old fossils and literature, we were able to finally solve these centuries-old mysteries.”

The Location of the Fossil Finds

In addition, the research team looked at the provenance of the single feather, where it was found in relation to known discoveries of Archaeopteryx remains.  Four Archaeopteryx specimens, including the London specimen which is now the holotype for A. lithographica were found within 2.2 kilometres of the site where the single feather was discovered.  All of these specimens are coeval (having the same age and origin), from the same horizon in the limestone, all linked by biostratigraphy.  The Archaeopteryx material being associated with the same zonal ammonite fossils (Subplanites rueppellianus).

The Provenance of the Single Feather Fossil in Relation to Other Archaeopteryx Specimens

Picture credit: Carney et al (Scientific Reports)

Detecting and Interpreting Melanosomes on the Feather

The electron microscopy employed permitted the scientists to identify melanosomes (microscopic pigment structures).  They determined that this primary covert feather was coloured matte black.  Other studies have also shown the Archaeopteryx may have been black in colour, with some feathers showing iridescence.

The scientific paper: “Evidence corroborates identity of isolated fossil feather as a wing covert of Archaeopteryx” by Ryan M. Carney, Helmut Tischlinger and Matthew D. Shawkey published in Scientific Reports.

The Everything Dinosaur website: Everything Dinosaur.