Shedding/Molting of Scales or Feathers in Large Archosaurs?

[Phoebe Tausig]

Hi everyone,

Firstly, let me just say that getting to read all of the interesting discussions of this group is such a privilege. I am a high school student who has loved paleontology (specifically archosaur paleontology) since I was two years old and saw my first bones. Last August for my birthday I got to have an interaction with a live penguin, and observed them molting their feathers (which of course are modified scales). This got me thinking about shedding or molting of scales and feathers in other (extinct) archosaurs. Do we have any idea about it? Obviously scales or feathers in fossils are rare. I'm especially curious about pterosaurs also since they are the clade with no modern members. And, if modern dinosaurs appreciate being sprayed with mist in order to groom themselves, would extinct relatives appreciate the same or have a version of this behavior? 

Ps. Penguin feathers feel exactly like the scales of a lizard in case anyone wonders... 

[Thomas Richard Holtz]

Greetings,

As you guessed, there is little known. Our best information comes from small dinosaurs closely related to the origin of birds, because these have been found with their feathers in a few special lake deposits around the world.

Microraptor seems to show sequential moulting, allowing it to retain flight ability during the moulting phase: https://www.cell.com/current-biology/fulltext/S0960-9822(20)30862-9?uuid=uuid%3Ae08025b8-61d7-48c3-8e7d-16862ec4122b

But other feathered dinosaurs may have had different patterns: https://www.nature.com/articles/s42003-023-05048-x

I hope this helps,

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[Ronald Orenstein]

Hi Phoebe,

I am an ornithologist rather than a paleontologist, but allow me to offer a few comments.

Probably the reason for the evolution of moult in birds (and, presumably, other feathered archosaurs) is that feathers are subject to wear and attack by feather mites, but are not reparable.  They therefore need to be replaced, and in modern birds at least this happens on a regular basis either once or twice a year.  This sort of scheduling may have been necessary in order to retain the aerodynamic structure of the wing; indeed some birds become flightless during moult (obviously not an issue for penguins - which, by the way, are the only living birds to grow feathers from all parts of the skin and not just from feather tracts, presumably an adaptation to living in cold water).

This is quite different from the shedding process for living scaled reptiles such as lizards or snakes (or, for that matter, crocodilians), and subject to what I may learn from others on this list scale replacement comparable to moult in birds may not have been necessary for scaled dinosaurs (living birds, as far as I know, do not shed and regrow the scales on their legs and feet as part of the moulting process).

However, there is fossil evidence that at least one non-avian dinosaur, Microraptor, underwent a sequential moult cycle somewhat akin to that in birds:

https://www.cell.com/current-biology/fulltext/S0960-9822(20)30862-9?uuid=uuid%3Ae08025b8-61d7-48c3-8e7d-16862ec4122b

Here is a more recent paper pointing out that extensive searching failed to find evidence of moulting in other dinosaurs, and concluding that the yearly moult cycle we see today "may have evolved later, among crown birds":

https://www.nature.com/articles/s42003-023-05048-x

There is an entire book on the subject of moult in living birds, but it is very expensive!:  The Biology of Moult in Birds

The Biology of Moult in Birds The first comprehensive review of all aspects of the biology of moult, drawing information from across the liter...

Here is a paper on the evolution of moult in birds and mammals: https://royalsocietypublishing.org/doi/full/10.1098/rspb.2018.0318

I hope this helps!

Ronald Orenstein
1825 Shady Creek Court
Mississauga, ON L5L 3W2
Canada
ronorenstein.blogspot.com
ronorensteinwriter.blogspot.com

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[Gregory Paul]

Their caretaker urged me to pet a kiwi at the National Zoo in DC. Very smooth:)

There are a good number of molted feathers in Mesozoic and especially Cenozoic sediments. I don't know how shed pterosaur fibers would be identified even though they should be there. 

Did not know about the misting thing. Dinos prob would have liked it. 

Including Tyrannosaurus on a hot day;)

GSPaul

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[Mickey Mortimer]

There's also evidence of molting in Archaeopteryx- https://doi.org/10.1038/s42003-020-01467-2

And confuciusornithiforms- https://doi.org/10.1098/rsbl.2024.0106

And shed skin in Beipiaosaurus, Sinornithosaurus, Microraptor and Confuciusornis- https://www.nature.com/articles/s41467-018-04443-x

Mickey Mortimer

[Dawid Mazurek]

Is the scales to feathers scenario universally agreed on? My thinking was that, although there is a deep homology between these structures, primitive filaments arose sort of de novo, with no morphological intermediates between scales and filaments.

[Sean McKelvey]

Could the lack of morphological intermediates not just be the result of preservation bias? Correct me if I'm wrong here, but it's not like we have a sizeable pool of skin impressions from the right time/place?

On Sat, 8 Nov 2025 at 15:40, Dawid Mazurek <dawidma...@gmail.com> wrote:

Is the scales to feathers scenario universally agreed on? My thinking was that, although there is a deep homology between these structures, primitive filaments arose sort of de novo, with no morphological intermediates between scales and filaments.

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[Mickey Mortimer]

The lack of intermediates is hypothesized based on developmental studies, with Prum (1999) generally credited- https://prumlab.yale.edu/sites/default/files/prum_1999_mde_development.pdf . So basically the way feathers form, they would not have formed from scales, but would form instead of scales from the same structures in the embryo. Apparently recent studies continue to support this, though it's outside my area of expertise- https://doi.org/10.1007/978-3-030-27223-4_2 .

Mickey Mortimer

[Sean McKelvey]

Interesting, and duly noted. I have to admit that a lot of developmental biology is beyond me. Very interesting though.

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[Jura]

No, the de novo hypothesis is no longer supported. Work by Roger Sawyer and colleagues (e.g., Sawyer et al. 2003; Sawyer and Knapp 2003) found deep homology with scale development, up to and including the need to suppress (but not block) feather development for tarsal and foot scales to form.

Refs

Sawyer, R.H. and Knapp, L.W., 2003. Avian skin development and the evolutionary origin of feathers. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 298(1):57-72.

Sawyer, R.H., Salvatore, B.A., Potylicki, T.T.F., French, J.O., Glenn, T.C. and Knapp, L.W., 2003. Origin of feathers: Feather beta (β) keratins are expressed in discrete epidermal cell populations of embryonic scutate scales. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 295(1):12-24.

 

[Mickey Mortimer]

From my understanding, Prum also considered scales and feathers homologous at the level of the placode, just like Sawyer. Sawyer's saying Prum didn't get the developmental mechanism or ordering correct, but on a macro level I'm not sure Sawyer's proposing something different than 'instead of a scale forming, an elongated cylinder protofeather forms.' Sawyer and Knapp say "For example, outgrowths of the archosaurian skin would have created simple skin appendages in which certain epidermal cell populations were expressing scale- and/or feather-type b keratins", while Sawyer et al. say "We hypothesize that temporal and spatial changes in the expression of genes regulating development led to the formation of the first protofeathers in the archosaurian integument, which may have consisted of elongated barb ridge-like structures still enclosed in a tapering feather sheath."

Mickey Mortimer

[Jura]

Prum (2005) considered feather formation to be a novel structure largely unrelated to scales (though, to be fair Alan Brush was the first to call them this), which is in disagreement with Sawyer and others who argued for deep homology. This back and forth has met more towards the middle over the years, but the idea that feathers and scales had distinct origins persisted until relatively recently. This was mostly due to the lack of placode (localized epidermal condensations) formation in reptile scales (e.g., Prum and Dyck 2003; Musser et al. 2015). Bird scales do show a placode, which is partly what led to the common misinterpretation that bird scales are modified feathers. It wasn't until Di-Poï and Milinkovitch's (2016) work that we learned that all amniotes start their integumentary appendages from placodes. Reptilian placodes were hard to find because they formed at different times in different areas of the body. One couldn't just pick a developmental day and hope to find them. Reptile scales also form tracts at this stage, which also sounds a lot like bird feathers.

Refs

Di-Poï, N. and Milinkovitch, M.C., 2016. The anatomical placode in reptile scale morphogenesis indicates shared ancestry among skin appendages in amniotes. Science advances, 2(6):p.e1600708.

Prum, R.O., 2005. Evolution of the morphological innovations of feathers. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 304(6), pp.570-579.

Prum, R.O. and Dyck, J., 2003. A hierarchical model of plumage: morphology, development, and evolution. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 298(1):73-90.

Musser, J.M., Wagner, G.P. and Prum, R.O., 2015. Nuclear β‐catenin localization supports homology of feathers, avian scutate scales, and alligator scales in early development. Evolution & Development, 17(3):185-194.